Methanol surface science

Catalysis and Surface Science Developments in Chemicals from Methanol, Hydrotreating of Hydrocarbons, Catalyst Preparation, Monomers and Polymers, Photocatalysis and Photovoltaics, edited by Heinz Heinemann and Gabor A. Somorjai... 

In this chapter, we have summarized (recent) progress in the mechanistic understanding of the oxidation of carbon monoxide, formic acid, methanol, and ethanol on transition metal (primarily Pt) electrodes. We have emphasized the surface science approach employing well-defined electrode surfaces, i.e., single crystals, in combination with surface-sensitive techniques (FTIR and online OEMS), kinetic modeling and first-principles DFT calculations. 

A paper by Szanyi and Goodman [56] on the synthesis of methanol over a copper single crystal provides a good example of how AES is often used in surface science studies of catalytic reactions. These authors investigated the formation of methanol from a mixture of CO2, CO and H2 on Cu(100) at tempera-... 

This section reports a series of examples of application of the cluster model approach to problems in chemisorption and catalysis. The first examples concern rather simple surface science systems such as the interaction of CO on metallic and bimetallic surfaces. The mechanism of H2 dissociation on bimetallic PdCu catalysts is discussed to illustrate the cluster model approach to a simple catalytic system. Next, we show how the cluster model can be used to gain insight into the understanding of promotion in catalysis using the activation of CO2 promoted by alkali metals as a key example. The oxidation of methanol to formaldehyde and the catalytic coupling of prop)me to benzene on copper surfaces constitute examples of more complex catalytic reactions. 

The adsorption of CO is probably the most extensively investigated surface process. CO is a reactant in many catalytic processes (methanol synthesis and methanation, Fischer-Tropsch synthesis, water gas shift, CO oxidation for pollution control, etc. (1,3-5,249,250)), and CO has long been used as a probe molecule to titrate the number of exposed metal atoms and determine the types of adsorption sites in catalysts (27,251). However, even for the simplest elementary step of these reactions, CO adsorption, the relevance of surface science results for heterogeneous catalysis has been questioned (43,44). Are CO adsorbate structures produced under typical UHV conditions (i.e., by exposure of a few Langmuirs (1 L = 10 Torrs) at 100—200 K) at all representative of CO structures present under reaction conditions How good are extrapolations over 10 or more orders of magnitude in pressure Such questions are justified, because there are several scenarios that may account for differences between UHV and high-pressure conditions. Apart from pressure, attention must also be paid to the temperature. 

K.1.1. UHV Investigations of Pd( 111) under Adsorption/Desorption Conditions. A classical surface science approach to the surface reactions of methanol involves adsorption of methanol at cryogenic temperatures and monitoring of changes upon... 

The surface science studies of methanol oxidation over metals were carried out under conditions where no (y) oxygen was present on the surfaces. A temperature-programmed reaction experiment was performed [49] in order to... 

The experiments have shown that mechanistic aspects discussed in the surface-science literature of methanol oxidation are of relevance under high-pressure high-temperature conditions. Surface science has provided the techniques and fundamental insight into species present on metal surfaces. The remote reaction conditions do not allow the assignment of the stable intermediates which were spectroscopically characterized as the reaction intermediates. Experiments at conditions closer to practical conversion have revealed a novel oxygen species and cast doubt on the relevance of a stable methoxy species for catalysis. 

Control of reaction paths on catalyst surfaces by optimizing the structure and electronic properties is a key issue to be solved in surface science. Iron/molybdenum oxides are used as industrial catalysts for methanol oxidation to form formaldehyde selectively. The iron /molybdenum oxide catalyst consists of Fe2(Mo04)3 and M0O3, and shows kinetics and selectivity similar to those of M0O3 for methanol oxidation [Ij. It suggests that Mo-O sites play an important role in the reaction. M0O3 has a layered structure along a (010) plane, but the (010) surface is not reactive because it has no unsaturated Mo site [1]. On Mo metal surfaces such as (100) [2,3] and (112) [4], major products in methanol reactions were H2 and CO. Therefore, we considered that partial oxidation of Mo sites is needed for the selective oxidation of methanol. We have reported that methanol reaction pathways on Mo(l 12) could... 

Schulz, H., W. Bohringer, W. Baumgartner and Z. Siwei, 1986, Comparative investigation of time on stream selectivity changes during methanol conversion on different zeolites, in New Developments in Zeolite Science and Technology, eds Y. Murakami, A. Iijima and J.W. Ward, Vol. 28 of Studies in Surface Science and Catalysis (Elsevier, Amsterdam) pp. 915-922. 

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