Methanol synthesis from CO2 and

Development of high performance Raney copper-based catalysts for methanol synthesis from CO2 and H2... 

As it was reported in others works [6], the increase in copper surface area could be related to the formation of smaller copper particles on the surface of Raney copper due to the slower rate of leaching when the zincate is present. Therefore, both the nature of precursor alloy and the nature of leaching solution were found to be key factors in the preparation of high performance Raney Cu for methanol synthesis from CO2 and H2. 

Figure 2. Flow diagram of a 50 kg/day test plant for methanol synthesis from CO2 and H2 The reaction conditions were as follows reaction tube of 38.4 mmID x 4 mL, catalyst loading = 0.5-3 1, temperature = 503-543 K, pressure = 3-11 MPa,...

Methanol synthesis from CO2 and H2 has received much attention as one of the most promising processes to convert C02 into chemicals. Gas-phase methanol synthesis process should recycle a large quantity of unconverted gas and furthermore the single pass conversion is limited by the large heat release in the reaction. Liquid-phase methanol synthesis in solvent has received considerable attention, since temperature control is much easier in the liquid phase than in the gas phase. 

GaUucci F, Basile A. A theoretical analysis of methanol synthesis from CO2 and in a ceramic membrane reactor. Int J Hydrogen Energy 2007 132 5050-5058. 

Saito, M., Takeuchi, M., Fujitani, T., Toyir, (., Luo, S., Wu, (., Mabuse, H., Ushikoshi, K., Mori, K., and Watanabe, T. (2000) Advances in joint research between NIRE and RITE for developing a novel technology for methanol synthesis from CO2 and H2. Appl. Organomet. Chem., 14, 763-772. 

Scheme 7.31 Surface reactions involved in the methanol synthesis from CO2 and the corresponding elementary and rate-determining steps (RDS)...

Raudaskoski R, Niemela MV, Keiski RL (2007) The effect of ageing time on co-precipitated Cu/ZnO/Zr02 catalysts used in methanol synthesis from CO2 and H2. Top Catal 45 57-60... 

Kenji U, Kozo M, Takeshi K, Taiki W, Masahiro S (2000) Methanol synthesis from CO2 and H2 in a bench-scale test plant. Appl Organomet Chem 14 819-825... 

Figure 8.14. Turnover frequency for methanol synthesis from H2 and CO2 at 18 bar and 523 K as a function ofZn coverage on polycrystalline copper. [From j. Nakamura, I. Nakamura,...

Methanol Synthesis from CO2 Thermodynamic and Kinetic Considerations... 

Yang YX, et al. Fundamental studies of methanol synthesis from CO2 hydrogenation on Cu(lll), Cu clusters, and Cu/Zn0(0001). Phys Chem Chem Phys. 2010 12(33) 9909-17. 

The methanol generation from CO2 and H2 was carried out in a bench scale synthesis plant with a reactor voliune of about 400 ml. A modified Cu/CuO based catalyst (C79-05-GL of... 

The mechanism and kinetics of methanol synthesis over Cu have been the subjects of extensive investigations [1-3]. Despite considerable research, there still remain controversies as to the exact mechanism by which methanol is synthesized over Cu-based catalysts and very little is agreed upon concerning the nature of active site and the role of ZnO phase. The present work was undertaken to obtain a more detailed mechanism of methanol synthesis from CO2/H2 over Cu/ZnO/Si02. To do this in situ FTIR was to observe the structure and surface concentration of adsorbed species during the reaction. Complementary TPD studies were also conduced to analyze the surface species. 

Today methanol has become a very important feedstock for the production of many chemicals. Use as a clean fuel has increased and methanol is used in the production of the popular oxygenated fuel additive, MTBE. It has also been postulated that methanol could be a carrier of energy for safe transportation between remote countries. Furthermore, to prevent a greenhouse effect caused by COj generated from the tremendous oxidation reactions on the earth, methanol synthesis from CO2 is regarded as one of the potential solutions to decrease CO2 by the reaction with hydrogen which is produced by electrolysis of water, for example. Due to the increasing demand for methanol, many researchers are involved in the development of more active methanol synthesis catalysts. 

Fujita et al. have prepared different precursors that have the same ratio Cu/Zn=5/5 and have measured their activities for methanol synthesis from CO2 conversion under ambient pressure at 440 K. As shown in Table 3, the catalyst prepared from the pre-... 

Jia, L., Gao, J Fang, W and Li, Q. (2012) Influence of copper content on structural features and performance of pre-reduced LaMni 4,Cue03 (0-o l) catalysts for methanol synthesis from CO2/H2. /. Rare Earths, 28, 747-751. 

Scheme 7.30 Mechanism of methanol synthesis from CO2/H2 and CO/CO2/H2 over ultrafine CuMn0/Al203 catalyst [293]...

Based on the thermodynamic evaluation by Bonura et al. [217], the conversion of methanol to DME on the acidic zeolite sites rapidly approaches the equilibrium level at all the investigated temperatures because it is a fast reaction. Moreover, they also observed a promoting effect of the reaction temperature on the relative rate of methanol synthesis from CO2 rather than CO, on the basis of thermodynamics. Hence, based on their findings, the authors have proposed the reaction in Scheme 7.32. It turns out that, apart from the methanol dehydration reaction, 3 which takes place very fast at any temperature, reactions 1-2-4 affect the methanol formation depending on their relative reaction rates. The thermodynamic analysis of the main reaction paths involved in the synthesis of DME by CO2 hydrogenation reveals that, under kinetic conditions, the CO concentration dramatically increases with temperature therefore, low reaction temperamre and recycling unreacted COx/H2 mixtures could be a solution to improving the methanol/DME productivity. 

Schilke TC, Fisher lA, Bell AT (1999) In situ infrared study of methanol synthesis from CO2/ H2 on titania and zirconia promoted Cu/Si02. J Catal 184 144—156... 

Sloczynsky J, Grabowski R, Kozlowska A, Olszewski P, Lachowska M, Skrzypek J, Stoch J (2003) Effect of Mg and Mn oxide additions on structural and adsorptive properties of Cu/ZnO/Zr02 catalysts for the methanol synthesis from CO2. Appl Catal Gen 249 129-138... 

Chinchen, G.C., Denny, P.J., Parker, D.G., and Spencer, M.S. Mechanism of methanol synthesis from CO2/CO/H2 mixtures over copper/zinc oxide/alumina catalysts — use of C-14 labeled reactants. Appl Catal 1987, 30, 333-338. 

MeliSn-Cabrera, 1., Lopez Granados, M., and Fierro, J.L.G. Reverse topotactic transformation of a Cu-Zn-Al catalysts during wet Pd impregnation relevance for the performance in methanol synthesis from CO2/H2 mixtures. J. Catal 2002, 210, 273-284. 

Non-metallic homogeneous catalyst systems were also reported for methanol synthesis. Recently, Ashley et al. [49] demonstrated the selective hydrogenation of COj to methanol using a FLP-based nomnetal mediated procedure at low pressures (1-2 atm). N-Heterocyclic carbine (NHC) was found to be an elFective organic catalyst for methanol synthesis from CO2 reduction with silane. Compared to transition metal catalyst, NHC is more efficient at ambient reaction conditions [50,51]. Table 5.1 lists catalytic activities of different heterogeneous catalysts employed for methanol synthesis from CO. It shows that maximum CO conversion of 25.9%, methanol selectivity of 99.5% and methanol yield of378 mg/g-cat h could be achieved. The space velocities were tried between 1800 and 18,000 h and the temperature from 170 to 270 C. 

This is illustrated by the TPD spectra of formate adsorbed on Cu(lOO). To prove that formate is a reaction intermediate in the synthesis of methanol from CO2 and H2, a Cu(lOO) surface was subjected to methanol synthesis conditions and the TPD spectra recorded (lower traces of Fig. 7.13). For comparison, the upper traces represent the decomposition of formate obtained by dosing formic acid on the surface. As both CO2 and H2 desorb at significantly lower temperatures than those of the peaks in Fig. 7.13, the measurements represent decomposition-limited desorptions. Hence, the fact that both decomposition profiles are identical is strong evidence that formate is present under methanol synthesis conditions. 

The solution is illustrated in Fig. 8.15, which shows the equilibrium concentration of methanol for different initial gas mixtures. Note that the maximum methanol concentration occurs for the pure CO + H2 mixture. Hence, in principle, a mixture of just CO and H2 could be used, with minor amounts of CO2, to produce the maximum amount of methanol. However, it is not only the equilibrium constant that matters but also the rate of methanol formation, and one must remember that methanol forms from CO2 not CO. Hence, the rate is proportional to the CO2 pressure and this is why the methanol synthesis is not performed with the simple stoichiometric 3 1 mixture of H2 and CO2 that Eq. (19) suggests. 

Recent research on the catalytic synthesis of methanol from CO2 and H2 over a copper catalyst has shown that the rate of reaction is first order in CO2 and 3/2 in H2. 

The mechanism for methanol synthesis from mixtures of H2, CO and CO2 over supported Cu catalysts have been studied extensively in the literature using a number of chemical methods (Bell et al 1995). One of the key issues has been the role of CO and CO2 in maintaining the carbon supply for methanol synthesis or interconversion betwen the two via the water-gas shift reaction ... 

Unpromoted Cu/Si02 is found to have a low activity for methanol synthesis from H2/CO mixtures, whereas an increased activity from H2/CO2. Alkali metal promotion increases the activity for methanol synthesis from the H2/CO mixtures, probably due to the increase in surface OH groups engaged in the formation of the formate species which are the precursors to the methanol. Cu/Si02 powder catalysts (with 5 wt% Cu) can be prepared by ion exchange of silica with Cu(NOs)2 in aqueous solution, followed by calcination and reduction. Such preparations contain very fine Cu particles ( 0.5 nm) on a powdered silica support as revealed by HRTEM. 

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