The direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 represents a potentially atom-efficient alternative to the current industrial indirect process. We show that the addition of tin to palladium catalysts coupled with an appropriate heat treatment cycle switches off the sequential hydrogenation and decomposition reactions, enabling selectivities of >95% toward H2O2. This effect arises from a tin oxide surface layer that encapsulates small Pd-richparticles while leaving larger Pd-Sn alloy particles exposed. We show that this effect is a general feature for oxide-supported Pd catalysts containing an appropriate second metal oxide component, and we set out the design principles for producing high-selectivity Pd-based catalysts for direct H2O2 production that do not contain gold.
Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored—georgeite. The first three of theseminerals are widely used as catalyst precursors for the industrially important methanol-synthesis and low-temperature water–gas shift (LTS) reactions, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite;with few exceptions it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that super critical antisolvent (SAS) precipitation using carbon dioxide, a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts.
3. 按惯例分享J. Catal.一篇，关注点: Catalyst–soot contact points, surface oxygen vacancies.
Three model ceria catalysts, which are monocrystalline CeO2 nanocubes, polycrystalline CeO2 nanoparticles, and polycrystalline CeO2 spindles, were synthesized and analyzed with isothermal soot oxidation, H2-TPR, and Raman spectroscopy. The results suggest that the initial activity of the catalyst is determined by the number of catalyst–soot contact points rather than the catalyst surface area, while the catalyst stability is closely related to the concentration of surface oxygen vacancies. Excessive surface oxygen vacancies may inhibit the regeneration of highly active O2− and lead to catalyst deactivation during reaction. After impregnation with Ag, O− can be readily regenerated and transformed to O2−, resulting in a10-fold increase in soot oxidation activity over Ag/CeO2. Among these catalysts, Ag supported on nanocubic CeO2 exhibits good availability of O2− and therefore high catalytic activityand stability, and is thus considered a promising catalyst for application in gasoline particulate filters.