Nanostructured copper, chromium, and tin oxide multicomponent materials as catalysts for methanol decomposition: 11C-radiolabeling study

Copper and chromium modified tin oxide nanocomposites were obtained via incipient wetness impregnation of high surface area nanosized SnO2 with the corresponding metal acetylacetonates and their further decomposition in air. Powder X-ray diffraction (XRD), Nitrogen physisorption, UV–Vis, and Temperature-programmed reduction (TPR) with hydrogen were applied for the samples characterization. The catalytic activity of the obtained materials was tested in methanol conversion. A new approach based on the selective coverage of the surface with 11C-methanol was used for the characterization of the catalytic sites. It was demonstrated that the products distribution could be controlled by the surface coverage with methanol and the role of different active sites was discussed. The modification of SnO2 with copper oxide increased the activity in methanol decomposition to CO2via dioxymethylene intermediates, but the catalyst suffered considerable loss of activity due to the reduction transformations by the reaction medium and formation of an inactive intermetallic alloy. The modification with chromium changed the acid-basic properties of SnO2 by the formation of Cr2O3 nanoparticles as well as anchored to the support chromate species. The former particles facilitated the formation of dimethyl ether (DME), while the latter species converted methanol predominantly to hydrocarbons. The fraction of chromate species increased in Cu–Cr–Sn oxide multicomponent nanocomposites and promoted the formation of hydrocarbons over DME at low temperatures, while at higher temperatures, the activity of the copper species leading to CO2 formation was more pronounced.

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► SnO2 promoted the deposition of highly dispersed Cu and Cr oxide particles.
► The close contact between CuO and SnO2 facilitated their reduction.
► CuO species leaded to the formation of strong redox sites onto the SnO2 matrix.
► Cr2O3 nanoparticles insured the formation of Lewis acidic sites.
► The deposition of both oxides facilitated the formation of surface chromate species.