Structure control on kinetics of copper reduction in Zr-containing mixed oxides during catalytic hydrogenation of carbon oxides to methanol

A series of coprecipitated binary Cu-ZrO2 catalysts was found to show an interesting activity-selectivity pattern during methanol synthesis from catalytic hydrogenation of carbon oxides (PR, 20-30 atm; TR, 200-240 °C). The effects of various pre-treatments as well as the copper/zirconia ratio on the structural and chemical properties of these samples were examined. The isoconversional Ozawa-Flynn-Wall method was applied to study the reduction behaviour, while the best fit modelling was used to establish the plausible mechanism of copper reduction. The extent of methanol formation rate was found to be dependent on the structure formed upon catalyst reduction, both in CO and in CO2 hydrogenation conditions. The pre-calcination of the sample at a temperature as high as 650 °C negatively affected the methanol formation rate under CO hydrogenation conditions, while under the same activation treatment an increased specific activity was observed in CO2 hydrogenation conditions, although with a minor methanol selectivity, since the rate of the WGS reaction was stronger enhanced. The incorporation of Zn into the catalyst formulation resulted in a visible increasing of the methanol formation rate, owing to the formation of a copper-zinc mixed oxide during calcination, which leads to higher metal dispersion also depressing the methane formation rate.