Mediating trade-off between activity and selectivity in alkynes semi-hydrogenation via a hydrophilic polar layer.

As a crucial industrial process for the production of bulk and fine chemicals, semi-hydrogenation of alkynes faces the trade-off between activity and selectivity due to undesirable over-hydrogenation. By breaking the energy linear scaling relationships, we report an efficient additive-free WO3-based single-atom Pd catalytic system with a vertical size effect of hydrogen spillover. Hydrogen spillover induced hydrophilic polar layer (HPL) with limited thickness on WO3-based support exhibits unconventional size effect to Pd site, in which over-hydrogenation is greatly suppressed on Pd1 site due to the polar repulsive interaction between HPL and nonpolar C=C bonds, whereas this is invalid for Pd nanoparticles with higher altitudes. By further enhancing the HPL through Mo doping, activated Pd1/MoWO3 achieves recorded performance of 98.4% selectivity and 10200 h-1 activity for semi-hydrogenation of 2-methyl-3-butyn-2-ol, 26-fold increase in activity of Lindlar catalyst. This observed vertical size effect of hydrogen spillover offers broad potential in catalytic performance regulation.

Tailoring a local acid-like microenvironment for efficient neutral hydrogen evolution.

Electrochemical hydrogen evolution reaction in neutral media is listed as the most difficult challenges of energy catalysis due to the sluggish kinetics. Herein, the Ir-HxWO3 catalyst is readily synthesized and exhibits enhanced performance for neutral hydrogen evolution reaction. HxWO3 support is functioned as proton sponge to create a local acid-like microenvironment around Ir metal sites by spontaneous injection of protons to WO3, as evidenced by spectroscopy and electrochemical analysis. Rationalize revitalized lattice-hydrogen species located in the interface are coupled with Had atoms on metallic Ir surfaces via thermodynamically favorable Volmer-Tafel steps, and thereby a fast kinetics. Elaborated Ir-HxWO3 demonstrates acid-like activity with a low overpotential of 20 mV at 10 mA cm-2 and low Tafel slope of 28 mV dec-1, which are even comparable to those in acidic environment. The concept exemplified in this work offer the possibilities for tailoring local reaction microenvironment to regulate catalytic activity and pathway.

Oxygen Vacancy Promoted O2 Activation over Mesoporous Ni-Co Mixed Oxides for Aromatic Hydrocarbon Oxidation.

Whether the oxygen vacancies of heterogeneous catalysts improve their catalytic activity or not has recently been the topic of intense debate in the oxidation of hydrocarbons. We designed an effective strategy to construct mesoporous Ni-Co mixed oxides via a ligand-assisted self-assembly approach. The surface oxygen vacancy concentrations of the mesoporous Ni-Co mixed oxide catalysts were regulated by changing the doping amount of Ni or the reduction method, and the relationship between oxygen vacancies and catalytic activity was studied. Controlled experiments and DFT calculations revealed that oxygen molecules were more favorably adsorbed and activated on oxygen vacancies to form active oxygen species. Increasing the oxygen vacancy concentration within a certain range can effectively enrich the active oxygen species, therefore improving the oxidation rate of ethylbenzene. The optimized mCo3O4-0.1NiO catalyst exhibited a remarkable catalytic activity for the solvent-free oxidation of ethylbenzene to acetophenone, typically including 68.0% conversion and 95.4% selectivity (20 mg mCo3O4-0.1NiO, 10 mL ethylbenzene, and 0.6 MPa O2).

Strong Oxide-Support Interaction over IrO2 /V2 O5 for Efficient pH-Universal Water Splitting.

Constructing strong oxide-support interaction (SOSI) is compelling for modulating the atomic configurations and electronic structures of supported catalysts. Herein, ultrafine iridium oxide nanoclusters (≈1 nm) are anchored on vanadium oxide support (IrO2 /V2 O5 ) via SOSI. The as made catalyst, with a unique distorted IrO2 structure, is discovered to significantly boost the performance for pH-universal oxygen evolution reaction (OER). Based on experimental results and theoretical calculations, the distorted IrO2 active sites with flexible redox states in IrO2 /V2 O5 server as electrophilic centers balance the adsorption of oxo-intermediates and effectively facilitate the process of OO coupling, eventually propelling the fast turnover of water oxidation. As a result, IrO2 /V2 O5 demonstrates not only ultralow overpotentials at 10 mA cm-2 (266 mV, pH = 0; 329 mV, pH = 7; 283 mV, pH = 14) for OER, but also high-performance overall water electrolysis over a broad pH range, with a potential of mere 1.50 V (pH = 0), 1.65 V (pH = 7) or 1.49 V (pH = 14) at 10 mA cm-2 . In addition, SOSI can simultaneously secure the distorted active sites and thus remarkably improving the catalytic stability, making it a promising strategy to develop high-performance catalytic systems.

Porous N-Doped Carbon-Encapsulated CoNi Alloy Nanoparticles Derived from MOFs as Efficient Bifunctional Oxygen Electrocatalysts.

A porous N-doped carbon-encapsulated CoNi alloy nanoparticle composite (CoNi@N-C) was prepared using a bimetallic metal-organic framework composite as the precursor. The optimal prepared Co1Ni1@N-C material at 800 °C exhibited well-defined porosities, uniform CoNi alloy nanoparticle dispersion, a high doped-N level, and scattered CoNi-N x active sites, therefore affording excellent oxygen catalytic activities toward the reduction and evolution processes of oxygen. The oxygen reduction (ORR) onset potential ( Eonset) on Co1Ni1@N-C was 0.91 V and the half-wave potential ( E1/2) was 0.82 V, very close to the parameters recorded on the Pt/C (20 wt Pt%) benchmark. Moreover, it is worth noting that the ORR stability of Co1Ni1@N-C was prominently higher than that of Pt/C. Under the oxygen evolution reaction condition, Co1Ni1@N-C generated the maximum current density at the potential of 1.7 V (8.60 mA cm-2) and the earliest Eonset (1.35 V) among all Co xNi y@N-C hybrids. The Co1Ni1@N-C catalyst exhibited the smallest Δ E value, confirming the superior bifunctional activity. The high surface area and porosity, and CoNi-N x active sites on the carbon surface including the proper interactions between the N-doped C shell and CoNi nanoparticles were attributed as the main contributors to the outstanding oxygen electrocatalytic property and good stability.