59 Figure 3.8 CH4 conversion of NiO/SBA-15 catalysts with different contents of NiO .62 Figure 3.9 CO2 conversion of NiO/SBA-15 catalysts with different contents of NiO .63 Figure 3.10 C
INTRODUCTION AND LITERATURE REVIEW
Dry reforming Of methane - - - - - - << << <5 111 33333333331999933311 11111111111 1n ng v2 5
Dry reforming is the process to produce syngas based on natural gas and COz2 forH2/CO ratio equal to 1 The process not only helps to make use the COa-rich natural gas reservoirs above but also reduce effect of global warming Recently, CO: levels have increased by about 1.5 ppm per year, which means that if there were about 5.31021 grams of atmospheric air, about 8 billion tons of carbon dioxide per year [10].
CH¿ + CO; — 2CO + 2H; (AH208 = 246.2 kJ/mole) (1.1) Other reactions of process:
CH¿ + H20 — CO + 3H; (AHao¿ = 206 kJ/mole) (1.2) 2CHg4 + O2 — 2CO + 4H; (AHao¿ = 206 kJ/mole) (1.3)
The dry reforming of CHa process is usually accompanied by a Water Gas Shift (WGS) reaction and the formation of coke is generated through the decomposition of methane and Boudouard's reaction [11].
CO; + Hạ > CO + HạO (AHoos = 46.1 kJ/mole) (1.4) CHạ —› C + 2H; (AHzss = 74.9 kJ/mole) (1.5) 2CO — 2CO2 + Hạ (AHzứ = -172.5 kJ/mole) (1.6)
The thermodynamics of dry reforming (1.1) are not as favorable as autothermal reforming (ATR) or even steam reforming (STR) However, the consumption of one mole of carbon dioxide per mole of methane can reduce the effect of carbon, which results in "greener" natural gas consumption However, the thermodynamic barrier is an unfavorable challenge for processes with high reactivity Thus, using catalysts not only reduces the energy consumption but also increases the efficiency of the process [12].
The reforming of CHa process is a more potential heat recovery than the steam reforming process As a result, more energy is used than during steam reforming This leads to high energy costs and very expensive Another disadvantage of the dry reforming ofCH¿ process is the significant formation of coke on the surface of the catalyst resulting in deactivation in the reaction [11] This could be explained by the presence of COz in the feed consulting in high C/H ratio in the feed stream Moreover, as mentioned above,dry reforming of CHà process is a strongly endothermic process, so that, the catalyst is deactivated rapidly at high reaction temperature Thus, the stability of the catalyst is lower than those of other reforming processes of methane Research in dry reforming of methane has been concentrated on for recent years to improve conversion as well as limit the ability of coke formation.
Currently, catalysts used in dry reforming of methane based on precious metals were more active and had higher resistance to coke formation comparing with the ones based on Nickel metal Nevertheless, the high cost and low availability of noble metals limit their use as catalyst for reforming processes Thus, it was more effective to develop catalysts based on Nickel metal that were active resistant, to coke formation and stable for long term This could be done due to the fact that the support and the promoter have a great influence on the coke formation in process [13].
Catalyst for dry reforming of methane - + ++*2111155EEexesesesssss 7 IE5NW\ ¡(J0 1 4Ả
Catalyst development was one of the most important issues related to the reaction system The heterogeneous catalysts are easily separated after reaction finishes but the contact surface area is not high This is also the goal of the world's study of catalysts, to increase the surface area and coordinate the components to create the optimal catalyst for stability and activity.
More than 10 metals were studied and reported for reforming of CH4: Group VIII Ru (Ruthenium) [14], group [X Co (Cobalt), Rh (Rhodium), Ir (iridium) [15] and group X Ni (Nickel), Pd (Palladium), Pt (Platinum) [16] Among these metals, due to the low cost and availability of nickel metal, nickel should be used most in the reforming process However, catalytic performance, especially the catalytic stability of the catalysts based on nickel metal is not good enough Thus, current researches are focused on improving nickel-based catalysts by adding some metallic promoter such as Co, Ce, Researchers have proposed many ways to improve the Ni-metal catalyst system.
Iglesia et al [17] suggested that the rate of CH4 reaction depends only on the dispersion and presence of the Ni metal center, the formation of coke along with the increase in the diameter size of the Ni particles.
The most commonly used support for dry reforming of CHa was Al2O3, other supports such as MgO, TiOz, SiOz and La2O3 were also used [13] In 1994, Nakamura et al [18] carried out a study and he found that the effect of the metal support was in following order: Al2O3 > TiO2 > SiOz Studies have shown that the effect of the support could be attributed to direct activation of CH4 or COz by metal oxides and differences in particle size In 2008, according to Hyun-Seog Roh and Ki-Won Jun [19], both a- AlkO3 and y-Al2O3 supports were used Both Ni/a-Al2O3 and Ni/y-Al2O03 were unstable with time on feed stream for reforming of methane While Ni/a-Al2O3 has been reported to be unstable due to carbon formation, Ni/y-Al2O03 was unstable at high temperatures (973K) due to the phase change of the y-Al2O3 support.
Adding a small amount of alkaline metals such as Kali [20] or Natrium [21] to the catalyst could also alter the arrangement of Nickel metal on the support and promote gasification of coke, thereby reduce the effect of the coke on the activity of the catalyst.
Many studies have shown that catalysts with alkaline or alkaline-earth metals were added together to either achieve excellent COz conversion or anti-caking properties.
This could be explained by a change in the nature of the support when the promoter (alkaline/alkaline) was added Jun et.al [22] has reported that the Ni-Ce/ZrO2 catalysts were more active and stable than the Ni/ZrO2 or Ni/CeO:2 catalysts The addition of ZrO2z improves the oxygen storage capacity of CeO›, the thermal resistance and Nickel dispersion Moreover, the reducibility of CeO; is greatly enhanced when it is mixed with Zrệ to form Ce}-xZrxO2 [23].
I Luisetto et al [24] has reported cobalt-nickel alloy was formed in the Co-Ni/CeQOz bimetallic-catalyst Co-Ni/CeO2 catalysts were more active and have better selectivity than Co/CeOz and Ni/CeO2 monometallic catalysts in dry reforming of CH4 reaction Both catalysts containing cobalt, Co-Ni/CeO2 and Co/CeO;, showed significantly higher resistance to coke formation than Ni/CeO2, suggesting that Co is more effective in preventing the coke formation Yamazaki et al [25] developed a catalyst of Ni/MgO-CaO which had high basicity due to the presence of CaO Formation of coke was lower on this catalyst Presently, support mixtures are more concerned with improving catalytic performance, such as Ce1-x-ZrxO2, ZrxO2 [26], LaBOs [27] (B = Co,Ni, Fe, Cr) and LazNiOa In addition, Hayakawa et al [28] found that Ni/CagSi2TiO3 and Ni/BaTiO3 catalysts exhibited high activity and stability Suitable supports must withstand high temperatures and must maintain a metallic dispersion of the catalyst during the reaction Bhattacharyya and Chang [29] proposed to use nickel aluminate spinel catalysts to reduce coke formation during dry reforming Magnesium aluminate spinel (MgA12Oa) provides a desired combination of properties for use in ceramics, due to its high melting point (2135 °C), good chemical stability and mechanical strength.
Due to its low acidity and adhesion ability, such spinel has been widely studied as a catalyst for the catalytic steam reformation of methane Nowadays, MgAlzOa was being used as a support in “Oleflex” and “Star” processes for propane and butane depletion.
Recently, Tsyganok et al [30] reported a Ni-Mg-Al composite oxide catalyst derived from a double-layer hydroxide precursor When reduction with hydrogen, the catalyst has a high stability, stability and reusable catalytic function for dry reforming of CH4.
Moreover, Shishido et al [31] prepared Ni/Mg-Al catalysts from pre-hydrotalcite precursors exhibited higher activity than those prepared by conventional impregnation such as Ni/a-AlzO03 and Ni/MgO A commercial catalyst containing 12-14 wt.% of Ni on MgAI2O4 support was investigated by Gadalla and Bower [32] The conversion was only 86%, lower than the equilibrium conversion, obtained at steady state at 940 °C with CH¿/CO; ratio was 2.38 The report showed that MgAl,O4 was more stable thermodynamics than Al2O3 This work focuses on the development of a stable catalyst using MgAlzệ4 spinel prepared from the co-precipitation method.
Another improved substance was investigated to increase the surface area of the catalyst as CeO2 by Laosiripojana and S Assabumrungrat [33] Cerium oxide (CeO2z) or cerium is an important material for many catalytic reactions involving the oxidation of hydrocarbons (catalysts for the treatment of automobile emissions) Nowadays, a potential application of ceria was in solid oxide fuel cells in dry reforming of CH4 catalysts [34] with the ability to reduce the formation of large coke, ceria is a good candidate for dry reforming, especially the high surface ceria (Ce-HSA) The rate of dry reforming on CeQ2 (HSA) is proportional to the methane gas pressure and temperature of the system Carbon dioxide has a significant effect on the CH4 conversion, while carbon monoxide inhibits the reaction rate Hydrogen is found to have significant inhibitory effects on the metabolism of methane This inhibitory effect is the major disadvantage of using CeQO2 as a catalyst for dry reforming and removal of hydrogen during reforming as required.
In addition to these methods, the choice of solvent ethanol (C2HsOH) for water has also been investigated [35] Adjusting gas flow, gas composition during the reaction [36] and adding more modifier chemicals [37] in co-precipitation method all could affect to partial size of the catalyst.
Currently, supports are being studied for dry reforming incorporation including Santa Barbara Amorphous 15 (SBA-15), alumina (Al2O3), zirconia (ZrO2), titanium oxide (Ti02), magnesium oxide (MgO), and some other materials The general characteristics of these catalysts are their high specific surface area and high thermal stability In addition, recent studies tend to use two supports to mix together to improve catalytic efficiency [38] SBA-15 support was developed by Zhao [39], having large surface area of the SBA-15, well-defined pore structure, inert, non-toxic, highly biocompatible [40], thermal stability and hydrothermal [39], allowing SBA-15 to be used in catalysis, adsorption, and chemical sensors [41], pharmaceutical and chromatographic separation [42].
Othman et al [43] studied on the morphology and structure of SBA-15 SBA-15 shows the structure of the "hemp" at the ends and structure "chain" along the length.
Channels are interconnected by porous microstructure The large porosity of the material is responsible for increasing the contact area between the catalyst and the reactants as the active centers are dispersed evenly over the support surface In addition, the material structure of the SBA-15 can be flexibly modified for a specific purpose Because of the advantages mentioned above, the use of Ni catalysts supported on SBA-15 for reforming of CHa promises significant improvement in catalytic activity and stability Stediabudi and colleagues [44] studied the effects of Ni content on catalytic activity of Ni/SBA-15.
S5Ni/SBA-15 (5 wt.% Ni) showed superior performance with the highest stability compared to 3Ni/SBA-15 (3 wt.% Ni) and 10Ni/SBA-15 (10 wt.% Ni) CH4 and CO; conversion on this catalyst were 89% and 88% respectively while H2/CO ratio was 1.02.
Kinetics research for dry reforming of methane 5-5 ++<<+++++++++ssss 12
Kinetics research of dry reforming of CH4 has been studied for many years.
Reforming of CH4 was a complicated process It involved not only the mass transfer process, diffusion of reactants and products on the catalyst surface as well as from the outside in the catalyst but also included parallel or consecutive reactions To be able to widely apply this process in simulation and industry, design reactors and find the optimal conditions for the process, the mechanism and kinetics of the process was extremely important [50].
In 1996, Wang and his colleagues [51] proposed the mechanism included three main steps as follows: (1) decomposition of CHg to form C and H on the catalyst surface, (2) dissociation process of COz and H›, (3) reduction process of CO to form CO The reactions could be written as below:
On active metal surfaces, CH4 was adsorbed and dissociated to form H and CHx hydrocarbons, the value of x varied from 0 to 4 depending on the reaction conditions If the value of x equals to 0 means that the presence of carbon formation on the catalyst surface, the dissociated H will then combine to form Ha molecules and be adsorbed into the gas phase.
The reactions could be described with M indicated metal active sites and S indicated the support as below:
CHa + 2M > CH3-M + H-M (1.12) CH3-M + M > CHạ-M + H-M (1.13) CHo-M + M > CH-M + H-M (1.14)
The presence of alkali metals, alkaline earths, and other metals (P) could enhance the catalytic activity, provide oxygen simultaneously to prevent the formation of carbon on catalyst surface [52], the reaction process was given as below:
CO2 was activated on metal active sites to generate forms of carbonate, carbonates were then reduced by CHx compounds to form CO [52] The processes were described as below: e For acidity support:
CO2+ M 2 CO2-M (1.19) CO2-M + M 2 CO-M + O-M (1.20) CO-M 2 CO+M (1.21) e For basicity support:
CO; 2 CO2-S (1.22) CO2-S + OF 2 CO7 -S (1.23)
Many kinetic models were studied, the Power Law model (1.27) was used quite universally to calculate the kinetics for dry reforming The main advantage of this model is the simplicity of applying and estimating parameters as the reaction order However, it cannot fully explain the various steps in the reaction mechanism that occur on the catalyst surface [53].
Power Law model calculated kinetics for dry reforming of methane was given below: rk] Pou, | | Peo, | (1.27)
Where, k is constant of reaction rate represented by Arrhenius equation and m, n is different according to reactants (CH4 and CO2). k=k,er"" (1.28)
Kinetics for reforming of CH4 depends on the catalyst and the reaction mechanism can be changed according to different temperature ranging Kinetics was studied by Takano et al [54] obtained the reaction rate expressed approximately by the basic Power Law equation on Ni catalysts based on different supports In particular, the reaction rate of CH4 on Ni/Al2O3 catalysts was given below:
Where: e ko =4,5~x 10? (mol.Pa®*.s kg cat); e E@.1 (kl.mol); e R=8.314 (J.mol!.K'!).
In addition, Langmuir-Hinshelwood (LH) model also received much attention from researchers [55] due to the suitable mechanisms and experimental results For this model, both reactants were first absorbed on the surface before the reaction facilitated the interaction between the reactants, then the product was dissolved from the catalytic surface The reaction is best when the adsorption process of the reactant on the catalyst surface is balanced and evenly dispersed on the surface.
Langmuir-Hinshelwood Mechanism: Ỷ |surface surface | surface |
Figure 1.4 Langmuir — Hinshelwood mechanism The reaction periods are described by following equations:
B,,,+Z = BZ (1.32) AZ+BZ => CZ+Z (slow step) (1.33) CZZ,,,, +2 (1.34)
Where: Z is active site on catalyst surface
In Langmuir — Hinshelwood mechanism, the adsorption of A and B on catalyst surface is the reverse step, the reaction between A and B to form CZ + Z is the slow step If there is only one active site type on catalyst surface and assume that A and B is adsorbed on one active site type, reaction rate according to Langmuir — Hinshelwood was had a form as below:
Eley — Rideal proposed there was only one reacted gas (example gas A) A reacts with B from the gas phase on active site and generate C The mechanism is shown in figure 1.5:
Figure 1.5 Eley — Rideal mechanism The reaction periods are described by following equations:
A gas — Am (1.36)Avs + Bas ~— Cự, (slow step) (1.37)
In Eley - Rideal mechanism, the adsorption of A on catalyst surface is the reverse step, the reaction between A and B to form C is the slow step Kinetic equation according to Eley - Rideal mechanism had a form as below: way Ka Pa Ps
Gokon et al [56] examined the suitability of four different kinematic models:
Langmuir-Hinshelwood model, Power Law model, Eley - Rideal model, Stepwise (SW) model for dry reforming of methane on Ru/a-Al2O3 at temperatures range of 600 °C - 750 °C with CH4/CO>2 ratio changing from 0.3 to 3.0 at total pressure of 1 atm The total gas flow velocity is 5.0 L/min at temperature range of 600-700 °C and 2.5 L/min at temperature of 750 °C In conclusion, Langmuir-Hinshelwood model is the most suitable prediction for theoretical of dry reforming reaction rate with the assumption that both reactants (CH4 and CO2) are adsorbed into the catalyst at thermal equilibrium and generate to form H; and CO The reaction rate equation obtained from Langmuir- Hinshelwood model is:
KK 6, Koy,-Poo, P r= ae (1.40) (I+ Koo, Poo, + Kon, Poot,
Where: e Pou, , Poo, — partial pressure of CH4 and CO; â Koy, Koo, — equilibrium constant of CH4 and Cễằ; e k-—reaction rate constant for dry reforming of CH4. k, Koy, „Keo, is given by below: e k =1.17x10* exp(—83,498/RT), mol.L.s! e Kay, =0.653.exp(16.054/RT), atm’! © Koo, =3.11x103.exp(49,220/RT), atm!
In most cases, CH4 decomposition was considered to the decisive step (slow step) in steam reforming of CHa, but the deceleration step will change in the case of active supports in the reaction mechanism The activation energy (Ea) of the reaction was within wide limits, possibly due to different temperature, pressure, composition or catalysis conditions with different active phases, synthesized by different methods.
Kinetic assessment of the mechanism for dry reforming of CH4 on Ni/MgO catalyst was studied by Junmei Wei and Enrique Iglesia [17] Support based on Ni catalyst were CeO;, ZrOz and their oxide mixtures Oxygen storage and oxidation properties reduce the effect of coke, making them superior to conventional Alz03 or MgAI2O supports.
Reaction rates on Pd/CeO2 catalysts were higher than Ni catalysts Experimental results show that reforming of CHg is carried out according to the dual function mechanism, in which oxygen from Ce reacts with CH¿ dissociation on the surface of Pd metal.
However, the reaction strongly depends on the Ce metal and the high calcination temperature of the Ce can reduces ability of oxygen transfer [57].
Objectives and scopes Of research - c c1 1100111111199 1 1111111 1n ng 25
In previous studies, content of Nickel was commonly used ranging from 5 to 15 wt.% Due to the advantages of high surface area, high compatibility, low toxicity of SBA-15 support, study on Ni/SBA-15 catalysts for dry reforming of CH¿ with higher Nickel content to test the dispersibility, catalytic performance of SBA-15 to define the most suitable Nickel content for Ni/SBA-15 catalyst Simultaneously, kinetic research on the most suitable catalyst is carried out to define the influence of temperature, partial pressure of reactants and products to kinetics To attain the primary objectives, various following specific objectives were framed: e To prepare SBA-15 support by sol-gel method. e To prepare NiO/SBA-15 catalysts by impregnation method with 10 ~ 50 wt.% of NiO content. e To characterize synthesized catalysts using X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), Nitrogen Adsorption method (BET), Temperature Programmed Desorption (TPD), Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM). e To test the catalytic performance including CH4, CO2 conversions, Ha, CO selectivity, H2/CO ratio of Ni/SBA-15 catalysts. e To examine reaction rate according to temperature reaction, partial pressure of reactants and products for dry reforming of CHa on the most suitable Ni/SBA-15 catalyst among tested ones. e To propose the kinetic equation for dry reforming of CHa.
EXPERIMENTAL SECTION 7G G0 9590 0 8996 26
Catalyst preparation 01
- Nickel hexa-hydrate Ni(NO3)2.6H20 (Merck) M = 290.79 g/mole - Tetra ethyl orthosilicate TeOS (C2HsO)aSi (Merck) M = 208.33 g/mole - Pluronic P123 Poly(ethyleneglycol) — poly(propyleneglycol) — poly
(ethyleneglycol) (Basf) M = 5,750 g/mole - Hydrochloric acid fuming HCl 37% (Merck)
- Tool: scale 4 number, beaker (50, 100, 500 mL), biuret, pipet, glass chopstick, sieve tool (0.25 and 0.5 mm), grinding tool, taken sample syringe.
- Equipment: stirring machine, auto clave, drying equipment, heater, ultrasonic machine, squeezing ball equipment.
Table 2.1 Samples of catalyst prepared with different contents of NiO
Catalyst Support (wt.%) NiO (wt.%) Ni (wt.%) 10Ni0/SBA-15 90 10 7.86 20Ni0/SBA-15 80 20 15.72 30NiO/SBA-15 70 30 23.58 AONi0/SBA-15 60 40 31.44 50NiO/SBA-I5 50 50 39.30 2.1.4 Catalyst preparation procedure
Pluronic P123 was dissolved 4 grams with 105 grams of distillated water, the solution was stirred until be transparent in 30 minutes to get solution I After that,solution I was added slowly more 9.2 mL of TeOS and continued stirring in 30 minutes to get solution II 24.3 mL of HCI solution was then added to solution II to get solution
III, solution III was continued stirring in 30 minutes The final solution was aged in autoclave equipment at 60 °C for 24 hours After one day, this suspension was cleaned with distillated water under vacuum condition The precipitate was then dried at 80, 100, 120 °C in 2 hours per each temperature respectively before calcining at 550 °C for 10 hours to take the final SBA-15 support.
With distillated water Under vacuum condition
2.1.4.2 NiO/SBA-15 catalyst preparation procedure
An amount of Ni(NO3)2.6H2O0 chemicals was calculated based on NiO content and dissolved in distillated water This solution was impregnated with support SBA-15.
Subsequently, Nickel was impregnated on the support and the magnetic stir was used to disperse the solid equally After that, the suspension was continuously dried at 80, 100, 120 °C in 2 hours per temperature respectively before calcined at 800 °C for 1 hour The final raw catalyst was acquired and available to test in dry reforming reaction after was reduced with hydrogen stream.
Figure 2.2 Scheme for NiO/SBA-15 catalyst preparation procedure
2.2 Analytical methods 2.2.1 X-ray Diffraction (XRD)
X-ray diffraction is used in two main areas: identifying the characteristics of material crystals and determining the structure of materials Based on the theory of crystalline construction, the lattice is made up of atoms or ions distributed regularly in spaces according to a defined rule The distance between atoms (or ions) in the lattice is about a few roughly equal to the X-ray wavelength Thus, when the X-ray beam hits the crystal surface and goes deep into it, the lattice can play the role of a class from special diffraction.
Figure 2.3 Diffraction of X-ray by a crystal
In XRD method, the diffraction, in general, solely occurs when the path difference between x-rays is equal to a whole number n of wavelengths that is the major content of Bragg law is given in equation (2.1). nd = 2dsin() (2.1) Where: e nis the order of reflection; e iis the wavelength of the incident beam (4 = 0.15406 nm); e dis the repeat distance between the reflecting planes (nm); e 0 is Bragg angle of the reflection (°)
The crystallite size can be calculated by the Debye-Scherrer equation is given as below:
B,.cos0 (2.2) e Dp is crystalline diameter (A) e kK is Scherrer constant, 0.94 e is X-ray wave length (A) e Bais angular width of peak in term of A (20) (radian) e 0 is Bragg angle of the reflection (°) lntensity ———
Figure 2.4 The illustration of full-width at half the maximum intensity
The basic synthesis of an X — ray spectrometer is shown in figure 2.5 above The X — rays from tube T are projected toward sample C which can be changed the desired ỉ angle to the incident beam by rotating around an axis that goes through O The counter D measuring the intensity of diffracted beam is fix—positioned on crystal C at the corresponding angle 29 and rotated to scan the angles from higher than 0° to 180°.
Experimental: The XRD result according to powder method, is analyzed on the D2 PHARSER machine diffraction device - Brucker firm The sample is grinded into a soft powder, forming a flat surface with a thickness of about 100 A, and then to measure.
The average error of method is about 2 - 5%, in some suitable conditions error may be smaller up to + 0.5%.
In this research, the XRD pattern of catalyst samples is measured by using the D8 Advance Bruker powder diffractometer with a CuKa radiation source at Center for Innovative Materials and Architectures (INOMAR) — Vietnam National University Ho Chi Minh city.
2.2.2 Surface Area Measurement (BET)The BET nitrogen physisorption analysis is based on the Brunauer-Emmett—Teller(BET) theory which was developed by scientist Stephen Brunauer, engineer Paul Hugh
Emmett, and physicist Edward Teller and published the first time in the Journal of the American Chemical Society in 1938.
This theory aimed to explain the physical adsorption of inert gas molecules (nitrogen, argon, etc.) on the solid surface, as a result applied to the measurement of the specific surface area of materials This BET theory is considered as an extension of the Langmuir theory, which is only applicable for the monolayer molecular adsorption, to multilayer adsorption with the following assumptions:
All adsorbing sites are equivalent.
There is a multilayer physical absorption of gas molecules.
The adsorbing gas adsorbs into an immobile state.
There is no interaction between adsorbate molecules on adjacent sites on the same layer and between the layers as well.
First layer: the heat of adsorption.
Higher layers: the heat of liquefaction.
Uppermost layer is in equilibrium with vapor phase.
P: pressure of gas Po: saturated vapor pressure of the liquid at the operating temperature W: weight of gas adsorbed at a relative pressure Po
Wm= weight of absorbable constituting a monolayer of the surface coverageC= constant that is related to the energy of absorption in the first adsorbed layer and magnitude of the adsorbent/adsorbate integration.
According to experimental results, a BET plot derived from equation (2.3) can be drawn in the range of 0.05 < @ = p/p, < 0.35 and shown in figure (2.7) The values of the slope A and the intercept I are used to calculate the monolayer adsorbed gas quantity Um and the BET constant c.
Consequently, the total surface area Stota and the specific surface area Sper are given by:
Where: e N is Avogadro’s number; e sis the adsorption cross section of the adsorbing species; e V is the molar volume of the adsorbate gas; e ais the mass of the adsorbent.
Pore size is measured by Barrett — Joyner — Halenda (BJH) method as the following equations: cos0.R.T.In Po Đo T,=Tg tt (2.9)
Where: e rx is the Kelvin radius of the pore; e rp is the actual radius of the pore; e tis the thickness of the adsorbed layer; e o is the surface tension; e Vm is the molar volume of gas adsorbed in the pore; e Ris the real gas constant; e Tis the temperature of measurement process; e 0 is the contact angle between the solid and condensed phase.
Experimental: Samples were measured at Manar Center, Ho Chi Minh City National University with NOVA 2200e of Quantachrome - USA Machine operating parameters: 100 - 230 V, 50/60 Hz The sample size was 0.0278 g, the analysis time was 93.5 minutes Specific surface area is determined by adsorption of Nz at 77.35 K and Po
= 756 mmHg All samples were removed of gas at 150 °C for 1 hour before were carried out N2 adsorption experiments.
Figure 2.8 BET device of Quantachrome firm
Temperature Programmed Reduction (TPR) is a technique that widely used for the characterization of solid materials The materials are usually the metal oxides, mix metal oxides or the dispersed metal oxides on the supports TPR method yields the quantitative information of the reducibility of the oxide’s surface, the heterogeneity of the reducible surface, associated with determination of the redox temperature of the active sites.
In TPR method, a reducing gaseous mixture (10 vol.% of Hz diluted in pure N2 in this situation) flows over the sample while the sample is heated up on the predefined values This mixture is then measured the changes in thermal conductivity at the exit of the sample container with appropriate detectors (thermal conductivity detector).
Particularly, in this thesis, NiO is reduced by Ha displayed as the equation below:
Figure 2.9 H2-TPR example signal diagram
RESULTS AND DISCUSSIONS Q0 09 50 53
Catalyst physicochemical properties . <1 1111111 EEESSSSsssssssesse 53
Figure 3.1 The small angle XRD-spectra of SBA-15 support
Figure 3.1 showed the small XRD pattern with small angle 20 in the range of 0.5-10° of the SBA-15 support From the above graph, 3 characteristic peaks of SBA-15 support appeared at 20 = 0.9°, 1.6° and 1.83° corresponding to (100), (110) and (200) plans respectively [44] The appearance of the diffraction peaks also confirmed that theSBA-15 material had a mesoporous structure with a high order of hexagonal system[78].
Figure 3.2 XRD spectra of NiO/SBA-15 catalysts with different contents of NiO
The XRD patterns of the 30NiO/SBA15, 40NiO/SBA15, 50NiO/SBA15, samples were shown in figure 3.2 According to ICDD software database, diffraction peaks at 20
= 37.2°, 43.3°, 62.9°, 75.4°, and 79.6° corresponding to (101), (200), (220), (311), and (222) plans characterizing the Ni active sites with centered cubic structure on the surface of SBA-15 support [44] These peaks of all catalysts appeared very sharply with high intensity, indicating that the NiO was ina crystalline state When NiO content in catalyst increased, the intensity increased showing bigger NiO crystalline size This shows that NiO particles exist in the free state, weakly interacting with the carrier SBA-15.
3.1.2 Surface area and pore volume of the catalysts
Table 3.1 Structural properties of NiO/SBA-15 cataslysts
SBET NiO crystalline size | Pore size | Pore volume Catalyst
50NIO/SBA-I5 201.79 20.97 6.079 0.261 a Estimate from N2 adsorption at -196 °C b Estimate from XRD by using Debye-Scherrer equation (2.2)
Table 3.1 showed surface area (Sper), size of Ni crystalline, pore size and pore volume of the catalysts Sper of all three catalysts was much lower than SBA-15 (Sper
= 550-900 m?/g [79]), ranging from 180 to 230 m'/g Coverage of pore of SBA-15 support by NiO particle as seen in TEM result (figure 3.6), could be the reason for the difference of Sper between SBA-15 support and catalysts [80] The decrease of surface area leaded to the decrease of reactant’s adsorption on the catalyst, thus, catalytic performance decreased according to previous studies [81] However, large pore size and pore volume could increase catalytic performance thereby reducing the limitation of surface area Pore size of all three catalysts was ranging 5.2-6.1 nm allowed the diffusion of CHa and CO: in channel of support due to kinetic diameter of CHa and COz was 0.38 and 0.33 nm respectively [82] Sper increased from 221.60 m?/g to 232.60 m?/g when raising content of NiO and decreased from 232.60 m?/g to 201.79 m^/g when content of NiO decreased from 40 wt.% to 50 wt.% Similarly, NiO crystalline size and pore size increased with increasing of NiO content from 30 wt.% to 40 wt.%, then decreased when NiO content continue to increase to 50 wt.% In conclusion, 40NiO/SBA-15 was the catalyst with highest Sper (232.60 m”/g) and highest pore volume (0.273 m?/g) among tested catalysts. mm BET =®=Pore volume
0 ' r 0.1530NiO/SBA-15 40Ni10/SBA-15 S5ONiO/SBA-15
S-4800 10.0kV 8.0mm x60.0k SE(M) 900nm Iẹ S-4800 10.0kV 7.9mm x60.0k SE(M) 500nm a 30Ni0/SBA-15 b 40Ni0/SBA-15 c 50NiO/SBA-15
Figure 3.4 SEM images of NiO/SBA-15 catalyst: 30NiO/SBA-15 (a), 40NiO/SBA-15
Figure 3.4 shows the SEM images of of 30NiO/SBA-15, 40NiO/SBA-15, and 50Ni0/SBA-15 samples The SEM result showed the surface of NiO/SBA-15 catalysts with large black solid as SBA-15 support was covered by small white solid particle of the NiO.
Figure 3.4 (a) showed that on the surface of the 30NiO/SBA-15 catalyst, the NiO active sites were distributed fairly with small particle size, although some active sites were agglomerated In figure 3.4 (b), the surface of the 40NiO/SBA-15 catalyst was different from the 30NiO/SBA-15 catalyst The NiO particles of catalysts were also distributed evenly but the size of the NiO particle on the SBA-15 support was larger As be shown in figure 3.4 (c), there were more NiO particles observed in the 50NiO/SBA- 15 catalyst’s surface Thus, the surface area of the catalyst would be significantly reduced (table 3.1), some porous pores were overshadowed by large particles.
3.1.4 Transmission electron microscopy (TEM) images
40Ni_SBA_15_nung_2h[ TEM ] JEM-1400 100kV x100k 100% c SONiO/SBA-15
Figure 3.5 TEM images of NiO/SBA-15 catalyst: 30NiO/SBA-15 (a), 40Ni/SBA-15
The TEM images of the samples were shown in figure 3.5 The "chain" structure along the length and shape of the “hexagon" at the top of the catalytic particle were observed characterizing SBA-15 support This was consistent with the results of previous reports [83] Besides, there were two types of NiO particles observed namely small sized of some nm particles NiO inside the pore and NiO particle with large-sized particles (50-100 nm) outside the pore.
As be seen in figure 3.5, most of the active sites were small, some bigger active sites were found to show aggregation From the uniformity of the active phase size and the support, the catalyst could show high catalytic performance and stable stability.
3.1.5 Characterization of reduction properties by H2-TPR
Figure 3.6 TPR pattern of NiO/SBA-15 catalysts with different content of NiO
The H2-TPR profile of NiO/SBA-15 catalysts were shown in figure 3.6 As can be seen, catalyst had two reduction zones The first reduction zone appeared at temperature ranging 300 — 500 °C with higher intensity and larger area while the second one was observed in the temperature range of 500-750 °C Obviously, two reduction peaks were corresponded to the reduction step of NiO: NiO — Ni” + Ni° The reduction peak at lower temperature was ascribed to the reduction of Ni** of NiO clusters with small and medium-sized NiO particles [84] while the peak at higher temperature peak likely corresponded to the reduction of Ni** of NiO species or mixed metal oxide phase with small-sized NiO dispersed deeply in pores or large-sized NiO sintered [85] Thus, almost active sites of catalyst were distributed at small and medium-sized particle Based on previous studies, Ni” was reduced to Ni? without passing through the intermediate oxide phase, the reduction phase appeared at different temperatures for different catalysts [85].
From the results of the TEM and H2-TPR, it could be concluded that NiO particles outside the pores were dominated As NiO content was increased, the reduction peaks shifted toward higher temperature and higher consumption of Ha was observed This might be related to an increase in particle size as the NiO content increases (as observed from XRD and TEM results).
3.1.6 Result of adsorption and desorption of CO2 by TPD
Figure 3.7 TPD pattern of NiO/SBA-15 catalysts with different contents of NiO
CO2-TPD results in the figure 3.7 reflected that catalysts with different amount of NiO exhibited different strength of basicity It could be seen that there were two desorption peaks in CQO2-TPD pattern appearing at 60-250 °C and 450-600 °C,corresponding to weak and strong basic sites These peaks shifted to higher temperature with increasing of NiO content from 30 to 40 wt.% indicating a stronger CO2 affinity of40NIO/SBA-IŠ catalyst When NiO content was raised from 40 to 50 wt.%, desorption peaks was lower when increasing content of NiO from 10 to 40 wt.% On the other hand,when content of NiO was raised from 40 wt.% to 50 wt.%, the area of desorption peak was higher This fact showed the presence of basic sites with similar strength when there was a bigger amount of NiO.
Table 3.2 CHa conversion (%), CO2 conversion (%), CO selectivity (%), H2z selectivity and H2/CO ratio of NiO/SBA-15 catalyst with different content of NiO at temperature ranging 550 - 800 °C
TEC) | Xen (%) | Xe, 09 [CC 7 tal
3.2.1 Conversion of CH„ CO2 graph
Figure 3.8 CH4 conversion of NiO/SBA-15 catalysts with different contents of NiO
5 ¥ —A— 40NiO/SBA15 ° 60 -X-30NiO/SBA15 sp 4 ~% NiO/SBA15
Figure 3.9 CO; conversion of NiO/SBA-15 catalysts with different contents of NiO
The influence of temperature in dry reforming of methane was exhibited in table 3.2 on NiO/SBA-15 catalysts As be seen in figure 3.8 and 3.9, the conversion of both CHa and CO: increased following to reaction temperature ranging from 550 °C to 800 °C It was in an agreement of thermodynamic equilibrium of dry reforming of methane reaction Dry reforming of methane (AH29g = 246.2 kJ/mole) was strongly endothermic, thus, increasing of temperature lead to increasing of conversion It was noticeable that the conversion of CHy4 were very high in all catalysts and nearly reached to 95% at 800 °C,
As be seen in figure 3.8, 40NiO/SBA-15 catalyst showed the highest conversion of CHg at temperature ranging 550 — 800 °C This was consistent with surface area, pore volume result However, at high temperature the conversion of CHy4 was nearly the same on different catalysts At low temperature under 700 °C, the difference was more sharply, the catalyst with 10 wt.% of NiO showed the conversion of CH4 lower than other catalysts In addition, the figure 3.9 showed the same result of CO2z conversion via the change of temperature Besides, 1ONiO/SBA-15 catalyst had a large amount of basic sites but the strength of these sites was the same as other catalysts Increasing of temperature caused a dramatic rise of CO2 conversion in all catalysts but the difference
3.2.2 CO, H; selectivity and H2/CO ratio graph
= —A-40NiO/SBA15 6 70 4 -xX-30NiO/SBA15 © —x NiO/SBA15 c0 —>- 10NiO/SBA15
Figure 3.10 CO selectivity of NiO/SBA-15 catalysts with different contents of NiO
—X-20NiO/SBA15 sọ —©@- 10NiO/SBA15
Figure 3.11 Hz selectivity of NiO/SBA-15 catalysts with different contents of NiO
Figure 3.12 H2/CO ratio of NiO/SBA-15 catalysts with different contents of NiO
Figure 3.10 and 3.11 exhibited the selectivity (%) of CO and Hz respectively via changing of temperature In overall, CO and Hz selectivity were almost over 90% In addition, as be seen in figure 3.12, H2/CO ratio was nearly fit to 1 according to all NiO/SBA-15 catalysts in all temperatures which was consistent with ratio product in dry reforming reaction.
As it follows from above experimental results 40NiO/SBA-15 showed to be the best catalysts So, in next part of thesis the kinetics of reaction will be studied.
3.3 Kinetics research on 40NiO/SBA-1S catalyst for dry reforming of methane 3.3.1 The influence of internal and external diffusion to reaction
3.3.1.1 The influence of internal diffusion
The influence of internal diffusion was examined by comparing the reaction rate of dry reforming of methane on 40NiO/SBA-15 catalyst with different particle size: d 0.01-0.25; 0,25-0.50; 0.50-0.75; 0.75-1.0 mm The results showed that when changing the particle size from 0.01-0.25 to 0.50-0.75 mm, the reaction rate was unchanged as be seen in table 3.3 Thus, catalyst with particle size less than 0.75 mm had not affected by internal diffusion of reaction [86].
Table 3.3 The influence of particle size to reaction rate of dry reforming of methane
Size of particles | Conversion of CH4 | Conversion of CQO2 Reaction rate (mm) (%) (%) (mmol.g1.h-°) 0.10-0.25 90.0 72.8 331.48 0.25-0.50 91.1 73.4 335.53 0.50-0.75 87.9 71.4 323.74 0.75-1.00 74.3 56.8 273.65 3.3.1.2 The influence of external diffusion
The influence of external diffusion was examined by comparing the reaction rate of dry reforming of methane on 40NiO/SBA-15 catalyst with different total gas flows:
V = 6, 9, 12, 18, 30 and 36 L.h! The results showed that when increasing the total gas flow from 6 to 36 L.h!, the methane conversion decreased as be seen in table 3.4 This proves that there is no effect of external diffusion on reaction.
Table 3.4 The influence of total gas flow to reaction rate of dry reforming of methane
(T p0 °C, meat = 0.02 g, particle size: 0.25-0.5 mm, Poy, = Poo, = 30 hPa) Total gas flow | Conversion of CHa | Conversion of CO2 Reaction rate
Kinetics research on 40NiO/SBA-15 catalyst for dry reforming of methane
3.3.1.1 The influence of internal diffusion
The influence of internal diffusion was examined by comparing the reaction rate of dry reforming of methane on 40NiO/SBA-15 catalyst with different particle size: d 0.01-0.25; 0,25-0.50; 0.50-0.75; 0.75-1.0 mm The results showed that when changing the particle size from 0.01-0.25 to 0.50-0.75 mm, the reaction rate was unchanged as be seen in table 3.3 Thus, catalyst with particle size less than 0.75 mm had not affected by internal diffusion of reaction [86].
Table 3.3 The influence of particle size to reaction rate of dry reforming of methane
Size of particles | Conversion of CH4 | Conversion of CQO2 Reaction rate (mm) (%) (%) (mmol.g1.h-°) 0.10-0.25 90.0 72.8 331.48 0.25-0.50 91.1 73.4 335.53 0.50-0.75 87.9 71.4 323.74 0.75-1.00 74.3 56.8 273.65 3.3.1.2 The influence of external diffusion
The influence of external diffusion was examined by comparing the reaction rate of dry reforming of methane on 40NiO/SBA-15 catalyst with different total gas flows:
V = 6, 9, 12, 18, 30 and 36 L.h! The results showed that when increasing the total gas flow from 6 to 36 L.h!, the methane conversion decreased as be seen in table 3.4 This proves that there is no effect of external diffusion on reaction.
Table 3.4 The influence of total gas flow to reaction rate of dry reforming of methane
(T p0 °C, meat = 0.02 g, particle size: 0.25-0.5 mm, Poy, = Poo, = 30 hPa) Total gas flow | Conversion of CHa | Conversion of CO2 Reaction rate
In experiment, the catalyst was used with a particle size of 0.25-0.50 mm and a gas flow velocity of 6-36 L.h'! to assure that the reaction was carried out in the kinetic zone and calculated equation reflected the kinetic rule of the reaction The circulating flow method with a flow velocity of 100 L.h! circulation pump was much higher than that of the gas mixture to assure small conversion (< 15%) after each cycle of reaction and non- gradient of concentration, temperature The total reaction rate of each reaction at the output of the reactor is defined by equation (2.15).
3.3.2 The influence of temperature to reaction rate
The form of the kinetic equation for dry reforming of CHa was defined by examination of the dependence of the reaction rate according to the temperature in the Arrhenius coordinate system Experiments were carried out at different temperatures:
600, 650, 700 and 750 °C with a total flow velocity ranging from 6.0 to 36.0 L/h Results of experiments were presented in table 3.5.
Table 3.5 Reaction rate (r) for dry reforming of methane on 40NiO/SBA-15 catalyst at different temperatures ranging 600-750 °C
T V Pou, Poo, Puy Poo Fexp Fcal Error
No : Meat Xe, CC) | (L/h) hPa m.mol/g.h %
From data in table 3.5, the graph of the dependence of reaction rate according to conversion of CHg at different temperatures was showed Under above conditions, the conversion of CH, varied from 0.26-0.95 The dependence of reaction rate according to reaction temperature was shown in figure 3.13.
0 LI LI LI LI LJ LJ LI LÌ 20 30 40 50 60 70 80 90 100
Figure 3.13 The dependence of reaction rate (r) according to conversion of CH (Xem,
) at different temperatures on 40NiO/SBA-15 catalyst (Meat = 0.02 g, Poy, = Peo, = 30 hPa, Py, = Pco = 0 hPa)
Based on figure 3.13, the reaction rate’s plot at all temperatures was curved and the reaction rate was decreased when increasing conversion of CH4 This demonstrated that the product inhibited the reaction rate.
From the graph in figure 3.13, X¢y,= 0.5 was selected to define the reaction rate at 4 different temperatures (T = 600, 650, 700 and 750 °C) Results were presented in table 3.6 The isolation rule was assured by this method, in reaction there was only change of temperature, other factors were fixed.
Table 3.6 The dependence of reaction rate (r) on reaction temperature (T) on
(Pch, — Fco,= 30 hPa, Py, = Peo =0 hPa, Xcn, — 0.5)
Based on result in table 3.6, the dependence of reaction rate on temperatures was shown in figure 3.14
Figure 3.14 The dependence of logarithm of reaction rate (log(r)) on inverse temperature (1/T) on 40NiO/SBA-15 catalyst
(Meat = 0.02 2, Pen, = Peo, = 30 hPa, Py, = Pro — 0 hPa, Xcn, =0.5)
Reaction rate was a function of temperature expressed in logarithmic form in figure 3.14 The non-linear dependence of log(r) on 1/T in the Arrhenius coordinate system indicated the kinetics of equation was not an exponential equation but a fractional equation.
3.3.3 The influence of partial pressure of CH, to reaction rate
The influence of partial pressure of CH, to reaction rate in dry reforming of CH¿ on 40NiO/SBA-15 catalyst was investigated The results were presented in table 3.7 -3.8 and figure 3.15 - 3.16.
Table 3.7 The dependence of reaction rate (r) on partial pressure of CH4 (T = 700 °C, mea = 0.02 g, P&y,= 15-30 hPa, Bo, = 30 hPa, P?, = P& = 0 hPa) pe, | V Pou, | Peo, | Pu, | Peo | rexp | rea | Error
No ‘ Meat | Xcu, (hPa) (L/h) () hPa m.mol/g.h %
From the data in table 3.7, the graph of the dependence of reaction rate on conversion of CH¡ at different partial pressures of CHa (Péy, = 15; 20; 25 and 30 hPa) at temperature of 700 °C was shown in figure 3.15.
1200 - & P°cHs = 30 hPa ® P°cHa = 25 hPa 1000 ơ r đ P°cna = 20 hPa ê P°cHa= 15 hPa
0 LI LI LI LI LJ LJ LI LI 20 30 40 50 60 70 80 90 100
Figure 3.15 The dependence of reaction rate (r) on conversion of CH4 (Xem, ) at different partial pressures of CH4 on 40NiO/SBA-15 catalyst (T = 700 °C, meat = 0.02 g, Pey,= 15-30 hPa, Pg, = 30 hPa, Py, = Pg = 0 hPa)
From the graph shown in figure 3.15, X¢;,=0.5 was selected to obtain 4 reaction rates at 4 different reaction modes with different partial pressure of CH4 The results were presented in table 3.8.
Table 3.8 The dependence of reaction rate (r) on partial pressure of CH¿ on
AQNiO/SBA-15 catalyst (P3;,= 15-30 hPa, P&,= 30 hPa, P§, = P% =0 hPa, Xcy, = 0.5)
From the data in table 3.8, the dependence of reaction rate on the partial pressure of CH4 at the conversion Xu, = 0.5 was shown in figure 3.16.
Figure 3.16 The dependence of reaction rate (r) on partial pressure of CH4 on
From the graph shown in figure 3.16, the curve showed the dependence of reaction rate on the partial pressure of CH4 on 40NiO/SBA-15 catalyst had form of concave curve with high slope The reaction rate was strongly influenced by the partial pressure of CHa, when the partial pressure of CHa increased, the reaction rate increased rapidly consistent with the previous studies [81, 87] This could be predicted that CH4 appeared in both numerator and denominator.
Since the activation process of CH4 produced intermediate groups H and C, an amount of H activated CO2 to generate CO and OH groups adsorbed on the catalyst surface, carbon particles were removed through reaction with the hydroxyl group (C-S + OH-S CO-S + H-S), this step was considered be the slow step of this reaction.
When increasing the partial pressure of CHa, the reaction rate increased and H; was generated more However, when the CHa partial pressure was high, due to the existence increased within reaction to slow down the activation of CH, and the activation of CO2 [87] In addition, increasing the concentration of methane facilitated the formation of coke (1.5) takes place [11], led to deactivation of catalyst.
3.3.4 The influence of partial pressure of CO2 to reaction rate
The influence of CO2 partial pressure according to reaction rate for dry reforming of CH4 on 40NiO/SBA-15 catalyst was investigated The results were presented in table 3.9 - 3.10 and figure 3.17 - 3.18.
Table 3.9 The dependence of reaction rate (r) on partial pressure of CO2 (T = 700 °C, mea = 0.02 g, Bộ; = 30 hPa, P&,= 15-30 hPa, P?, = P& = 0 hPa)
P° V Pou, | Peo, | Pu, | Peo | rexp ra | Error
No ° Meat Xe, (hPa) (L/h) () hPa m.mol/g.h %
From the data in table 3.9, the graph of the dependence of reaction rate on conversion of CH, at different partial pressures of CO; (Pco, = 15; 20; 25 and 30 hPa) at temperature of 700 °C was shown in figure 3.17.
Figure 3.17 The dependence of reaction rate (r) on conversion of CH4 (Xe, ) at different partial pressures of COz2 on 40NiO/SBA-15 catalyst (T= 700 °C, mea = 0.02 g, P&,= 30 hPa, P&,= 15-30 hPa, P?, = P&> = 0 hPa)
From the graph shown in figure 3.17, Xen,= 0.5 was selected to obtain 4 reaction rates at 4 different reaction modes with different partial pressure of CO2 The results
Table 3.10 The dependence of reaction rate (r) on partial pressure of CO; on
(T = 700 °C, PCh,= 30 hPa, Pco,= 15-30 hPa, Ps, = Peo = 0 hPa, Xu, = 0.5) Pổo, (hPa) 0 15 20 25 30
From the data in table 3.10, the dependence of reaction rate on the partial pressure of CO; at the conversion Xô,= 0.5 was shown in figure 3.18.
Figure 3.18 The dependence of reaction rate (r) on partial pressure of CO2 on
(T = 700 °C, meat = 0.02 g, Poy, = 30 hPa, Peo, = 15-30 hPa, Py, = Peo = 0 hPa,
From the graph shown in figure 3.18, the curve showed the dependence of reaction rate on the partial pressure of CO2 on 40NiO/SBA-15 catalyst had form of convex curve.
Figure 3.18 also showed that the reaction rate tended to increase when increasing the partial pressure of COz This could be predicted that COz appeared in both numerator and denominator of kinetic equation.
3.3.5 The influence of partial pressure of CO to reaction rate
The influence of partial pressure of CO according to reaction rate in dry reforming of CH4 on 40NiO/SBA-15 catalyst was investigated The results were presented in table 3.11 - 3.12 and figure 3.19 - 3.20.
Table 3.11 The dependence of reaction rate (r) on partial pressure of CO pe | vy Pou, | Poo, | Pa, | Peo | rap | reat | Error
No Meat Xen, (hPa) (L/h) () hPa m.mol/g.h %