Tổng hợp xúc tác cu fe SAPO 34 cho phản ứng khử xúc tác chọn lọc (SCR) NOx với NH3 TT TIENG ANH

MINISTRY OF EDUCATION AND TRANING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY DOAN ANH TUAN Synthesis of Cu-Fe/SAPO-34 catalysts for the selective catalytic reduction (SCR) of NOx with NH3 Major: Chemical Engineering Code No.: 9520301 THE ABSTRACT OF CHEMICAL ENGINEERING DOCTORAL DISSERTATION Hanoi – 2022 The dissertation was accomplished in Hanoi University of Science and Technology and Leibniz-Institut für Katalyse e V Adviors: Assoc Prof Pham Thanh Huyen Prof Le Minh Thang Reviewer No.1: Reviewer No 2: Reviewer No 3: The dissertation was defended before the scientific committee at HaNoi University of Science and Technology On the…………………………………… The dissertation information can be found at following libraries: Ta Quang Buu Library - Hanoi University of Science and Technology Vietnam National Library INTRODUCTION Motivation Nitrogen oxides exist in the environment in various species such as N2O, NO, NO2, N2O3, N2O4, and N2O5 By definition, the abbreviation NOx is used for nitric oxide (NO) and nitrogen dioxide (NO2) They are considered to be toxic and chemical precursors that lead to ground-level ozone, a ubiquitous air pollutant in urban areas A major source of NOx is generated during the combustion of fossil fuels from stationary sources such as coal-fired power plants and mobile sources such as diesel-powered vehicles Over the past years, many technologies including fuel control, combustion control and post-combustion control have been developed, and are commercially available for the control of NOx emissions Among these technologies, the selective catalytic reduction of nitrogen oxides by ammonia (NH3-SCR) is one of the most popular post-combustion techniques for NOx emission control and is worldwide applied in stationary sources and diesel vehicles due to its high efficiency, high selectivity and low cost Since the early 1970s, various catalytic materials have been developed for the SCR of NOx to meet the stringent regulation of NOx reduction The most popular NH3-SCR catalysts used for cleaning flue gases from power plants are V2O5-WO3/TiO2 oxides which, however, operate only in a slightly high and narrow temperature range of 300 - 500 °C Also, the toxicity of vanadium species is an issue Additionally, MnOx has been attracted significant interest in the development of low-temperature SCR catalysts With MnOx-based catalysts, almost total NOx conversion has been obtained already at temperatures well below 150 °C Although significant efforts have been given to the investigation of MnOx for low-temperature NH3-SCR, poor resistance to SO2 and H2O as well as large N2O formation are serious problems for practical applications In recent years, the ion-exchanged zeolites have been reported as promising catalysts for diesel vehicles due to their high adaptability to high space velocity Furthermore, zeolites have the advantage of inexpensive cost, nontoxicity and good thermal stability Recently, zeolites with even smaller pore window size with the chabazite structure attracted much attention in NH3-SCR for NOx elimination due to their excellent low-temperature activity and high hydrothermal stability Moreover, small pores have been considered decreasing the net dealumination rate, which will lead to enhancing the life span of the catalysts In any case, the presence of a transition metal ion is necessary since this ion acts directly as a redox catalytic center Many metals such as Cu, Fe, Ce, Co, Mn, etc have already been investigated for NH3-SCR of NOx Among them, Cu and Fe have been attracted significant interest due to their availability and high activity and suitable catalysts for the wide operating temperature window Fe-zeolites have shown better activity at high temperature (above 400 °C), whereas Cu-zeolites have been reported to reach higher activity at low to medium temperature (200 - 400 °C) The temperature of NOx-containing exhaust gases from other sources such as diesel or lean-burn gasoline engines is much lower around 150 - 300 °C, while the presence of moisture at the temperature of the soot and ash filter regeneration of a diesel particulate filters (DPF) often over 450 °C Moreover, the restricted volume of catalytic converters in these engines requires catalysts that are active under high gas hourly space velocity conditions but at low-pressure drop In this NH3-SCR technology, the catalyst should either work in a wide operational temperature range to be suitable for both light and heavy diesel engine exhaust or reduce NOx selectively to N2, and also, it would also need to withstand the SO2 and H2O from any hydrocarbon combustion effluents Therefore, the idea of NH3-SCR catalysts that the bimetal (Cu-Fe-) ion-exchanged zeolites can be used as an alternative material to obtain SCR catalysts with a high wide-temperature activity Metals loading on the catalysts mainly attributes to the catalytic performance while the carrier takes main responsible for the stability and selectivity production Among those small pore zeolite, SAPO34 with a chabazite topology was reported to show greater hydrothermal stability, then SSZ-13 or ZSM-5 The hydrothermal stability was needed when the temperature of the exhaust reaches above 650 °C with the moisturized environment during the regeneration of DPF section, which is generally placed in front of the SCR section SAPO-34 molecular sieves with low silicon content and uniform distribution are important for maximizing the selectivity of nitrogen SAPO-34 is synthesized by hydrothermal method in the presence of organic structure-directing agents (OSDAs) Various factors affect the properties of synthesized SAPO-34 including the chosen templates, the Al and Si sources, the molar ratios of Si/Al/OSDAs of the gel, the gel aging time and temperature, and the reaction time and temperature Among them, OSDAs and silicon sources play an important role in the crystallite size, the Si distribution as well as the framework charge density Despite a lot of investigations, the location of metal ions in zeolites, the nature, and the role of active sites, particularly the valence states of metal ion species under reaction conditions are controversially discussed Moreover, in the case of bimetal ionexchanged zeolites, the presence of bimetal ions and the interaction between them may exhibit influences on the catalytic performance of zeolite catalysts, since this interaction affects both dispersion and redox behavior of the active phase and also work function properties the use of bimetal ion-exchanged zeolites as catalysts for widetemperature windows of NH3-SCR of NOx is limited and the available information on the structure and the redox behavior of active sites in bimetal ion-exchanged zeolite catalysts is still very contradicting Spectroscopic in-situ studies as well as catalytic tests shall be performed with a series of systematically bimetal ionexchanged zeolite catalysts in the SCR of NOx with NH3, since the few known results promise a high potential in this important application field when the catalysts are optimized in a suitable way The scope of the research is to: The main objective of the thesis is “Synthesis of Cu-Fe/SAPO-34 catalysts for the selective catalytic reduction (SCR) of NOx with NH3” To make this approach efficient operando studies, exhaustive catalysts characterization and mechanistic studies will be also considered The new contributions of the dessertation The effects of different mixtures of organic structure-directing agents on the formation of SAPO-34 structure have been investigated Different templates, namely, triethylamine, tetraethylammonium hydroxide, and morpholine, and their combinations were used to synthesize SAPO-34 by a hydrothermal method The template concentration was optimized by eliminating the competing phases to obtain the purest form of the SAPO-34 phase Applying combined organic structure-directing agents including triethylamine, tetraethylammonium hydroxide, and morpholine has demonstrated to be an effective and cost-down method to synthesize SAPO-34 catalysts Also, the SAPO-34 molecular sieve has been synthesized under hydrothermal conditions by using a combination of tri-templates with different silica sources, such as TEOS and colloidal silica LUDOX AS-30 The extent and effects of silicon substitution on these materials have been investigated Using TEOS as silica source may result in uniform particles with a relatively small size and high surface area, as well as less amorphous silica amount So, the obtained results contributed to knowledge about the influence of organic structure-directing agents as well as silicon substitution on the formation of SAPO-34 material The SAPO-34 based and ZSM-5 commercial based with Cu-, Fe-, and Cu-Fe- were prepared through the ion-exchanged method in an aqueous solution The investigated catalysts have been applied in the selective catalytic reduction of NOx with NH3 at the normal reaction condition and the presence of SO2 and H2O conditions The results suggest that suitable metal content could promote NOx conversion, while the excessive Cu or Fe loading could block the “channel” of zeolites The synergistic effect between iron and copper in the CuFe/based catalyst prompted higher catalytic performance in more extensive temperature as well as hydrothermal stability and poisoning stability after iron incorporation Meanwhile, SAPO-34 based catalysts showed higher catalytic performance in more extensive temperature compared with ZSM-5 commercial based catalysts The Cu-Fe/SAPO-34 showed superior H2O and SO2 resistance, compared to Cu/SAPO-34, maybe because Fe supported onto the surface of catalysts, resulted the reaction with SO2 and H2O became much more efficiently, and then the Cu active sites were protected These results showed their potential application in industrial catalysts Spectroscopic in-situ studies are performed with a series of systematically ion-exchanged SAPO-34 catalysts in the selective catalytic reduction of NOx with NH3 since the few known results promise a high potential in this important application field when the catalysts are optimized in a suitable way The location of Cu and Fe ion in SAPO-34, the nature and role of active sites, particularly the valence states of Cu ion species under reaction conditions are controversially discussed The well-obtained values in the in-situ analysis would recommend the potential application of these bimetallic Cu-Fe/SAPO-34 for NOx removal in the operation of the wide-temperature window Structure of the dessertation The thesis book has 135 pages including Introduction (5 pages); Chapter State of the art (30 pages); Chapter Experimental (16 pages); Chapter Results and discussion (62 pages); Conclusions (2 pages); Publications of the thesis (3 pages); References (17 pages) CONTENTS CHAPTER STATE OF THE ART The main sources of environmental pollution are the exhausts from the transportation sector, including CO2, HCs, particulate matter, and NOx The emission of NOx from diesel engines can be reduced by catalytic treatment of the exhaust gases by the NH3-SCR In order of achieving high NOx conversions and high selectivity towards nitrogen and water, the selected catalyst and operating conditions should be a perfect match for the required reactions One of the most important aspects required for a commercially viable catalyst is hydrothermal stability Due to the placement of the SCRsection after the diesel particulate filter, the catalyst needs to withstand temperatures over 650 °C during the soot oxidation processes This type of intelligent catalyst selection and design, based on structure-activity relations, is of course only possible if the reaction mechanism involved is known Promising catalysts for the conversion of nitrogen oxides are bimetal-exchanged zeolites, whose characterization will be the main topic of this dessertation The discussion above clearly illustrates why Cu/SAPO-34 with its CHA framework has gained so much attention in the last few years This catalyst excels in terms of performance, due to the smaller pores, which increase the hydrothermal stability Furthermore, the main Cu-species present are isolated monomers, implying a great combination of activity and selectivity In addition, Fe/SAPO-34 has shown better activity at high temperatures, which could be a promising co-active site for increasing the temperature operation range in Cu/SAPO-34 catalysts Herein, the dissertation aimed to investigate the application of copper-iron bimetal ion-exchanged SAPO-34 for deNOx with NH3 reductant and compare with ZSM-5 commercial based CHAPTER EXPERIMENTAL 2.1 Preparation catalysts SAPO-34 molecular sieves were synthesized from a reaction mixture with molar composition of Al2O3 : 0.6 SiO2 : P2O5 : X OSDA(s) : 110 H2O for influence of OSDAs on the formation of SAPO-34 structure (X: TEA, TEAOH, Morpholine), while Al2O3 : Y SiO2 : P2O5 : Xb OSDA(s) : 110 H2O for influence of silicon sources for SAPO-34 formation (Y: TEOS or LUDOX AS-30) The M/SAPO-34 and M/ZSM-5 catalysts (where M = Cu-, Feor Cu-Fe-) were prepared by liquid ion-exchanged method with several contents 2.2 NH3-SCR activity test of catalysts In this study, the SCR reaction was carried out using a feed of 0.1 vol.% NH3, 0.1 vol.% NO, vol.% O2, balance He or the feed contained 1000 ppm NO, 1000 ppm NH3, vol.% O2, balance He The total flow rate of the feed was set at 100 mL/min, corresponding to a GHSV of 70000 h-1 The reaction was carried out in the temperature range of 100 – 600 °C (50 °C/step) Evaluation of SO2 poisoning exposition of 100 ppm SO2 under standard SCR conditions, while evaluation of H2O presence of 8.2% under standard SCR conditions 2.3 Research methods Catalyst characterization techniques include X-ray diffraction (XRD), inductively coupled plasma - optical emission spectrometry (ICP-OES), flame atomic absorption spectrometry (FAAS), field emission scanning electron microscopy and energy dispersive X-ray spectroscopy (FE-SEM and EDS), Brunauer – Emmett – Teller surface area analysis, fourier transformed infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance spectroscopy (29Si NMR MAS), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), Xray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) CHAPTER RESULTS AND DISCUSSION 3.1 The influence of OSDAs on the formation of SAPO-34 structure In the preparation of the SAPO-34 material, the crystallization process depends importantly on the type of OSDAs because of their interaction with inorganic species and the alkalinity, which have influence on both the nucleation and crystal growth rates The XRD patterns of all the prepared samples match well with SAPO-34 structures, except for sample S01 However, the reflection intensity and the width of peaks were different and depended on the templates Figure 3.1 XRD diffraction pattern of assynthesized samples Table 3.1 Physicochemical properties and crystallinity of the all samples Sample name S01 S02 S03 S04 S05 S06 S07 S08 Mean crystallite size (nm) 131.66 36.12 43.65 56.52 52.78 81.59 34.29 Crystallinity (%) 92.16 73.14 63.14 81.82 68.92 82.45 86.48 Average particle size (µm) 16 38 5 10 BET surface (m2/g) 210 480 707 725 683 466 440 797 FE-SEM images clearly show different morphology and crystal sizes of these samples Using Mor or TEAOH could observe SAPO34 which had cubic-like rhombohedra morphology with different crystal size Mixing different OSDAs leads to the formation of a pure SAPO-34 structure as well as reducing in particle size and proper arrangement in size distribution Figure 3.3 FT-IR spectra of S03 to S08 samples with a full range of wavelength Figure 3.2 FE-SEM images of assynthesized samples Figure 3.3 shows the IR spectra of SAPO-34 with differing the OSDAs type The broad stretching vibrational band between 3300 cm-1 to 3700 cm-1 is assigned to the bridging hydroxyl groups, which is evidence improving the generation of the Brønsted acidity of SAPO-34 According to the International Union of Pure and Applied Chemistry (IUPAC) classification, all of the product samples displayed the characteristic type I isotherm Figure 3.4 N2 adsorption and desorption isotherms of S03, S04, S05, S08 samples Figure 3.5 NH3-TPD profiles of S03, S04, S05, S08 samples The combination of tri-templates benefits for the Si incorporation into the SAPO-34 framework, leading to an increase in strong acid 11 Therefore, SAPO-34 synthesized with TEOS as silicon source is suitable for NOx removal by NH3-SCR 3.3 Copper-iron bimetal ion-exchanged SAPO-34 for NH3-SCR of NOx 3.3.1 Structure and texture of catalysts The final metal loading in all samples determined by ICP-OES analysis is close to the theory metal content calculated for catalyst preparation The typical structure of SAPO-34 was maintained during the aqueous ionexchange process This influence could consolidate the deposited copper and/or iron species on SAPO-34 could adsorb of the XRD or due to the treatment with neutral aqueous solutions, resulting to Figure 3.11 XRD patterns of asdecreased crystallinity synthesized SAPO-34 and catalysts Table 3.4 Physico-chemical properties and crystallinity of as-synthesized samples Catalyst Metal BET Avg Mean Crystallinity atomic Surface pore crystallite (%) (m2/g) dia size (nm) (wt.%) (nm) SAPO-34 797 0.75 34.29 86.48 1Cu/SAPO-34 1.06 583 0.69 34.77 75.06 3Cu/SAPO-34 3.02 501 0.60 35.64 72.29 5Cu/SAPO-34 5.02 357 0.47 36.76 67.68 1Fe/SAPO-34 1.01 555 0.65 34.60 74.04 3Fe/SAPO-34 3.02 487 0.60 38.30 70.94 5Fe/SAPO-34 4.82 332 0.44 39.43 62.67 1Cu1.36 Cu – 398 0.47 38.22 67.85 3Fe/SAPO-34 3.08 Fe 2Cu1.95 Cu – 479 0.53 36.49 70.82 2Fe/SAPO-34 1.93 Fe 3Cu3.01 Cu – 499 0.56 34.71 74.87 1Fe/SAPO-34 0.94 Fe 12 The addition of Cu and/or Fe did not change the CHA structure and crystal morphology of SAPO-34 Combined with ICP-OES and XRD results, this can be attributed that some large metal-containing agglomerations are welldistributed crystal metal oxides particles in the SAPO-34 structure Figure 3.12 FE-SEM images of all catalysts 3.3.2 Redox and acid properties results The catalyst co-doping with a mixture of Cu-Fe caused the formation of three desorption peaks which are broader and higher intensity than those of Cu/SAPO-34 This indicates the considerable number of acid sites of Cu–Fe/SAPO-34 catalysts, resulting in the formation of extra-framework Cu2+ from a part of bulk CuO An increase in the exchange capacity of Cu, therefore, can enhance the Lewis acid strength of Cu–Fe/SAPO-34, leading to a higher amount of adsorbed NH3 molecules on the catalyst Figure 3.13 Temperature-programmed desorption of NH3 catalysts Figure 3.14 H2-TPR profiles of catalysts The co-doping of Cu and Fe into SAPO-34 leads to shifting to the higher temperature of the first reduction peak compared to Cu/SAPO-34 This is due to the intense interaction between copper 13 and iron metallic components and integration in Cu-Fe/SAPO-34, making them more difficult to reduce 3.3.3 Cu and Fe species onto SAPO-34 For the Cu-Fe/SAPO-34 sample, the obtained result reveals that the bimetallic catalyst contained several active sites of both copper and iron Figure 3.15 UV–Vis DRS spectra of the catalysts Table 3.5 XPS quantitative analysis of the catalysts Catalyst Cu species (%) Fe species (%) Cu2+ CuO Fe2+ Fe3+ 3Cu/SAPO-34 39.65 60.35 1Fe/SAPO-34 69.62 30.38 3Cu51.15 48.85 62.24 37.76 1Fe/SAPO-34 Figure 3.16 XPS results of O 1s Figure 3.17 XPS results of Fe 2p O1s chemisorbed oxygen (%) 36.61 15.45 45.61 Figure 3.18 XPS results of Cu 2p Compared with a single metal/SAPO-34, the surface oxygen ratio of 3Cu-1Fe/SAPO-34 reached up to 45.61%, which demonstrates that Fe addition enhanced the surface oxygen vacancies of catalysts 14 The amount of Fe3+ on 3Cu-1Fe/SAPO-34 is higher compared to that on 1Fe/SAPO-34 Meanwhile, the amount of Fe2+ is lower due to the interaction between iron and the surrounding atom of copper, leading to an increase in the oxygen vacancies and charge transfer from the copper to iron 3Cu-1Fe/SAPO-34 catalyst has higher portion (51.15%) of Cu2+ than 3Cu/SAPO-34 without Fe These results have been identified with our previous research that the combination of iron solution and the Brønsted acid protons in 3Cu/SAPO-34 during preparation make the catalyst in an acidic aqueous environment, enabling the transformation of part of bulk CuO to the extraframework Cu2+ Compared to the sample 3Cu/SAPO-34, the intensity of axial Cu2+ signal in sample 3Cu1Fe/SAPO-34 is higher, indicating that the introduction of an appropriate amount of Fe led to increase the number of isolated Cu2+ ions Figure 3.19 EPR spectra of catalysts measured at room temperature 3.3.4 Catalyst performance Figure 3.20 a) Comparison conversion of NOx during the standard NH3-SCR and b) NH3 conversion during the NH3 oxidation experiment In particular, compared to 3Cu/SAPO-34, NOx conversion over 3Cu-1Fe/SAPO-34 catalyst decreases slightly at low temperatures (below 200 °C), then an increase is observed in the range of 200 – 600 °C Notably, the NOx removal yields still reached 85% at 600 °C, indicating that 3Cu-1Fe/SAPO-34 catalysts have enlarged the 15 operating temperature window Clearly, high temperature activity was further improved due to the synergistic effects between Cu and Fe species 3.4 A comparison catalysts performance between metals-based SAPO-34 and metals-based ZSM-5 In the same strategy with SAPO-34, the ZSM-5 commercial based will be exchanged with Cu and Fe for comparison removal NOx ability by NH3-SCR through catalysts performance, and give an evaluation for which catalyst shows the best activity The synthesis route of Cu and/or Fe supported commercial ZSM-5 was similar to metal-incorporated SAPO-34 Firstly, the effects of Cu, Fe, and codoping Cu-Fe supported on ZSM-5 zeolite to their catalyst properties and catalysts performance were clarified Secondly, a comparison catalysts performance for NH3-SCR of NOx between SAPO-34 based and ZSM-5 commercial based was conducted The prevalent diffraction peaks for commercial ZSM-5 can be simple to index into the standard parameters for MFI topology, suggesting that ZSM-5 does not destroy its original form during the process of aqueous ion-exchange and calcination Figure 3.21 XRD patterns of ZSM-5 and as-synthesized catalysts Table 3.6 Fe, Cu, and Na amounts obtained by ICP-OES and textural properties Catalyst Metal atomic BET Avg pore Pore (wt.%) surface dia (nm) vol area (m2/g) (cm3/g) Cu Fe Na ZSM-5 0.075 397 0.45 0.25 1Cu/ZSM-5 0.97 0.079 383 0.47 0.32 2Cu/ZSM-5 1.92 0.077 301 0.48 0.34 3Cu/ZSM-5 2.89 0.075 257 0.50 0.35 1Fe/ZSM-5 0.92 0.073 355 0.52 0.28 2Fe/ZSM-5 1.91 0.079 287 0.54 0.29 3Fe/ZSM-5 2.78 0.074 232 0.55 0.31 2Cu-1Fe/ZSM-5 1.98 0.92 0.079 339 0.49 0.35 1Cu-2Fe/ZSM-5 0.91 1.93 0.078 259 0.51 0.32 16 Figure 3.22 EPR spectra of catalysts measured at room temperature Compared to the mono-metal catalysts, EPR signals of bimetallic catalysts exhibit dominant axial signals from isolated Cu2+ sites This behavior suggests that a suitable content of iron could lead to the formation of a higher amount of isolated Cu2+ ions Moreover, increasing the amount of Fe loading in bimetallic in 1Cu2Fe/ZSM-5 catalyst could reveal the signals of isolated Fe3+ in tetrahedral coordination at g = 4.23 Figure 3.23 a) Conversion of NOx and b) selectivity of N2 and N2O concentration during standard NH3-SCR of Cu-Fe/ZSM-5 catalysts When corporation of both Cu and Fe into ZSM-5, 2Cu-1Fe/ZSM5 catalyst significantly enhance the NOx conversion in the broader temperature range of 200 – 600 °C The conversion of NOx over 2Cu-1Fe/ZSM-5 catalyst decreases marginally at low temperatures (below 200 °C), accompanied by a rise in the range of 200 – 600 °C Notably, the NOx removal yields still reached 78% at 600 °C, suggesting that Cu-Fe/ZSM-5 catalysts have expanded the operating temperature window 17 As expected, the simultaneously exchanged, mixed-cation of Fe and Cu catalysts showed activities that lied above the single ion exchanged catalysts In all cases, mixing the cations led to a wider temperature window which is desirable for applications It is interesting to Figure 3.24 NOx conversions versus note, the Cu–Fe/SAPO-34 temperatures over metals-based ZSM-5 showed the highest activities (dash line) and metals-based SAPO-34 than other catalysts in the large (straight line) temperature range, showing a synergistic effect of Cu and Fe So, this research will select metal(s) based SAPO-34 catalysts as representatives in the following studies, in which the water vapor and SO2 poisoning resistance, as well as hydrothermal stability of Cu, Fe and Cu–Fe exchanged SAPO-34 catalysts will be discussed in the further section 3.5 The stability of SAPO-34 based catalysts 3.5.1 Influence of hydrothermal aging on activity Figure 3.25 a) NOx conversion of Cu/SAPO-34 and Cu-Fe/SAPO-34 after hydrothermal aging with GHSV of 120000 h-1 and (b) XRD patterns of fresh and hydrothermal aging catalysts Compared to 3Cu/SAPO-34_750, both of Cu-Fe/SAPO-34 samples with two hydrothermal aging conditions show significantly higher NOx conversion, indicating that Cu-Fe/SAPO-34 is more robust and resistant to relatively harsh hydrothermal treatment than 18 Cu/SAPO-34 To be more specific, XRD patterns of the fresh and hydrothermal aging catalysts were performed That insignificant influence on the bimetallic catalyst indicates that the introduction of iron could help to stabilize the copper dispersion during the aging, which can also be observed in the XRD patterns of fresh samples 3.5.2 Water vapor and SO2 poisoning resistance Figure 3.26 NOx conversion over Cu/SAPO-34, Fe/SAPO-34 and Cu-Fe/SAPO-34 catalysts at 200 °C (left) and 300 °C (right) under GHSV of 70000 h-1 in the copresence of H2O + SO2 The Cu-Fe/SAPO-34 showed superior water and sulfur dioxide resistance, compared to Cu/SAPO-34, maybe because Fe supported onto the surface of catalysts, resulted in more exposure to SO2 H2Ocontaining gasses of Fe compounds Consequently, the reaction with SO2 and H2O became much more efficiently, and then the Cu active sites were protected It indicated that a strong synergistic effect existed between the iron in the framework and the surface Indeed, as our previous report, the addition of Fe promoted the dispersion of active components, which is related to the special surface area, the acid sites, the redox properties, etc., of catalyst Besides the interaction between Cu and Fe, the increase of Cu2+ was also the main reason for improving activity and sulfur resistance Meanwhile, the content of adsorbed oxygen increased, improving the activity and sulfur resistance at low temperatures 19 3.6 Structure-reactivity relationships and active sites 3.6.1 in-situ EPR investigations Figure 3.27 in-situ EPR spectra of a) Cu/SAPO-34 and b) Cu-Fe/SAPO-34 after NH3/He/NO+O2 adsorption at 200 °C Table 3.7 The proportions of various Cu2+ species from the EPR spectra after evacuation Sample Progress Cu species type I III IV Cluster CuPre-treated 18.29% 36.17% 45.54% NH3 treated [Cu(NH3)4]2+ = 53.97% 46.03% NO + O2 treated 23.81% 27.66% 48.53% 120K before 19.38% 39.46% 41.16% 120K after 14.62% 33.91% 51.47% Cu-FePre-treated 27.40% 33.07% 39.53% NH3 treated [Cu(NH3)4]2+ = 59.79% 40.21% NO + O2 treated 25.11% 31.92% 42.97% 120K before 28.39% 35.32% 36.29% 120K after 26.60% 33.54% 39.86% The profile (1) of both pretreated catalysts presents two kinds of Cu2+ species The Cu2+ species with g|| = 2.39, A|| = 91 G is assigned to the Cu site (I), meanwhile, the Cu2+ species with g|| = 2.32, A|| = 119 G represents the Cu2+ located in the 6MR sites with two aluminum T-sites as site (IV) After NH3 adsorption for 45 at 200 °C, almost isolated Cu2+ species disappears in the profile (2), this species can be assigned to copper ammine species [Cu(NH3)4]2+ as the super-hyperfine was formed by the unpaired electron of Cu couplings to 14N from ammonia Therefore, the process with NH3 just plays the role of transforming isolated Cu2+ to copper ammine species 20 The EPR spectra in profile (3) show an interesting phenomenon that two kinds of Cu2+ species have differences between two catalysts after NO + O2 saturation Two Cu2+ species, one with with g|| = 2.32, A|| = 119 G represents the Cu2+ complex on site (IV) in the 6MR with 2Al, and the new Cu2+ species with g|| = 2.36, A|| = 132 G in Cu/SAPO-34 sample, which is assigned to the Cu2+ site (III) species This result indicates that the Cu2+ location in the bimetallic sample is more reactivity than in the mono metallic one The contribution of different Cu2+ species from EPR spectra are calculated by using the software package Easyspin implemented in MATLAB The Cu-Fe/SAPO-34 sample has the higher content of active isolated Cu2+ species, which is relevant to the highest NOx conversion over this sample Additionally, the Cu-Fe/SAPO-34 has higher total content of isolated Cu2+ species together with the higher number of the isolated Cu2+ at site (I), as the results, the CuFe/SAPO-34 catalyst shows better NOx conversion than Cu/SAPO34 3.6.2 in-situ FT-IR investigations The main objective of this section was to investigate the nature and the reactivity of surface species, and to study the key intermediates and possible reaction pathways by in-situ FTIR spectroscopy The NH3 could be adsorbed on the Lewis and Brønsted acid sites, which represents to the Cu2+−(NH3) Figure 3.28 In-situ FT-IR spectra of all species and the hydroxyl of the catalysts obtained after pre-adsorption framework [−Si−OH−Al−], of 0.1 vol.% NH3/He and subsequent respectively Because the Cu2+ exposure to 0.2 vol% NO + vol.% site is the active site, adsorbed O2/He for 45 at 200 °C NH3 species should migrate from Brønsted acid sites to Lewis acid sites to participate in the SCR reaction 21 NO oxidation to NO2 plays a vital role in the formation of surface intermediate nitrate species for NH3-SCR Therefore, higher NO oxidation of Cu-Fe/SAPO-34 might enhance its catalytic activity Figure 3.29 In-situ FT-IR spectra of all catalysts recorded at 200 °C after 1) preadsorption of 0.2 vol.% NO/He for 30 min, then 2) 0.2 vol.% ppm NO + vol.% O2/He for 30 min, followed by dosing of 3) 0.1 vol.% NH3/He for 45 with a) 4000 – 1300 cm-1 and b) 2000 – 1300 cm-1 3.7 Proposal NH3-SCR mechanism over Cu-Fe/SAPO-34 catalyst Figure 3.30 Propose NH3-SCR mechanism over Cu-Fe/SAPO-34 catalyst Both Langmuir-Hinshelwood and Eley-Rideal mechanism at 200 °C most likely participate in the SCR reactions of Cu-Fe/SAPO-34 catalyst, whereas the Cu/SAPO-34 catalytic activity dominates over the Eley-Rideal mechanism Therefore, the possible reaction pathways were proposed In the temperature range of 200 – 350 °C, the NH3 oxidation reaction is negligible and the standard SCR reaction proceeds on the isolated Cu2+ sites The enriched isolated Cu2+ sites on sample CuFe/SAPO-34 contribute to the improved performance At 22 temperatures higher than 350 °C, especially higher than 450 °C, the NH3 oxidation reaction is important on Cu-SAPO-34 However, the incorporation of Fe reduces the amount of bulk CuO species on the surface, thus slow down the NH3 oxidation reaction These results have been identified with our previous research that the combination of iron solution and the Brønsted acid protons in Cu/SAPO-34 during preparation make the catalyst in an acidic aqueous environment, enabling the transformation of part of bulk CuO to the extraframework Cu2+ Figure 3.31 The NH3-SCR reaction state over Cu/SAPO-34 and Cu-Fe/SAPO-34 catalyst samples under different temperatures a) and b) catalyst at 200 – 350 °C, c) and d) catalyst above 350 °C Furthermore, the isolated Fe3+, which shows a high activity on SCR reaction but a negligible NH3 oxidation ability, further enhances the high temperature activity of sample Cu-Fe/SAPO-34 Hence, the reduced NH3 oxidation ability and the addition of the isolated Fe3+ active sites combine to improve the activity of the Cu-Fe/SAPO-34 sample CONCLUSIONS SAPO-34 molecular sieves were prepared by using the hydrothermal method with various combinations of Mor/TEA/TEAOH as OSDAs showed different physicochemical characteristics Moreover, the investigation of silica source from TEOS to LUDOX AS-30 have influenced on the optimal composition of OSDAs and characteristics of SAPO-34 The 23 preparation of SAPO-34 catalysts with mixture tri-template (molar ratios of Mor : TEA : TEAOH = 3 : 3 : 1) synthesis and TEOS as a silica source was proven to be effective and has economic advantages, which is suitable for NOx removal by NH3-SCR The Cu/SAPO-34, Fe/SAPO-34, and bimetal Cu-Fe/SAPO34 catalysts were synthesized via a liquid ion-exchange method, and their application for NH3-SCR reactions was investigated Co-doping of Cu-Fe into SAPO-34 (with wt.% Cu and wt.% Fe) led to higher catalytic performance and selectivity for NH3-SCR, caused by the synergistic impacts between iron and copper Since the α-Fe2O3 particles would block the pores of the Cu-Fe/SAPO-34, the NOx conversion in low-temperature range below 200 °C slightly dismissed Thanks to the raised amount of isolated active Cu2+ sites, the activity for the bimetal Cu-Fe sample in 200 – 350 °C upturned Besides, the less amount of surface bulk CuO species got, the more decrease the NH3 oxidation above 350 °C showed The enhanced SCR performance of Cu-Fe/SAPO-34 samples above 350 °C resulted from both the reduced NH3 oxidation activity and the additional oligomeric Fe3+ active sites A comparison catalysts performance between Cu-Fe/SAPO34 and Cu-Fe/ZSM-5 have performed In all cases, mixing the cations led to a wider temperature window which is desirable for applications It is interesting to note, the Cu–Fe/SAPO-34 showed the highest activities than other catalysts in the large temperature range, showing a synergistic effect of Cu and Fe onto SAPO-34 carrier The hydrothermal stability enhanced over Cu-Fe/SAPO-34 compared with Cu/SAPO-34 at 750 °C and 850 °C, while the improvement of catalysts with poisoning SO2 and water vapor also was observed via Cu-Fe/SAPO-34 catalyst at 200 °C and 300 °C The NH3-SCR mechanism over Cu-Fe/SAPO-34 catalyst is evaluated in this study The in-situ EPR obviously illustrates the Cu2+ is the active sites at 200 °C over Cu-Fe/SAPO-34 catalyst The NH3 could be adsorbed on Cu2+ sites and the hydroxyls and the Cu2+ species are the active sites, and the latter one’s store and supply NH3 species The in-situ FT-IR results suggested that both Brønsted and Lewis acid sites were involved in NH3-SCR Both Langmuir- 24 Hinshelwood and Eley-Rideal mechanism at 200 °C most likely participate in the SCR reactions of Cu-Fe/SAPO-34 catalyst, whereas the Cu/SAPO-34 catalytic activity dominates over the Eley-Rideal mechanism Therefore, the possible reaction pathways were proposed PUBLICATIONS OF THE DISSERTATION Doan Anh Tuan, Nguyen Ngoc Khang, Dam Le Quoc Phong, Vuong Thanh Huyen, Le Minh Thang, Pham Thanh Huyen (2018), “Influence of organic structure directing agents on the formation of SAPOs structure”, Vietnam Journal of Catalysis and Adsorption, Vol 7, Issue 3, Pp 87-91 Thanh Huyen Vuong, Anh Tuan Doan, Thanh Huyen Pham, Angelika Brückner (2018), “Development of low-temperature catalysts for the selective catalytic reduction of NOx with NH3: Review”, Vietnam Journal of Catalysis and Adsorption, Vol 7, Issue 3, Pp 2-11 Doan Anh Tuan, Nguyen Ngoc Khang, Dam Le Quoc Phong, Vuong Thanh Huyen, Le Minh Thang, Pham Thanh Huyen (2019), “Synthesis, characterization of high hydrothermally stable Cu/SAPO-34 and Fe/SAPO-34 prepared by ion-exchange method”, Vietnam Journal of Chemistry, Vol 57, Issue 2e1,2, Pp 276-283 Nguyen Ngoc Khang, Dam Le Quoc Phong, Dinh Van Khanh, Lam Huu Minh, Doan Anh Tuan, Pham Thanh Huyen (2019), “Effects of silica sources on the morphology and acid properties of SAPO-34 molecular sieves”, Vietnam Journal of Catalysis and Adsorption, Vol 8, Issue 2, Pp 1-6 Tuan Doan, Khang Nguyen, Phong Dam, Thanh Huyen Vuong, Minh Thang Le, Huyen Pham Thanh (2019), "Synthesis of SAPO-34 Using Different Combinations of Organic Structure-Directing Agents", Journal of Chemistry, Vol 2019, Article ID 6197527, 10 pages, DOI: 10.1155/2019/6197527 Doan Anh Tuan, Dam Le Quoc Phong, Nguyen Ngoc Khang, Vuong Thanh Huyen, Le Minh Thang, Pham Thanh Huyen (2019), “Cu–Mn bimetal catalysts based on SAPO-34 for NOx removal by NH3-SCR from diesel engine exhaust”, Vietnam Journal of Catalysis and Adsorption, Vol 8, Issue 4, Pp 116-122 Tuan Doan, Khang Nguyen, Phong Dam, Nga Pham, Quan Vu, Thanh Huyen Vuong, Thanh Huyen Pham, Minh Thang Le (2020), “Zeotype SAPO-34 Synthesized by Combination of Templates for the Gasification of Biomass”, Chemical Engineering & Technology, Vol 43, Pp 731-741 DOI: 10.1002/ceat.201900598 Tuan Doan, Phong Dam, Khang Nguyen, Thanh Huyen Vuong, Minh Thang Le, Thanh Huyen Pham (2020), “Copper-Iron Bimetal Ion-Exchanged SAPO-34 for NH3-SCR of NOx”, Catalysts, Vol 10, No 321, DOI: 0.3390/catal10030321 Nguyễn Hồng Lê, Đinh Văn Khánh, Doãn Anh Tuấn, Vương Thanh Huyền, Phạm Thanh Huyền (2020), “The synthesis of Cu/SAPO-34 catalysts and evaluation ability of NOx treatment by NH3-SCR with Cu/ZSM-5 catalyst using commercial ZSM5 as support”, Vietnam Journal of Catalysis and Adsorption, Vol 9, Issue 2, Pp 3441, DOI: 10.51316/jca.2020.026 10 Tuan Doan, Anh Dang, Dat Nguyen, Khanh Dinh, Phong Dam, Thanh Huyen Vuong, Minh Thang Le, Pham Thanh Huyen (2021), “Influence of Aluminum Sources on Synthesis of SAPO-34 and NH3-SCR of NOx by as-Prepared Cu/SAPO-34 Catalysts”, Catalysis in Industry, Vol 13, Pp 27–37, DOI: 10.1134/S2070050421010098 11 Tuan Doan, Anh Dang, Dat Nguyen, Thanh Huyen Vuong, Minh Thang Le, Huyen Pham Thanh (2021), "Hybrid Cu-Fe/ZSM-5 Catalyst Prepared by Liquid IonExchange for NOx Removal by NH3-SCR Process", Journal of Chemistry, Vol 2021, Article ID 5552187, 15 pages, DOI: 10.1155/2021/5552187 12 Tuan Doan, Anh Dang, Dat Nguyen, The Tran, Thanh Huyen Vuong, Minh Thang Le, Thanh Huyen Pham (2021), “The promotion effect of iron to Cu/ZSM-5 catalyst for NOx removal by NH3-SCR,” Vietnam Journal of Chemistry, Vol 59, Issue 6, Pp 935-942, DOI: 10.1002/vjch.202100020 ... 5Fe/ SAPO- 34 4.82 332 0.44 39.43 62.67 1Cu1 .36 Cu – 398 0.47 38.22 67.85 3Fe/ SAPO- 34 3.08 Fe 2Cu1 .95 Cu – 479 0.53 36.49 70.82 2Fe/ SAPO- 34 1.93 Fe 3Cu3 .01 Cu – 499 0.56 34. 71 74.87 1Fe/ SAPO- 34. .. SAPO- 34 797 0.75 34. 29 86.48 1Cu/ SAPO- 34 1.06 583 0.69 34. 77 75.06 3Cu/ SAPO- 34 3.02 501 0.60 35.64 72.29 5Cu/ SAPO- 34 5.02 357 0.47 36.76 67.68 1Fe/ SAPO- 34 1.01 555 0.65 34. 60 74.04 3Fe/ SAPO- 34. .. analysis of the catalysts Catalyst Cu species (%) Fe species (%) Cu2 + CuO Fe2 + Fe3 + 3Cu/ SAPO- 34 39.65 60.35 1Fe/ SAPO- 34 69.62 30.38 3Cu5 1.15 48.85 62.24 37.76 1Fe/ SAPO- 34 Figure 3.16 XPS results of