Synthesis RhAg bimetallic composite nanoparticles for improved catalysts on direct synthesis of hydrogen peroxide generation

Atomically precise rhodium-indium carbonyl nanoclusters: synthesis, characterization, crystal structure and electron-sponge features

In this paper we present the investigation of the reactivity of [Rh7(CO)16]3- with InCl3, with the aim of expanding the more general study that allowed us to obtain, among other species, the icosahedral [Rh12E(CO)27]n- (n = 4 when E = Ge or Sn; n = 3 when E = Sb or Bi) family of clusters. Indeed, the study resulted in the isolation and characterization of the analogous In-centred icosahedral [Rh12In(CO)28]3- nanocluster (1), which is isoelectronic and isostructural with the [Rh12E(CO)27]n- congeners. During the course of the reaction two more new species, namely the octahedral [Rh6(CO)15InCl3]2- (2) and the dimeric [{Rh6(CO)15InCl2}2]2- (3) have also been identified. The reaction between [Rh7(CO)16]3- and InCl3 proved to be poorly selective; nevertheless, by fine tuning some reaction parameters it was possible to drive the reaction more towards one product or the other. Alternatively, [Rh6(CO)15InCl3]2- can be more selectively prepared by reacting either [Rh5(CO)15]- or, less efficiently, [Rh6(CO)15]2- with InCl3. As for the dimeric [{Rh6(CO)15InCl2}2]2- species, this was only isolated by carrying out the reaction with [Rh7(CO)16]3- under inert atmosphere, as opposed to under CO. All clusters were characterized by IR spectroscopy and ESI-MS, and their molecular structures were fully established by single-crystal X-ray diffraction studies. The [Rh12In(CO)28]3- species was also analysed by EDS via SEM, and further investigated through in situ infrared spectroelectrochemistry and CV experiments to check its multivalence nature. Indeed, [Rh12In(CO)28]3- can reversibly undergo two monoelectronic oxidation and one bi-electronic reduction processes, behaving like an electron sponge and, thus, giving rise to the further [Rh12In(CO)28]n- derivatives (n = 1, 2 and 5). These results parallel the findings for the [Rh12E(CO)27]n- series. The geometry variations of the metal framework associated with the changes in the cluster negative charge were investigated by means of DFT calculations.

Facile Direct Seed-Mediated Growth of AuPt Bimetallic Shell on the Surface of Pd Nanocubes and Application for Direct H2O2 Synthesis

The selective enhancement of catalytic activity is a challenging task, as catalyst modification is generally accompanied by both desirable and undesirable properties. For example, in the case of the direct synthesis of hydrogen peroxide, Pt on Pd improves hydrogen conversion, but lowers hydrogen peroxide selectivity, whereas Au on Pd enhances hydrogen peroxide selectivity but decreases hydrogen conversion. Toward an ideal catalytic property, the development of a catalyst that is capable of improving H-H dissociation for increasing H2 conversion, whilst suppressing O-O dissociation for high H2O2 selectivity would be highly beneficial. Pd-core AuPt-bimetallic shell nanoparticles with a nano-sized bimetallic layer composed of Au-rich or Pt-rich content with Pd cubes were readily prepared via the direct seed-mediated growth method. In the Pd-core AuPt-bimetallic shell nanoparticles, Au was predominantly located on the {100} facets of the Pd nanocubes, whereas Pt was deposited on the corners of the Pd nanocubes. The evaluation of Pd-core AuPt-bimetallic shell nanoparticles with varying Au and Pt contents revealed that Pd-core AuPt-bimetallic shell that was composed of 2.5 mol% Au and 5 mol% Pt, in relation to Pd, exhibited the highest H2O2 production rate (914 mmol H2O2 gmetal−1 h−1), due to the improvement of both H2O2 selectivity and H2 conversion.

Effect of polyvinylpyrrolidone (PVP) on palladium catalysts for direct synthesis of hydrogen peroxide from hydrogen and oxygen

Addition of polyvinylpyrrolidone to Pd/SiO₂ catalyst improved H₂O₂ selectivity by adjusting electronic state of palladium active species.