Comparative study of hydrotalcite-derived supported Pd₂Ga and PdZn intermetallic nanoparticles as methanol synthesis and methanol steam reforming catalysts

An effective and versatile synthetic approach to produce well-dispersed supported intermetallic nanoparticles is presented that allows a comparative study of the catalytic properties of different intermetallic phases while minimizing the influence of differences in preparation history. Supported PdZn, Pd2Ga, and Pd catalysts were synthesized by reductive decomposition of ternary Hydrotalcite-like compounds obtained by co-precipitation from aqueous solutions. The precursors and resulting catalysts were characterized by HRTEM, XRD, XAS, and CO-IR spectroscopy. The Pd2+ cations were found to be at least partially incorporated into the cationic slabs of the precursor. Full incorporation was confirmed for the PdZnAl-Hydrotalcite-like precursor. After reduction of Ga- and Zn-containing precursors, the intermetallic compounds Pd2Ga and PdZn were present in the form of nanoparticles with an average diameter of 6 nm or less. Tests of catalytic performance in methanol steam reforming and methanol synthesis from CO2 have shown that the presence of Zn and Ga improves the selectivity to CO2 and methanol, respectively. The catalysts containing intermetallic compounds were 100 and 200 times, respectively, more active for methanol synthesis than the monometallic Pd catalyst. The beneficial effect of Ga in the active phase was found to be more pronounced in methanol synthesis compared with steam reforming of methanol, which is likely related to insufficient stability of the reduced Ga species in the more oxidizing feed of the latter reaction. Although the intermetallic catalysts were in general less active than a Cu-/ZnO-based material prepared by a similar procedure, the marked changes in Pd reactivity upon formation of intermetallic compounds and to study the tunability of Pd-based catalysts for different reactions

Photocatalytic hydrogen production from water using N-doped Ba(5)Ta(4)O(15) under solar irradiation

Solar light induced water splitting on photocatalysts is a very important area of research. Anion doping of photocatalysts normally active only under ultraviolet (UV) light has been reported to be a possible way of increasing visible light photocatalytic performance. Here we report a (111) layered perovskite material Ba5Ta4O15 that was doped with nitrogen. The resulting Ba5Ta4O15-xNx compound exhibited an extraordinary increase in visible light absorbance. The uniform distribution of the nitrogen dopant was attributed to the unique layered (111) structure, which provides intergallery spacings between the perovskite layers for the dopant to diffuse easily in the compound particles during the doping process. It was further verified by density of states that the N 2p states mixed with pre-existing 0 2,p states that moved the valence band maximum upward without effecting the conduction band, which was composed of the Ta 4d orbital. The doped photocatalysts exhibited not only increased visible light absorbance but increased photocatalytic hydrogen production of similar to 50% under simulated solar irradiation, in comparison to that of undoped parent compound

Nitrogen doped Sr(2)Ta(2)O(7) coupled with graphene sheets as photocatalysts for increased photocatalytic hydrogen production

In this work we present the synthesis of a new type of nitrogen-doped tantalate, Sr2Ta2O7-xNx, which exhibited significantly Increased visible light absorption and improved photocatalytic hydrogen production by 87% under solar irradiation, compared with its undoped counterpart Sr2Ta2O7. The photocatalyst also exhibited a strong capability in photoinduced reduction of exfoliated graphene oxide (GO) to graphene sheets. By using graphene as a support for a Pt cocatalyst, a new type of composite containing graphene-Pt and Sr2Ta2O7-xNx was designed, which demonstrated an additional similar to 80% increase In hydrogen production and an quantum efficiency of 6.45% (similar to 177% increase from pristine undoped Sr2Ta2O7) due to the efficient charge carrier separation on the photocatalyst. This work suggests that graphene can play an important role as an electron transfer highway, which facilitates the charge carrier collection onto Pt cocatalysts. The method can thus be considered as an excellent strategy to increase photocatalytic hydrogen production in addition to a commonly applied doping method