Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).Nghiên cứu phản ứng hydroformyl hóa ethylene với CO và CO2 sử dụng xúc tác tẩm chất lỏng ion SILPTiO2 và nano AuTiO2 (SiO2).
INTRODUCTION
LITERATURE REVIEW
Our current economy strongly depends on fossil based products, not only for fuels, but also for the chemical and goods industry Declining resources but simultaneously increasing energy and commodity demands are characteristic for the last and also coming decades (Figure 1.1) [12] However, technical options for mining as well as natural reproduction of these fossil resources, like natural gas, crude oil and coal are limited Furthermore, burning fossil fuel emited massive amount of CO2 in the atmosphere which is the main reason contributing to global warming, politicians started to take action against climate change; Therefore the European commission has set up an Energy Roadmap 2050 [13], in which they urged to transform the current economy into a “lowcarbon economy” and reduce
“greenhouse emission to 80-95% below 1990 levels”
Figure 1.1 Total world energy consumption by energy source, 1990-2040 (reproduced from [12])
This can be achieved by either capture/storage or utilization of this gas as a reactant for producing fuels or/and useful chemicals in an environmentally friendly manner [14] This is particularly valid when CO2 is converted into long-time stable and usable products like polymers, dyes, or resins, which are currently produced from ethylene and propylene The latter building blocks are currently generated from fossil carbon-containing feedstock through strongly endothermic cracking reactions resulting in large CO2 emissions [15] As CO2 conversion into value- added alcohols and hydrocarbons requires H2, the production of the latter should also meet the requirements for environmental compatibility Water splitting powered through solar and/or wind energy is a suitable option [16] Propanal is an important chemical produced on a large scale over homogenous Co- or Rh- containing catalysts through hydroformylation of C2H4 using H2 and CO as
14 additional reactants This aldehyde can be further hydrogenated to propanol, which is one of the basic chemicals used in daily life [17].Various heterogenous catalysts were also applied for gas-phase hydroformylation of ethylene to propanal [17,18]
However, all hydroformylation processes suffer from the usage of toxic CO at high pressure as well as decreased activity with increasing time on stream because of leaching of catalytically active species [19] These drawbacks can be overcome with the idea of using CO2 instead of CO and/or applying alternative catalysts In this regard, the group of Kondratenko developed supported Au-based catalysts for the direct conversion of CO2 with H2 and C2H4 into propanol with near to 100% selectivity to this alcohol with respect to CO2 [20] This could be a very prospective utilization of CO2 for a more sustainable liquid hydrocarbon manufacturing in future This chapter, hydroformylation of ethylene with using of CO or CO2 will discuss in detailed The catalysts for hydroformylation process focused on the two kinds of novel Supported Ionic Liquid Phase – SILP catalysts and gold-based catalysts
The development of green catalyst routes to synthesize commercially important chemicals is an environmentally and economically beneficial effort Green chemistry involves designing, developing and implementing chemical products and processes to reduce or eliminate the use and production of hazardous substances to human health and the environment It's an innovative, non-regulatory, economically-oriented approach to sustainability Green technology is getting considerable attention as awareness of environmental issues has increased The concept of environmentally-friendly product and process design is expressed in the 12 “Green Chemical Principles” as follows [21]
1 Waste prevention instead of remediation 2 Atom efficiency
3 Use of less hazardous/toxic chemicals 4 Design safer chemicals and products 5 Use innocuous solvents and reaction conditions 6 Design energy efficient processes
7 Preferably renewable raw materials 8 Shorter synthesis route and avoid derivatization 9 Use catalyst instead of stoichiometric reagents 10 Design products for degradation after use 11 Real time analytical methodologies for pollution prevention 12 Inherently safer processes to minimize the potentials for accidents Catalysis plays an important role in the production of diverse products, with applications in medicines, plastics, agricultural chemicals, perfumes, detergents, food, clothing, fuels, etc [22] In addition, it plays an important role in the ecological and environmental balance by providing cleaner alternatives to stoichiometric technologies
The green catalyst process efficiently uses all raw material atoms, removes waste and
15 avoids the use of toxic and/or hazardous reagents and solvents in the manufacture and application of chemical products
Hydroformylation is an important commercial process for converting alkenes, carbon monoxide and hydrogen into aldehyde for further use in the production of various chemicals Industrial processes operate in a homogeneous medium Thus, the development of a solid catalyst will solve the problems associated with catalyst separation and thus contribute to the reduction of waste from these chemical processes
In this regard, the creation of new hydroformylation catalyst production is concerned as green chemistry
Hydroformylation is one of the oldest and largest homogeneously catalyzed reactions of olefins The reaction was first discovered in 1938 by Roelen [23] while working for Ruhrchemie in Germany Roelen investigated the effect of added olefins to cobalt catalysts and identified aldehydes as one of the oxygen containing components
H2 and CO can add across the double bond of olefins to form aldehydes in the presence of a Co (or Rh) catalyst
The process is frequently referred to as the “Oxo” process, with Oxo being short for Oxonation, i.e the addition of oxygen to a molecule However, the term hydroformylation is descriptively more accurate and more useful in characterizing this type of reaction catalyzed by various transition metal complexes because during the reaction a hydrogen atom and a formyl group are added to the olefinic double bond
Figure 1.2 Depiction of hydroformylation of olefins [21]
The relative amounts of normal- and branched-chain aldehydes produced depend on the identity of R and other constituents of the reaction mixture
Normal-chain aldehydes, the more desirable products, usually are hydrogenated, affording straight-chain alcohols, or self-condensed, affording more complex aldehydes
Figure 1.3 Products derived from aldehydes manufactured by hydroformylation [24]
16 With a terminal alkene as substrate, the normal/branched ratio is an important parameter in the industrial hydroformylation process; generally rule, the better catalytic performance, the higher the ratio, although significant markets have developed for the branched aldehydes In addition to linear terminal olefins, a wide variety of different olefins have been successfully hydroformylated, e.g linear internal olefins, unsaturated alcohols, phenols, ethers, and amides [24]
1.1.1 Commercial demand of hydroformylation products
The oxo process or hydroformylation of olefins with synthesis gas is the principal route to C3-C15 aldehydes, which are converted to alcohols, acids, or other derivatives By far the most important oxo chemical is n-butyraldehyde, followed by C6-C13 aldehydes for plasticizer alcohols, isobutyraldehyde, propionaldehyde, valeraldehyde, and C12-C18 aldehydes for detergent alcohols Propylene-derived n- butyraldehyde and isobutyraldehyde accounted for approximately 77% of the world consumption of oxo chemicals in 2021
Figure 1.4 World consumption of oxo chemicals in 2021 (Source: IHS Market) [25]
High consumption volumes for both of the alcohol derivatives of n- butyraldehyde, n-butanol and 2-ethylhexanol (2-EH) will continue in the near future, largely owing to increased consumption of both alcohols in acrylate esters, acetate esters, and plasticizers 2-EH and n-butanol continue to account for the majority of plasticizer alcohols consumption, combining for three-quarters of the global total The pie chart (Figure 1.4) shows world consumption of oxo chemicals:
Asia, Europe, and North America are the largest markets for oxo chemicals, together accounting for 95% of world demand in 2021 Oxo chemicals demand in mainland China is expected to grow relatively well, albeit at a slower growth rate than in previous years Other Asian consumption, excluding mainland China and Japan, is also expected to grow well; India and Malaysia are the main growth markets in this region Demand for oxo chemicals in the United States is expected
17 to grow modestly during 2021–26 Western European consumption of oxo chemicals is forecast to also grow modestly, as will Japanese consumption
By far, most oxo aldehydes are hydrogenated to alcohols The large majority of the world consumption of n-butyraldehyde is converted to 2-EH and n-butanol, while all of the detergent and C7-C13 plasticizer oxo aldehydes are converted to their corresponding alcohols Other oxo chemicals, including propionaldehyde, valeraldehyde, and isobutyraldehyde, have more varied applications As a result, demand for oxo chemicals is strongly dependent on demand for C4-C13 plasticizer alcohols Consumption of plasticizer alcohols, especially C7-C13 alcohols, depends greatly on demand for plasticizers and flexible PVC Growth in the world consumption of plasticizer alcohols for plasticizers is forecast at 3.2% annually during the next few years Solvent/coating applications are the largest end use for C4-C5 alcohols; this includes direct solvent use and derivative solvent use, mainly as acetates, glycol ethers, and acrylates
The Oxo Alcohol Market Size was valued at USD 14.3 Billion in 2022 [26] The Oxo Alcohol market industry is projected to grow from USD 14.98 Billion in 2023 to USD 20.1 Billion by 2030, exhibiting a compound annual growth rate (CAGR) of 5.2% during the forecast period (2023 - 2030) The market for oxo-alcohols was chiefly driven by escalating demand from the plasticizers as well as the solvents industry Increasing demand for plasticizers from their end-user industries has been the key factor for driving the Oxo Alcohols Market during the forecast period
MO - ] where + and MO - represent the positive and negative surface sites,
The PZC measurements of synthetic oxides were widely conducted using MT technique The MT technique was developed by Noh and Schwarz (1989) to estimate the PZC of simple oxides [114] The dry oxide must be a pure mineral
41 phase and is assumed to be uncharged When it is put into pure water, the pH of the suspension changes and the final pH value depends on the oxide concentration The suspension reaches a constant value after the addition of an excess of solid This limiting pH value can be interpreted as a function of the solid concentration according to: where Nt is the total number of ionizable sites on the mineral surface (it is representative of the mass of the solid); (COH - CH) is the difference between the concentration of OH - and H + in the mineral suspension, and is therefore representative of the pH of the suspension; [MOH2 +], [MOH], and [MO - ] are the concentrations of positive, neutral, and negative sites, respectively
From equation 1.8, as Nt approaches infinity and (COH - CH) ≠ 0 (the case when the suspension pH is not equal to 7), [MOH2 +] - [MO - ] approaches 0 Under these conditions, the net surface charge of the solid is zero and the PZC value is reached
If the PZC of the oxide is 7 (as is the initial pH of pure water) the suspension pH will not change with increasing mineral mass In such a case (COH - CH) = 0 and the pH is independent of the mass (Nt)
Table 1.3 Point of Zero Charge (PZC) values of various solid oxides [115]
MgO 12.1 a, g, h a Precipitated product b Natural product c Ignited precipitate d PZC determined on silver powder. e PZC by electrophoresis f PZC by streaming potential g PZC by electroӧsmosis h PZC by absorption of potential-determining ions
Table 1.3 showed PZC values of some popular solid supports used for synthesis of gold supported catalysts A decreasing difference in electronegativity between the oxygen and M atom should correlate with an increasing tendency
42 toward acid dissociation of the MOH group According to this criterion the PZC values for MO2 oxides should increase in the order:
SiO2 < SnO2 < ZrO2 < TiO2 because the electronegativity differences increase from 1.7 for SiO2 to 6.0 for TiO2
The goal of this research was to develop a solid catalyst for heterogeneous hydroformylation of ethylene with CO and/or CO2 as two different feedstocks
Rhodium is the most active transition metal for hydroformylation and it was the obvious choice for the catalytic Rh-complexes in the preparation of the SILP catalysts Water-soluble phosphine ligands TPPTS-Na3 was chosen and preparation via sulfonation of Triphenylphosphine Ionic Liquid [BMIM][n-C8H17OSO3] was used based on previous studies [8,9] For the supports, TiO2 was chosen mainly, because it is an inert, stable and almost neutral support material widely applied in catalysis, other support like SiO2 was chosen as well The roles of supports were also expected to be clarified In particular, the surface acidity of the supports might affect oxo selectivity as well as the deactivation of catalyst was also indicated
Supported nano gold particles were chosen as catalyst for hydroformylation of C2H4 using CO2 as a new feedstock for directly conversion of CO2, H2 and C2H4 to propanol, propanal (oxo products) TiO2, SiO2 supports were selected to evaluate the effects of different supports on NP Au particle’s dispersion Point of zero charge (PZC), surface acidity, surface area, pore structures etc can affect scattering of Au particle active sites and catalytic performance that were also expected to be discussed Modification of Au/SiO2 catalysts were investigated by introducing transition metals to gold supported SiO2 substrate to obtain bimetallic catalyst in order to improve catalytic activity
Hence, these new catalysts based on Rh- supported ionic liquid phase (SILP) and nano gold particles on TiO2, SiO2 supports were prepared, characterized and activity-tested Compositions of the catalysts were also altered in order to investigate the influences of Ionic Liquid contents on the catalytic activities Both catalysts (SILP and supported Au catalyst) were tested for hydroformylation of ethylene with CO and/or CO2 as feedstocks
Moreover, this thesis also focused on finding the solutions to over come the drawback of thermodynamic barriers in direct conversion reaction of CO2, H2, C2H4 into propanol using the new idea about a “dual-reactor” system in which the total process can be separated into two single processes that optimized the reaction temperature of the RWGS process and the Hydroformylation process, thereby resolving thermodynamic obstacles and improving catalyst’s performance
EXPERIMENTALS
2.1.1 Synthesis of SILP catalysts a Preparation of tri-(m-sulfophenyl)-phosphine (TPPTS) ligand:
Triphenylphosphine-3,3’,3’’-trisulfonic acid trisodium salt (TPPTS-Na3) was used as ligand in the SILP catalysts In this section, the synthesis of ligand TPPTS-Na3 is described
(i) The following chemicals were used:
Fuming sulfuric acid/oleum (H2SO4.xSO3), (30%,Merck);
Sodium hydroxide monohydrate (NaOH.H2O) (95%, Aldrich);
TPPTS-Na3 was synthesized at the laboratory as following procedure:
P(C6H5)3 + 3SO3 (H2SO4) P(C6H4SO3H)3 (2.1) P(C6H4SO3H)3+ 3N(C8H17)3 [HN(C8H17)3]3[P(C6H4SO3)3] (2.2) [HN(C8H17)3]3[P(C6H4SO3)3] + 3NaOH P(C6H4SO3Na)3+ 3N(C8H17)3 (2.3) Diagram of the ligand synthesis is illustrated in Figure 2.1 Whole process was performed in N2 atmosphere or vacuum using a Schlenk system: 96 g of oleum (30 wt.%) was placed in a 250-ml flask equipped with a stirrer, thermometer, dropping funnel, and cooler and was cooled to an internal temperature of 15°C Over a period of one hour, 10.5 g (40 mmol) of triphenylphosphine and a further 32 g of 30 wt % oleum was added with stirring After the addition of oleum and triphenylphosphine had completed, the mixture was stirred for 150h at 20°C Subsequently, the mixture was added to a flask containing 300g of water having a temperature of about 10°C
During the addition, the internal temperature was kept between 20°C and 40°C by external cooling
The homogeneous sulfonation mixture was placed in a flask and stirred with a mixture of 47.7 ml (110 mmol) trioctylamine and 180 ml toluene After the addition was completed, the reaction mixture was stirred for an additional 30 min and then left to separate for 30 mins The lower phase (water containing acid and impurity) was separated and discarded
An aqueous sodium hydroxide solution (5 %) was added to the toluene solution with stirring until the mixture reached a pH of 5.5 (the aqueous solution which contains mainly TPPMS, TPPDS and minor amounts of oxide product) The
44 aqueous solution was separated and discarded The addition of base to toluene phase was continued until the mixture was reached to a pH of 5.5-6.5 The aqueous solution was separated By concentration of the aqueous solution, the crude yellow solid of product can be obtained
Figure 2.1 Setup for the synthesis of Ligand TPPTS
Methanol and water (100 ml of a 10:1 mixture) was used to dissolve the Sodium salt of 3,3’,3’’-phosphinetriylbenzensulfonic acid The reaction mixture was heated to reflux for 30 min, followed by filtration while the solution was hot Upon cooling to room temperature, pure white crystalline solid of product was obtained For the synthesis of ligand TPPTS-Cs3, the procedure is the same but CsOH was used instead b Preparation of TiO2 support
Tetraisopropyl orthotitanate C12H28O4Ti (TTIP) 98%, Merck, Germany;
Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) PEG-PPG-PEG (P123), Aldrich, Germany;
Acid citric monohydrate C6H8O7.H2O, 98% China; Acid sulfuric 98%, China;
Distillated water; Isopropanol 99%, China (IPA) (ii) Procedure: Mesoporous titania support were prepared by hydrothermal crystallization method follow this procedure: Solution A is prepared by adding 50 ml of alcohol isopropylic and 12.5 ml of TTIP which is further stirred for 20 min to gain a homogeneous solution
45 Solution B is prepared by mixing of 100 ml alcohol isopropylic and 100 ml distillated water Afterward, 4 grams of P123 was slowly added with stirring to dissolve completely in order to gain homogeneous solution Finally, 0.8 ml solution of sulfuric acid 98% and 2.15 g of citric acid were added and stirred for 1 hour more Then solution B is slowly added into solution A with stirring to reach a stable suspension sol solution The sol solution was settled in 50 o C for 2 hours Then the sol solution was crystallized in autoclave at 90 o C for 20 hours Products was filtered and dried at 120 o C then calcinated at 450 o C (rate of 2 o C/min) for 4 hours in order to gain white powder c Preparation of SILP catalysts
Ionic Liquid: [BMIM][n-C8H17OSO3] (98%, Merck), (BMIM = 1-butyl-3- methylimidazolium) with free halidales, friendly environment was chosen to use in this study
Support: mesoporous TiO2 which was prepared by hydrothermal method as described above
Active phase: Rh(CO)2(acac)( Dicarbonyl-acetylacetonato-rhodium(I): (98%, Aldrich)
Rh(CO)2(acac) Solvent: MeOH (99%, Merck) Before using, MeOH must be distilated very carefully with molecular sieve 4A in order to get the absolutely dried methanol
Synthesis procedures: The Schlenk system to synthesize catalysts is illustrated in Figure 2.2 Schlenk tubes were pre-dried in ovens prior to use Prior to coming into an inert atmosphere, vessels are further dried by purge-and-refill procedure: the vessel is subjected to a vacuum to remove gases and water, and then refilled with inert gas This cycle is usually repeated three times or the vacuum is applied for an extended period of time The purge-and-refill is applied directly to the reaction vessel through a hose or ground glass joint that is connected to the manifold
Figure 2.2 The Schlenk system to synthesize of catalysts
46 The precusors (ionic liquid, ligand and Rh(CO)2(acac)) were weighed precisely and put together in a Schlenk vessel (A vessel) This vessel was purged and refilled three times in order to remove all of air in the free space
Dry MeOH was transferred using of a syringe from another schlenk vessel to the A Meanwhile, nitrogen was flushed through a stopcock in both of vessels, MeOH was taken out as well as filled in slowly by a syringe through a rubber septum
After stirring the A vessel for 20-30 mins by a magnetic stirrer, a yellow solution was formed The synthesized TiO2 anattas support was put in a B schlenk vessel
Purge and refill was done also with the B one Transfer the solution from A to B by a syringe Continuously stir for 30 mins MeOH was removed by rotary distillation in vacuum overnight using a rotatory evaporator A fine powder was formed, called SILP (Supported Ionic Liquid Phase), and was kept in decicator under inert gas pressure The obtained powder was light yellow Summary of all catalyst samples were synthesized in this thesis is presented in table 2.1
Table 2.1 Summary of synthesized SILP catalysts
(mol/mol) content IL (%V pore) content Rh (%w)
IL=2,5_TiO 2 TPPTS-Na 3 TiO 2 10 2.5 0.2
IL=5,0_TiO 2 TPPTS-Na 3 TiO 2 10 5.0 0.2
IL,0_TiO 2 TPPTS-Na 3 TiO 2 10 10 0.2
IL,0_TiO 2 TPPTS-Na 3 TiO 2 10 10 0.2
IL,0_SiO 2 TPPTS-Na 3 SiO 2 10 10 0.2
IL=2,5_TiO 2 TPPTS-Cs 3 TiO 2 10 2.5 0.2
IL=5,0_TiO 2 TPPTS-Cs 3 TiO 2 10 5.0 0.2
IL,0_TiO 2 TPPTS-Cs 3 TiO 2 10 10.0 0.2
2.1.2 Preparation of supported nano gold catalysts
Nano-sized gold particles were believed to be a prospective catalyst to convert alkene into oxo products In our research, supported Au nanoparticles catalysts were prepared on some support materials etc TiO2, SiO2
2.1.2.1 Preparation of Au/TiO2 catalysts using different methods
0,5Au_TiO2 catalysts were synthesized by different methods listed in table 2.2, the samples were assigned as 0,5Au_TiO2_QTx, where “x” stands for method of synthesis The aim of this investigation is to find the best procedure which could adjust and control the particle-size of gold on support
47 Deposition–precipitation procedure (denoted as QT1):
0,5Au_TiO2 QT1 was synthesized by deposition–precipitation (DP) of gold hydroxide from HAuCl4 (41.1 wt% Au, Chempur) on the support as follows:
2 grams of as synthesized TiO2 support were added at room temperature under continuous stirring to a 0.314 mM HAuCl4 solution (200 ml) and further stirred for 20 min Afterwards, NH3 solution (25%) was slowly added until pH 10.5 was reached After 10 min aging phase, the solid was filtered, washed to remove Cl - ion, and finally dried in air at 80 o C to yield gold supported catalysts
Table 2.2 Summary of synthesized Au/TiO2-based catalysts using different methods
Sample code Synthesis method Au loading weigh [%wt] [a]
0,5Au_TiO2 QT2 Hydrothermal 0.5 0,5Au_TiO2 QT3 DP-vaporized 0.5
0,5Au_TiO2 QT4 Sol-gel 0.5
[a]: Au loading weigh % content determined by theory
Hydrothermal procedure (denoted as QT2):
0,5Au_TiO2 QT2 was prepared by hydrothermal method in which gold hydroxide and titanium hydroxide were co-precipitated from a mixed solution of 0,314 mM HAuCl4 (200ml) and 10 ml of Titanium(IV) isopropoxide (Merck) diluted in 100 ml of iso-propanol and adding of 2,06 grams of P123 which is using as template The solution was then added Na2CO3 (5%) solution in order to gain final pH of 9 Finally, the obtained solution was then treated by hydrothermal method at 90 o C in autoclave for 3 days Products were filtered, washed to remove Na2CO3 and then calcinated in air at 450 o C to yield Au/TiO2 catalyst
Deposition–precipitation and vaporizing procedure (denoted as QT3):
RESULTS AND DISCUSSIONS
3.1 Characterization of TPPTS ligands 3.1.1 IR spectra of TPPTS ligands
Figure 3.1 FT-IR spectra of TPPTS-Cs3 and TPPTS-Na3 ligands
Synthesized TPPTS-Na3 ligands in this study was IR analysized and the obtained results were compared to the IR spectrum of the TPPTS-Cs3 sample Both TPPTS- Cs3 and TPPTS-Na3 ligands were synthesized at the same pH range of 5.5-6.5
TPPTS-Na3 ligand was synthesized at the same route of TPPTS-Cs3, in which, NaOH solution of 5% was used to replace for CsOH solution in eq.2.3 The IR spectra of TPPTS-Cs3 ligand and TPPTS-Na3 ligand were shown in Figure 3.1 The vibrations of O–H at 1640cm -1 and 3400cm -1 were belong to water, due to the adsorption of moisture from environment The vibration of C–H was seen from 2800 – 3000cm -1 Almost the vibration of the sulfonic groups (SO3) at 1200 cm -1 , 1100 cm -1 and 1050 cm -1 were obtained on both ligands, especially, the peak at 1200cm -1 was very strong identified to sulfonic groups One medium peak at 620 cm -1 which was belong to vibration of S-O which surely confirmed the appearance of sulfonic group This suggested that the sulfonization of TPP has successfully introduced the sulfonic groups to the original TPP molecule The peak at 1641cm -1 assigned to P-C vibration could obtained clearly that confirmed the original structure of the TPP remained stable after the sulfonization Characteristic vibrations of C-H at 993, 817, 799, 792 cm -1 from the phenyl groups and the vibration at 690 cm -1 from Triphenylphosphine disulfonate (TPPDS) could be
75 observed in both spectra of TPPTS-Cs3 and TPPTS-Na3 Therefore, it showed that TPPTS-Na3 ligand and TPPTS-Cs3 was successfully synthesized by using NaOH and CsOH
To better compare the performance of synthetic ligands (TPPTS-Na3) in comparison to that of the TPPTS-Cs3 ligands, both ligands were used to synthesize SILP catalysts on the same type of TiO2 support
3.1.2 1 H – MAS NMR and 31 P – MAS NMR characterization
In order to obtain more information about TPPTS-Na3 ligand, the ligands are continued to be measured in 1 H – MAS NMR and 31 P – MAS NMR characterization spectra The NMR 1 H spectra (Figure 3.2) show that ligand TPPTS-Na3 & TPPTS- Cs3 only have -OH of H2O at chemical shift of 4.8 ppm This can be explained by ligand adsorption of water from the environment The chemical shift of 3.4 ppm is characterized of H in aromatic cycles
Figure 3.2 1 H – MAS NMR spectrum of synthesized TPPTS-Cs(b) 3 ligand (a) and TPPTS-Na3 ligand (b).
76 Ligand TPPTS is known to be easily oxidized under the synthesis condition because O2 (in air) could get inside the synthesis system by somehow although inert gas was purged during the procedure Moreover, the ligands are gradually, but slowly, oxidized to the corresponding phosphine oxides when they are handled in air Even upon storage under dry conditions in vacuo, some degradation by oxidation took place over time The oxidation of the ligand from TPPTS form to OTPPTS form will lead to the significant decrease of catalytic activity because OTPPTS is inactive form Therefore NMR is the perfect method in order to evaluate the quality of ligand before using since TPPTS and OTPPTS form appear separately as two distinguish peaks at 4.2 and 29.5 ppm (chemical shift), respectively, in 31 P MAS NMR spectra
(b) Figure 3.3 31 P-MAS NMR spectrum of synthesized TPPTS-Cs3 ligand (a) and
The 31 P MAS NMR spectrum of the as synthesized TPPTS-Cs3 ligand and TPPTS-Na3 ligand which were used to synthesize SILP catalysts are shown in
77 Figure 3.3 The spectrum (Figure 3.3 a) shows only one sharp peak at 29.6 ppm, which is assigned to the OTPPTS form which revealed that TPPTS-Cs3 oxidized completely to phosphine oxides which is inactive ligand Fortunately, figure 3.3b demonstrated NMR spectrum of synthesized TPPTS-Na3 ligand in a good quality
This spectrum showed two peaks at -4.2 and 29.5 ppm, which are straightforwardly assigned to TPPTS (active) and OTPPTS (inactive), respectively Due to the presence of a large amount of TPPTS form (about 60 % as calculated from peak ratio between δ (-4.2)/ δ (29.5) is 60/40) in this ligand, this ligand was then used in preparation of SILP catalysts For the TPPTS-Cs3 ligand, we also use it for the synthesis process of SILP as a comparision sample for the studies
3.2.1 BET, dispersion and ICP-EOS characterization
The Brunauer−Emmett−Teller specific surface areas (SBET) of bare TiO2 support and different percent of IL loading catalytic samples are listed in Table 3.1
Table 3.1 Summary of synthesized SILP catalysts and their properties
The TiO2 support was prepared successfully as mesoporous materials with pore size of 100 A o and pore volume of 0.279 cm 3 /g As increasing the loading amount of ionic liquid content results in decreasing much surface area of catalysts (from 107 m 2 g -1 as bare TiO2 support decreased to 25 m 2 g -1 for the sample with 10 percents of ionic liquid loading) As the results show, a small amount of ionic liquid loading (2.5% volume) could lead to reducing surface area significantly from 106.7 m 2 /g of TiO2 to 44.69 m 2 /g of SILP catalyst We believe that ionic liquid has quickly covered the pore structure of TiO2 since almost pore structure in TiO2 support were micro pores which is lower than 50A o This explanation was logic as we can see the gradually decrease in surface area when increase in percent of ionic liquid loading When the small pores were covered by ionic liquid, it is obviously
0.2%Rh-2.5%IL- L/Rh/TiO2, TPPTS-Na3
0.2%Rh-5%IL- L/Rh/TiO2, TPPTS-Na3
0.2%Rh-10%IL- L/Rh/TiO2, TPPTS-Na3
0.2%Rh-10%IL- L/Rh/TiO2, TPPTS-Cs3
0.2%Rh-5%IL- L/Rh/TiO2, TPPTS-Cs3
0.2%Rh-2.5%IL- L/Rh/TiO2, TPPTS-Cs3
78 seen that the pore distribution was increasing, because the large pores were still remained
The pore distribution of TiO2 support and SILP catalysts with different IL loading are presented in Figures 3.4 - Figures 3.8
Figure 3.4 Isotherm and pore distribution of TiO2 support
Figure 3.5 Isotherm and pore distribution of 0,2Rh-L/Rh, IL=2.5%-TiO2 catalyst with
Figure 3.6 Pore distribution of 0,2Rh-L/Rh, IL=5%-TiO2 (a) and 0,2Rh-L/Rh,
IL%-TiO2 (b) catalysts with TPPTS-Cs3 ligand
79 Figure 3.7 Isotherm and pore distribution of 0,2Rh-L/Rh, IL=2.5%-TiO2 catalyst with
Surface area and dispersion (as calculated by (Eq 2.15)) of 0,5Au_TiO2 catalysts synthesized by different methods are listed in table 3.2
Table 3.2 0,5Au_TiO2 catalysts and their selected physicochemical properties
Sample code Synthesis method Au loading weigh [%wt] a
0,5Au_TiO2 QT3 DP-vaporized 0.5 4.30 26 99.04
0,5Au_TiO2 QT4 Sol-gel 0.5 0.05 2437
[a]: Au loading weigh % content determined by theory
[b]: Dispertion of Au NP active sites calculated by CO pulse chemisorption (followed Eq 2.15)
[c] d Au-NP stands for the size of gold clusters were calculated according to the equation from theory of CO pulse chemisorption (using Equation 2.17)
Figure 3.8 Isotherm and pore distribution of SILP catalysts (a) 0,2Rh-L/Rh, IL=5%-
TiO2 and (b) 0,2Rh-L/Rh, IL%-TiO2 with ligand TPPTS-Na3
80 The calculated results revealed the 0,5Au_TiO2 QT3 sample possess the smallest nanoparticle-size of 26 nm, vice versa, other samples had very large particle sizes of about several hundreds nanometer Although the calculation of Au particle size from CO pulse chemisorption may not really precise and could be influenced by other measuring factors, it may still be an evidence to compare particle size of Au in different synthesized samples It was very odd when 0,5Au_TiO2 QT4 sample (sol- gel prepared one) has very large Au particle size of 2437 nm The reason for that, which was suggested by us, could be the sintering in consequences gold sites were covered by TiO2 This was logical when the dispersion of gold on this sample was very low (0.0465%)
The sample 0,5Au_TiO2 QT1 was prepared by DP method which was referred as a very good method to prepared Au NP on TiO2 but the particle size was quite large (333nm) We claim that the Au weigh content was lower than that of theory since gold compound still diluted in aquatic phase then the washing products lead to remove gold out of sample Therefore, we suggested preparation of the 0,5Au_TiO2 QT3 without the washing step instead by heating to vaporize the water
It is worth mentioning that the dispersion of Au sites much increased from 0.34% to 4.3%
Gold clusters were deposited on the TiO2 support from solution of HAuCl4 using NH3 solution to precipitate Au(OH)3 at pH about of 10.5 It is necessary to wash the sample after deposition and remove the chloride without leaching gold
However, the point of zero charge (PZC) of TiO2 is about 6, so this washing step could be the reason for leaching gold since the adsorption of gold anions (as AuCl4 -) on oxide supports is only possible in the case the pH of the solution is lower than PZC of the TiO2 We believed that 0,5Au_TiO2 QT1 and 0,5Au_TiO2 QT2 samples which were washed by distillated water had lower gold contents than that of 0,5Au_TiO2 QT3 and 0,5Au_TiO2 QT4 without washing steps The dispersion of Au on TiO2 support results from CO pulse chemisorption could give the same evidence The 0,5Au_TiO2 QT3 has the highest DAu (4.30%) because of conservation of Au on the TiO2, otherwhile, the Au_TiO2 QT1 has only DAu of 0.34
% which is believed of leaching Au from washing step It is also odd to mentioning that the Au_TiO2 QT4 has much low DAu of 0.05% even without washing step of preparation It is suggested that using the sol-gel method the gold clusters were covered inside of TiO2 support Therefore, we suggest using deposition – precipitation (DP) method without washing step but instead by heating to vaporize water phase to yield Au_TiO2 catalyst (that we described in QT3 procedure) as the ameliorated method in order to prevent the leaching gold
The experimentally determined values of the Au/SiO2 catalysts synthesized by DP method are given in Table 3.3 The elemental analysis by ICP-OES revealed that Au loading slightly deviated from the theoretical one (the number before Au in the catalyst symbol) probably due to the loss of HAuCl4 in the filtrate The Cesium content almost corresponds to the theoretical loading since the deposition of Cs was performed by an incipient wetness impregnation method without filtering
81 Table 3.3 Prepared Au/SiO2 and Cs Au/SiO2 catalysts and their BET surface area values (SBET) , Au average crystallite size (d Au NP) prepared catalysts Au loading (wt%) (a) loading Cs (wt%) (b) dAu NP
(a) Au content was determined from ICP-OES For lower 1%Au content, ICP-OES could not determine
(b) Cs content was determined from AAS (c) Average crystallite size was calculated from the corresponding reflection at 38.2° using the Scherrer equation (2.12)
(d) Specific surface area of catalyst measure before carrying out the reaction
(e) Specific surface area of catalyst measure after carrying out the reaction
CONCLUSIONS
The present study has demonstrated the preparation, characterization and performance of novel heterogeneous catalysts for hydroformylation of ethylene with CO or CO2 and H2 over SILP catalysts and Au-containing supported catalysts like Au/TiO2 and Au/SiO2
For the traditional hydroformylation of C2H4 with CO and H2, the study focused on two kind of catalyst SILP over TiO2 supports and nano Au particles supported over TiO2 The following main conclusions obtained from the research:
Heterogeneous C2H4 conversion with CO and H2 to propanol/propanal was first demonstrated over Au/TiO2 catalysts in a single continuous-flow reactor
Catalysts showed activities above 200 o C Au active sites impacted significantly to catalytic activities, nano size Au particles (26 nm) showed better activity than micro-size one (2437 nm) However, catalytic performance was very low in comparison with that of traditional Rh-complexes SILP catalysts
The Au_TiO2 catalysts were prepared by different methods which demonstrated that the DP method with heating vaporization instead of washing step could help to prevent leaching gold but remaining nano-sized particles (26 nm)
Therefore, the 0,5Au_TiO2 sample prepared by that method shows good selectivity of propanol
SILP/TiO2 synthesized with TPPTS-Na3 ligand (containing 60% of the active form) was evaluated to be active in the hydroformylation reaction of ethylene The results showed that the amount of loading ionic liquid much depends on the pore size and pore volume of support The 2.5 percent ionic liquid content is optimal with TiO2 supports, the optimal reaction temperature is 120 o C
The deactivation of activity of the SILP catalytic after long-time reaction was first demonstrated by the EPR spectrum, suggesting that the catalyst's degradation of the Rh-TPPTS complexes led to the loss of the ligand
For the second route, the study demonstrated that performing heterogeneous conversion of C2H4 with CO2 and H2 to propanal/propanol over Au/SiO2 catalysts according to a dual-reactor approach is an attractive option for improving the selectivity to the desired products From the prospective results obtained, the following conclusions as shown:
Heterogeneous C2H4 hydroformylation with CO2 and H2 to propanal/propanol was for the first time demonstrated over SiO2 supported Au- containing catalyst in a new reactor system included two continuous-flow reactors that is so-called “dual-reactor” The prospective results showed that the oxo- selectivity based on ethylene has increased up to ca 60%
1wt% of Au loading over SiO2 has the best catalytic activities since Au NP was formed with average size of 6nm that is believed as the optimal Au NP size which promoted the hydroformylation of ethylene Otherwise, the Au NP size of larger than 10nm or lower than 4nm were not active for hydroformylation but promoted the hydrogenation of C2H4 to C2H6
The doping Cs on Au supported catalyst was not helpful, conversely, catalyst was less active because Cs blocks active sites on Au NP, as well as, Cs caused the decrease of surface area of catalyst The promoter has a strong negative effect on the conversion, which decreases from 13 to 2.7% at 175 °C or from 30 to 3% at 200°C with an increase in Cs loading from 0 to 2 wt %
Introducing transition metal to Au based supported SiO2 carrier as bimetallic catalyst did not cause a positive effect on catalytic activity, on the contrary, it also created a risk of sintering Au clusters and significantly decrease in catalyst activity
Using a single-bed reactor, ethane was identified to be the main product in the hydroformylation of ethylene with CO2 over 1Au/SiO2 at 175 and 200°C The conversion of ethylene is near to complete Product selectivity and conversion of ethylene change strongly when performing the hydroformylation of ethylene according to a dual-reactor approach The conversion is only 13 and 30% at 175 and 200 °C, respectively, in comparison with 100% in the single-bed reactor These results clearly demonstrate the potential of dual-bed reactor approach for the production of propanal/propanol using a feed containing ethylene, carbon dioxide, and hydrogen.
Based silica supports like SiO2, SBA-15 seem be suitable supports for Au supported nanoparticles It can be explained since SiO2 possesses negatively charged in aqueous solution that is favorable for cationic gold species in synthesis process.
New contribution of the thesis:
Studies have shown that the effects of the surface acidic properties of
TiO2 and SiO2 supports have only minor effects on the activity of the catalyst due to the formation of the aldols products, which indicated that catalyst activity is strongly dependent on the pore size, the pore volume and the surface area of the catalysts.
Au/TiO2 catalysts were active for traditional C2H4 hydroformylation reactions with H2 and CO However, its activity is much lower than that of a catalyst based on the Rh complexes of SILP/TiO2.
For the first time, C2H4 hydroformylation took place with a substitute
CO2 reactant for a traditional CO reactant based on an Au/SiO2 catalyst for remarkable activity with oxo products selectivity of 60% and ethylene yield of 13% at 175 o C.