Danny S. Brands

The relation between reduction temperature and activity in copper catalysed ester hydrogenolysis and methanol synthesis.

Zinc and manganese promoted silica supported copper catalysts show an activity increase in methyl acetate hydrogenolysis and methanol synthesis after high temperature reductive treatments. The effect of reduction can largely be reversed by applying a treatment in an inert atmosphere at reduction temperature, which results in a decrease in copper surface area as measured by N2O chemisorption and which is accompanied by distinct changes in the XRD pattern of the catalyst. These phenomena could be explained with a model assuming the reversible formation of epitaxial, two-dimensional, copper particles on top of a mixed oxide phase.

The relation between pre-treatment of promoted copper catalysts and their activity in hydrogenation reactions

The influence of reduction temperature on promoted and unpromoted silica supported copper catalysts in ester hydrogenolysis and methanol synthesis from CO/H 2 and CO 2 /H 2 mixtures was investigated. Results on ester hydrogenolysis using model methyl acetate feed could be confirmed with a more realistic feed such as methyl palmitate. Zn and Mn proved effective promoters in ester hydrogenolysis. After high temperature reduction of promoted catalysts a remarkable increase in activity was observed for all reactions studied. In ester hydrogenolysis this effect renders the Cu/Zn/SiO 2 catalyst superior to a commercial Cu/Cr reference. The effect of high temperature reduction is explained by a previously proposed model involving formation of epitaxial twodimensional platelets of reduced copper on top of a mixed oxide. These sites are able to activate CO towards CH 3 OH formation, in contrast to unpromoted Cu/SiO 2 or low temperature reduced Cu/Zn/SiO 2 .

Permanganic acid: a novel precursor for the preparation of manganese oxide catalysts

Unsupported and ψ-alumina supported MnO x catalysts (1–10 wt-% Mn) were preparedfrom aqueous solutions of HMnO 4 and compared with nitrate based samples. They were characterized by XRD, XPS, BET area, oxygen storage capacity and by their catalytic behaviour versus ammonia DeNO x reaction. The unsupported oxide is amorphous at 300°C with a high surface area (45 m 2 .g −1 ) and transforms to α-Mn 2 O 3 below 600°C. The supported samples show high dispersion which correlates well with high catalytic activity and the absence of detectable crystalline phase. The difference between HMnO 4 and manganese nitrate precursors vanishes after calcination at 1000°C, with the formation of Mn 3 O 4 and the transformation of the carrier into α-alumina; the DeNO x activity remains high but the selectivity towards N 2 decreases as the temperature increases.

Methanol decomposition on unpromoted and Zn promoted Cu/SiO2 catalysts

The decomposition of methanol over promoted and unpromoted copper containing catalysts has been investigated. The reaction rate over unpromoted Cu/SiO2 is constant with increasing catalyst reduction temperature, whereas the ZnO promoted catalyst showed a strong decrease in activity, accompanied by an enhanced selectivity to methyl formate. FT-IR experiments showed that at reaction temperature methoxy species are stabilised on the high temperature reduced Cu/ZnO/SiO2 catalyst. Since stabilisation of these species at 470 K only occurs on oxidised copper, this suggests that copper cations are present in the high temperature reduced catalysts. Combining these results with earlier findings on methanol synthesis, it is proposed that the newly formed sites are located at the Cu-ZnO interface. At this interface, ionic copper is stabilised.