Palladium catalysts methanol synthesis

Bimetallic (98) and alloy catalysts (97), of interest for hydrogenation reactions, have been investigated in in situ characterizations of methanol synthesis from CO and H2 in the presence of novel Cu-Pd alloy catalysts supported on carbon the results show surface segregation of palladium on the catalyst particles in CO atmospheres, but surfaces with equal amounts of copper and palladium when the atmosphere is H2 (97). 

Palladium and rhodium based catalysts, which yield methanol and ethanol from synthesis gas respectively, were selected for a mechanistic study. Chemical trapping showed a correlation between formyl species and the catalytic activity, indicating that these species probably are reaction intermediates. The role of the support on the activity and on the nature of the products was elucidated by chemical trapping of formyl, methoxy and formate species on palladium catalysts, and of formyl and acetate on rhodium catalysts. The rhodium catalysts were also studied by probe molecule experiments CH CHO) and by FT-IR spectroscopy (chemi-... 

Copper based catalysts have long been considered as the only effective methanol synthesis catalysts. However, Poutsma et al. (7) showed that palladium catalysts were active in methanol synthesis from CO-H. This latter metal had been previously considered as either almost inactive or active only for methane formation (8). Furthermore it is now known that both activity and selectivity can change drastically with the support. Vannice (9) observed that the methanation activity of a Pd/Al O was enhanced eighty and forty times compared to palladium black or Pd/SiO (or Pd/TiO ) respectively. The support effect on the selectivity was pointed out by many authors even at atmospheric pressure when the reaction temperature... 

These results suggest clearly that, on palladium catalysts, formyl and methoxy species are reaction intermediates in the methanol synthesis from CO-H. No significant changes were observed in the concentration of formate species, thus they are believed to play no role in the methanol synthesis on these catalysts. 

Among the transition metals, Pd, Pt, Ir, and Rh in various forms have been reported active in methanol synthesis (32-34), as noted in Section II. Palladium, platinum, and iridium metals were supported on silica, and it has recently been suggested that palladium is present in its valence state Pd(II) which is the active form of the catalyst (70). Under the synthesis conditions the Pd(II) ions could not survive the highly reducing atmosphere of the CO/H2 synthesis gas, and so this valence state would have to be induced by the presence of silicon dioxide. Should this be a general case, silica would not act merely as an inert support, and the silica-supported transition metals would have to be considered binary catalysts whose active state is formed by a support-metal interaction. ... 

Methanol adsorption and decomposition on noble metals have been the subject of many surface-analytical investigations (e.g., References 94,171,320,350,378, 478 94). CH3OH dehydrogenation on palladium catalysts could be a valuable source of synthesis gas or hydrogen, but unfortunately catalyst deactivation by carbon deposits (coking) seriously limits this process (495-498). In this respect, the probability of O H vs. C O bond scission is important, the first path resulting in CO and H2, and the second in carbon or carbonaceous species (CH x = 0-3), CH4, and H2O (see scheme in Fig. 49 details are discussed below). 

Syngas conversion to methanol has been shown to take place on supported palladium catalyst [1]. Methanol can in turn be converted to gasoline over ZSM-5 via the MTG process developed by Mobil [2]. In recent work we have reported syngas (CO/H2) conversion to hydrocarbon products on bifunctional catalysts consisting of a methanol synthesis function, Pd, supported on ZSM-5 zeolites [3]. Work on syngas conversion to hydrocarbon products on Pd/SAPO molecular sieves has been published elsewhere [Thomson et. al., J. CataL. in press].Therefore, this paper will concentrate on propylene conversion. 

Hydrogenation of Dinitrotoluene to Toluenediamine. The hydrogenation of the dinitrotoluene mixture to toluenediamines is once again a standard process in aromatic synthesis. This reaction can be carried out with iron and aqueous hydrochloric acid like the reduction of nitrobenzene, but catalytic hydrogenation is preferred (e.g., in methanol with a Raney nickel catalyst at about 100°C and over 50 bars, or with palladium catalysts). 

Because of the strong coordination of sulfur to metal surfaces, sulfur-containing molecules are very effective catalyst poisons. Nevertheless, a few examples of the hydrogenation of such molecules have been reported. Thiophene can be hydrogenated to tetrahydrothiophene by use of rhenium heptasulfide [44] under harsh conditions (250 °C and 300 atm hydrogen) or with a large excess of palladium in methanolic sulfuric acid [45]. In the synthesis of biotin, stereoselective civ-hydrogenation of a tri-substituted thiophene was achieved with Pd/C in acetic acid [46]. 

M.L. Poutsma, L.F. Elek, P. Ibarbia, H. Risch, and J.A. Rabo. Selective Formation of Methanol from Synthesis Gas over Palladium Catalysts. J. Catal. 52 157 (1978). 

In addition, LagOg is a particularly attractive support because it affords high selectivity and specific activity in the methanol synthesis reaction. LagOg-modified palladium catalysts have been reported to be very active for the synthesis of methanol from (CO -I- Hg)... 

A two step synthesis of ( )-eucomol (10) has been published by Farkas et al. 23, 24). 5,7-Di-O-benzyleucomin (43) was transformed with alkaline hydrogen peroxide to the 3.9-epoxy compound (44). Hydrogenation with a special palladium catalyst under carefully controlled conditions led to (10) in moderate yield. Proof for structure (44) was adduced by boiling the compound with p-toluenesulfonic acid in methanol which gave the 9-methoxy derivative (45). 

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