Nickel and iridium supported on SiO2 (Ni–Ir/SiO2) acted as an effective and reusable heterogeneous catalyst for hydrogenation of olefins, and it showed higher activity and selectivity than the monometallic counterparts.

Metal-alloyed atomic catalysts such as single-atom alloys have attracted much attention due to their high atom economy and their unique catalytic properties. Recently, we found that a SiO2-supported Ni-Ir alloy (Ni-Ir/SiO2) was an effective heterogeneous catalyst for the hydrogenation of styrene and that the isolated Ni atom surrounded by Ir metal atoms, an Ir-alloyed Ni single atom, in the Ni-Ir alloy was the main active site, showing much higher activity in comparison with the monometallic Ir/SiO2 and Ni/SiO2. Reports on such effective metal-alloyed non-noble-metal single-atom catalysts are limited, and their catalytic potential should be clarified. In this study, bimetallic catalysts composed of non-noble metals and noble metals were comprehensively scrutinized in the hydrogenation of styrene as a model reaction. Among various combinations, Ni-Ir/SiO2 (introduced Ni/Ir molar ratio 1) showed the largest rate enhancement (7-fold) in comparison with the monometallic counterpart catalysts, while a SiO2-supported Co-Ir alloy (Co-Ir/SiO2, introduced Co/Ir molar ratio 4) and Ni-Pt alloy (Ni-Pt/SiO2, introduced Ni/Pt molar ratio 0.25) were also effective. The activity orders were Co-Ir/SiO2 > Ir/SiO2 > Co/SiO2 and Ni-Pt/SiO2 > Pt/SiO2 > Ni/SiO2, and the (Co-Ir/SiO2)/(Ir/SiO2) and (Ni-Pt/SiO2)/(Pt/SiO2) activity ratios were 3.5 and 2.5, respectively. Moreover, Ni-Ir/SiO2 showed higher activity for the hydrogenation of various olefins in comparison to the monometallic Ir/SiO2 and Ni/SiO2. The reaction mechanism of styrene hydrogenation over the Ir-alloyed Ni single atom of Ni-Ir/SiO2 was proposed on the basis of spectroscopic studies such as FTIR, XPS, and XRD, kinetic studies such as the effect of substrate concentration and H2 pressure, the isotopic effect of hydrogen, and the effect of the reaction temperature, and DFT calculations. The rate-determining step is the second hydrogenation of the half-hydrogenated styrene adspecies on an Ni atom by H species on Ir atoms in the Horiuti–Polanyi mechanism. The single Ni atom in Ir metal atoms has two roles: (1) formation of the reactive half-hydrogenated styrene adspecies on Ni atom and (2) formation of the reactive H species on Ir atoms by the electron transfer from an Ni atom to Ir atoms. These roles resulted in a low activation energy, leading to a large rate enhancement in comparison to the monometallic counterpart catalysts.

S,N-co-doped porous carbon ( SNPC ) materials are good candidates for cathodic oxygen-reduction reaction ( ORR ) and lithium-ion batteries ( LIBs ). However, SNPC has low yield and high cost. Herein, we reported a new and efficient method of synthesizing S,N-co-doped mesoporous carbon material through the carbonization of S,N-containing precursors in molten ZnCl2, where ZnCl2 served as the ionic solvent and Lewis catalyst. The resultant SNPC-800 showed a mesoporous structure with a specific surface area of 1235 m²/g and mesopore-size range of 10-45 nm, which was considerably larger than those obtained through carbonization of ionic-liquid and fabrication of graphene oxides. Furthermore, ORR measurements exhibit good catalytic activity, comparable to the commercial Pt/C catalyst. Also the SNPC-800 material exhibited excellent good catalytic stability, and a high methanol tolerance compared to the commercial Pt/C catalyst. Density functional theory calculation results revealed that the catalytic property originated from the synergistic effect of S/N dopant and that the main catalytic reaction path followed an associative mechanism. LIB tests further showed high reversible capacity, as well as excellent cycling stability and rate performance.