Physico-Chemical Modifications Affecting the Activity and Stability of Cu-Based Hybrid Catalysts during the Direct Hydrogenation of Carbon Dioxide into Dimethyl-Ether

The direct hydrogenation of CO2 into dimethyl-ether (DME) has been studied in the presence of ferrierite-based CuZnZr hybrid catalysts. The samples were synthetized with three different techniques and two oxides/zeolite mass ratios. All the samples (calcined and spent) were properly characterized with different physico-chemical techniques for determining the textural and morphological nature of the catalytic surface. The experimental campaign was carried out in a fixed bed reactor at 2.5 MPa and stoichiometric H-2/CO2 molar ratio, by varying both the reaction temperature (200-300 degrees C) and the spatial velocity (6.7-20.0 NL center dot g(cat)(-1)center dot h(-1)). Activity tests evidenced a superior activity of catalysts at a higher oxides/zeolite weight ratio, with a maximum DME yield as high as 4.5% (58.9 mg(DME)center dot g(cat)(-1)center dot h(-1)) exhibited by the sample prepared by gel-oxalate coprecipitation. At lower oxide/zeolite mass ratios, the catalysts prepared by impregnation and coprecipitation exhibited comparable DME productivity, whereas the physically mixed sample showed a high activity in CO2 hydrogenation but a low selectivity toward methanol and DME, ascribed to a minor synergy between the metal-oxide sites and the acid sites of the zeolite. Durability tests highlighted a progressive loss in activity with time on stream, mainly associated to the detrimental modifications under the adopted experimental conditions.

Automated summary

The direct hydrogenation of CO2 into dimethyl-ether (DME) was studied using ferrierite-based CuZnZr hybrid catalysts. Three different samples were synthesized with different techniques and mass ratios of oxides/zeolite. The activity of the catalysts was found to be higher at higher oxide/zeolite weight ratios. Catalysts prepared by impregnation and coprecipitation showed comparable DME productivity at lower mass ratios, while the physically mixed sample exhibited high CO2 hydrogenation activity but low selectivity towards methanol and DME. Durability tests revealed a progressive loss in activity over time.