Methanol synthesis reaction mechanism

The hydrogenation of carbon dioxide produced iso-butane over Fe-Zn-M/HY (M= Al, Cr, Ga, Zr) composite catalysts with high selectivities. The mechanism of iso-butane formation combines the methanol synthesis reaction and the MTG reaction. The olefins were formed to be important intermediates for iso-butane formation. In order to obtain high selectivity of iso-butane, we found it essential to prepare a composite catalyst which has high activity for methanol synthesis but low activity for the hydrogenation of olefins. 

The mechanism of methanol synthesis from syngas over Pd catalysts has been studied with Ca-doped Pd catalysts supported on silica.90 It was found that basic metal oxides are needed to give a Pd catalyst with high activity for methanol formation. The authors proposed that the Ca-doped Pd/SiC>2 catalysts acted as a bifunctional catalyst in the methanol synthesis reaction. Sites on the metal oxide are responsible for the formation of the formate... 

A microkinetic analysis of the methanol synthesis reaction has recently been performed [7,8]. The starting point for the analysis is that the active phase for methanol synthesis is metallic copper. The following mechanism based on primarily surface science studies over Cu single crystals was proposed ... 

Example 6.11.5 Kinetic mechanism of the methanol synthesis reaction catalyzed with Cu/Zn0/Al20j/Zr02 (developed by Lim et al., 2009)... 

Because the synthesis reactions are exothermic with a net decrease in molar volume, equiUbrium conversions of the carbon oxides to methanol by reactions 1 and 2 are favored by high pressure and low temperature, as shown for the indicated reformed natural gas composition in Figure 1. The mechanism of methanol synthesis on the copper—zinc—alumina catalyst was elucidated as recentiy as 1990 (7). For a pure H2—CO mixture, carbon monoxide is adsorbed on the copper surface where it is hydrogenated to methanol. When CO2 is added to the reacting mixture, the copper surface becomes partially covered by adsorbed oxygen by the reaction C02 CO + O (ads). This results in a change in mechanism where CO reacts with the adsorbed oxygen to form CO2, which becomes the primary source of carbon for methanol. 

Methanol synthesis served as the model for the true mechanism. Stoichiometry, thermodynamics, physical properties, and industrial production rates were all taken from the methanol literature. Only the reaction mechanism and the kinetics of methanol synthesis were discarded. For the mechanism a four step scheme was assumed and from this the... 

Remarks The aim here was not the description of the mechanism of the real methanol synthesis, where CO2 may have a significant role. Here we created the simplest mechanistic scheme requiring only that it should represent the known laws of thermodynamics, kinetics in general, and mathematics in exact form without approximations. This was done for the purpose of testing our own skills in kinetic modeling and reactor design on an exact mathematical description of a reaction rate that does not even invoke the rate-limiting step assumption. 

To facilitate the use of methanol synthesis in examples, the UCKRON and VEKRON test problems (Berty et al 1989, Arva and Szeifert 1989) will be applied. In the development of the test problem, methanol synthesis served as an example. The physical properties, thermodynamic conditions, technology and average rate of reaction were taken from the literature of methanol synthesis. For the kinetics, however, an artificial mechanism was created that had a known and rigorous mathematical solution. It was fundamentally important to create a fixed basis of comparison with various approximate mathematical models for kinetics. These were derived by simulated experiments from the test problems with added random error. See Appendix A and B, Berty et al, 1989. 

The reaction mechanism of methanol synthesis is complex since two processes are involved and coupled. Formally, the reaction can be written as the hydrogenation of CO by the overall reaction ... 

Figure 8.3 Proposed reaction mechanism for methanol synthesis on Pd and comparison with gas-phase mechanism surface intermediates are speculative and associated energies are estimates...

Mechanisms for both reactions are proposed, which are supported by the identification of several intermediate reactions. The role of various organic and inorganic reaction promoters is discussed. Amongst these, phosphine oxides are exceptionally efficient in that they induce high reaction rates combined with high selectivities. Reactions a) and b) potentially allow two-step, methanol/ /synthesis gas-based routes to ethyl acetate and proprio-nic acid, respectively. 

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 ... 

Although numerous investigations have been performed on methanol synthesis catalysts, the structure of the active catalysts, the nature of the active sites, and the reaction mechanism are still subjects of considerable controversy. 

The mechanism of CH4 oxidation with hydrogen peroxide shown in Figure 5.4 assumes proceeding of several radical-chain reactions of methanol synthesis. In analyzing kinetic equations (5.31)—(5.35) the following inequalities were deduced ... 

The oxidation mechanism should be interpreted in the context of the conjugated reaction theory. For this purpose, the overall equation of the methanol synthesis secondary reaction was deduced by combining the elementary stage of PPFe3+OOH/AlSiMg intermediate formation (7.13) and the elementary stage (7.14) ... 

S-i Fujita, Bhanage BM, Ikushima Y et al (2001) Synthesis of dimethyl carbonate from carbon dioxide and methanol in the presence of methyl iodide and base catalysts under mild conditions effect of reaction conditions and reaction mechanism. Green Chem 3(2) 87-91... 

Vollmuller F, Krause J, Klein S, Magerlein W, Beller M (2000) Palladium-catalyzed reactions for the synthesis of fine chemicals, 14 - control of chemo- and regioselectivity in the palladium-catalyzed telomerization of butadiene with methanol - catalysis and mechanism. Eur J Inorg Chem 1825-1832... 

Gas feeds for industrial methanol synthesis usually contain both CO and C02. Which carbon oxide serves as the primary source for methanol formation has been arguably the most important question pertaining to the reaction mechanism. Early work by Klier and coworkers assumed that CO was the primary source, and that the active site consisted of Cu+ species dissolved in ZnO. However, Klier s model... 

Many studies of simultaneous adsorption of hydrogen or water and CO or C02 have been carried out on the high-pressure methanol synthesis catalysts based on zinc oxide and one or several other oxides, but only three investigations (104, 113, 114) dealt with catalysts containing copper, and two of these were made in reference to the mechanism of the low-temperature shift reaction. 

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