Controlled deposition of titanium oxide overcoats by non-hydrolytic sol gel for improved catalyst selectivity and stability

Advances in the synthetic control of surface nanostructures could improve the activity, selectivity and stability of heterogeneous catalysts. Here, we present a technique for the controlled deposition of TiO2 overcoats based on non-hydrolytic sol-gel chemistry. Continuous injection of Ti(iPrO)4 and TiCl4 mixtures led to the formation of conformal TiO2 overcoats with a growth rate of 0.4 nm/injected monolayer on several materials including high surface area SBA-15. Deposition of TiO2 on SBA-15 generated medium-strength Lewis acid sites, which catalyzed 1-phenylethanol dehydration at high selectivities and decreased deactivation rates compared to typically used HZSM-5. When supported metal nanoparticles were similarly overcoated, the intimate contact between the metal and acid sites at the support-overcoat interface significantly increased propylcyclohexane selectivity during the deoxygenation of lignin-derived propyl guaiacol (89% at 90% conversion compared to 30% for the uncoated catalyst). For both materials, the surface reactivity could be tuned with the overcoat thickness

Enhanced Oxygen Reduction Reaction on Fe/N/C Catalyst in Acetate Buffer Electrolyte

Non-precious metal catalysts (NPMCs) have gained significant attention over the past decade as realistic alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR) in fuel cells. An interesting feature of NPMCs is that the active site can be regarded as a 2D structure where both sides influence the catalytic process. Such a 2D structure enables different possibilities to alter the active site through the specific chemical environment as compared with typical 3D materials such as Pt based catalysts. In this work, we focus on the effect of carboxylate buffer species in the vicinity of iron–nitrogen-carbon (Fe/N/C) catalytic sites. The catalytic interface is studied with respect to the ORR activity using the rotating disk electrode (RDE) in aqueous electrolyte as well as theoretical modeling using density functional theory (DFT) calculations. We find that the ORR activity on Fe/N/C catalyst is promoted by carboxyl species in general and increases 4-fold in acetate buffer as compared to 0.1 M aqueous HClO4 electrolyte

Activity-Selectivity Trends in the Electrochemical Production of Hydrogen Peroxide over Single-Site Metal-Nitrogen-Carbon Catalysts

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P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction

This contribution reports the discovery and analysis of a p-block Sn-based catalyst for the electroreduction of molecular oxygen in acidic conditions at fuel cell cathodes; the catalyst is free of platinum-group metals and contains single-metal-atom actives sites coordinated by nitrogen. The prepared SnNC catalysts meet and exceed state-of-the-art FeNC catalysts in terms of intrinsic catalytic turn-over frequency and hydrogen–air fuel cell power density. The SnNC-NH3 catalysts displayed a 40–50% higher current density than FeNC-NH3 at cell voltages below 0.7 V. Additional benefits include a highly favourable selectivity for the four-electron reduction pathway and a Fenton-inactive character of Sn. A range of analytical techniques combined with density functional theory calculations indicate that stannic Sn(iv)Nx single-metal sites with moderate oxygen chemisorption properties and low pyridinic N coordination numbers act as catalytically active moieties. The superior proton-exchange membrane fuel cell performance of SnNC cathode catalysts under realistic, hydrogen–air fuel cell conditions, particularly after NH3 activation treatment, makes them a promising alternative to today’s state-of-the-art Fe-based catalysts