Selective Hydrogenation Properties of Ni-Based Bimetallic Catalysts

Metallic Ni shows high activity for a variety of hydrogenation reactions due to its intrinsically high capability for H2 activation, but it suffers from low chemoselectivity for target products when two or more reactive functional groups are present on one molecule. Modification by other metals changes the geometric and electronic structures of the monometallic Ni catalyst, providing an opportunity to design Ni-based bimetallic catalysts with improved activity, chemoselectivity, and durability. In this review, the hydrogenation properties of these catalysts are described starting from the typical methods of preparing Ni-based bimetallic nanoparticles. In most cases, the reasons for the enhanced catalysis are discussed based on the geometric and electronic effects. This review provides new insights into the development of more efficient and well-structured non-noble metal-based bimetallic catalytic systems for chemoselective hydrogenation reactions.

Investigation of Ni catalyst activation during plasma-assisted methane oxidation

Atmospheric pressure plasma has shown promise in improving thermally activated catalytic reactions through a process termed plasma-catalysis synergy. In this work, we investigated atmospheric pressure plasma jet (APPJ)-assisted CH4 oxidation over a Ni/SiO2.Al2O3 catalyst. Downstream gas-phase products from CH4 conversion were quantified by Fourier transform infrared spectroscopy (FTIR). The catalyst near-surface region was characterized by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalyst was observed to be activated at elevated temperature (500 °C) if it was exposed to the APPJ operated at large plasma power. “Catalyst activation” signifies that the purely thermal conversion of CH4 using catalysts which had been pre-exposed to plasma became more intense and produced consistently CO product, even if the plasma was extinguished. Without the application of the APPJ to the Ni catalyst surface this was not observed at 500 °C. The study of different exposure conditions of the activated catalyst indicates that the reduction of the catalyst by the APPJ is likely the cause of the catalyst activation. We also observed a systematic shift of the vibrational frequency of adsorbed CO on Ni catalyst when plasma operating conditions and catalyst temperatures were varied and discussed possible explanations for the observed changes. This work provides insights into the plasma-catalyst interaction, especially catalyst modification in the plasma catalysis process, and potentially demonstrates the possibility of utilizing the surface CO as a local probe to understand the plasma-catalyst interaction and shed light on the complexity of plasma catalysis.

Photosensitized Nickel Catalysis Enabled Silyl Radical Mediated Direct Activation of Carbamoyl Chlorides to Access (Hetero)aryl Carbamides

The transformation of a readily available molecule to a medicinally relevant functionality is the heart of organic synthesis which literally unfolds new direction in the field of drug discovery and development. Accordingly, synthetic chemistry fraternity is constantly striving to introduce a range of avant-garde techniques to construct an incredibly important fundamental entity like “amide bonds” which connect the amino acids in proteins and exist as a prevalent structural motif in biomolecules. In this context, we want to introduce the concept of cross-electrophile coupling by merging the photoredox and transition metal catalysis to construct carbamides from superabundant (hetero)aryl chlorides or bromides along with commercially feasible carbamoyl chlorides. However, there is barely any report on direct activation of carbamoyl chloride so far. To circumvent the challenge, we employ the intrinsic affinity of silyl radical species towards halogen atom to harness the carbamoyl radical directly from carbamoyl chlorides which is seemingly the first of its kind. The success of this protocol relies on the prior formation of ‘aryl halides to Ni-catalyst’ oxidative addition intermediate that assists in generation of the vital carbamoyl radical. The breadth of application of this technique is significantly demonstrated by the synthesis of a plethora of (hetero)aryl carbamides with diverse functionalities. As stated earlier, we outline the direct utility of this protocol by the late-stage amidation of halide containing drug molecules and pharmacophores.

CO2 Reforming of CH4 Using Coke Oven Gas over Ni/MgO-Al2O3 Catalysts: Effect of the MgO:Al2O3 Ratio

Research is being actively conducted to improve the carbon deposition and sintering resistance of Ni-based catalysts. Among them, the Al2O3-supported Ni catalyst has been broadly studied for the dry reforming reaction due to its high CH4 activity at the beginning of the reaction. However, there is a problem of deactivation due to carbon deposition of Ni/Al2O3 catalyst and sintering of Ni, which is a catalytically active material. Supplementing MgO in Ni/Al2O3 catalyst can result in an improved MgAl2O4 spinel structure and basicity, which can be helpful for the activation of methane and carbon dioxide molecules. In order to confirm the optimal supports’ ratio in Ni/MgO-Al2O3 catalysts, the catalysts were prepared by supporting Ni after controlling the MgO:Al2O3 ratio stepwise, and the prepared catalysts were used for CO2 reforming of CH4 (CDR) using coke oven gas (COG). The catalytic reaction was conducted at 800 °C and at a high gas hourly space velocity (GHSV = 1,500,000 h−1) to screen the catalytic performance. The Ni/MgO-Al2O3 (MgO:Al2O3 = 3:7) catalyst showed the best catalytic performance between prepared catalysts. From this study, the ratio of MgO:Al2O3 was confirmed to affect not only the basicity of the catalyst but also the dispersion of the catalyst and the reducing property of the catalyst surface.

The Ni Catalyst Supported on the FSP-made Transition Metal (Co, Mn, Cu or Zn) Doped La2O3 Material for the Dry Reforming of Methane

The transition metal (Co, Mn, Cu or Zn) doped La2O3 material was prepared by flame spray pyrolysis (FSP) technique. The 2 wt.% Ni catalyst supported on this material was characterized by XRD, N2 physisorption, TPR, H2 chemisorption and TGA, and evaluated by the dry reforming of methane (DRM). The perovskite structure was certainly formed when either Co or Mn was introduced. The Cu can generate the La2CuO4 spinel phase while the Zn showed a mixed phase of La2O3, ZnO and La(OH)3. The Ni/Co-La2O3 catalyst was more active for the DRM because of high amount of active dual sites of Ni and Co metals dispersed on the catalyst surface. The formation of La2O2CO3 during the reaction can inhibit the coke formation. The cooperation of La2O2CO3 and MnO phases in the Ni/Mn-La2O3 catalyst was promotional effect to decrease carbon deposits on the catalyst surface. The partial substitution of Co for Mn with a small content of Mn can enhance the catalytic activity and the product yield. The Ni/Mn0.05Co0.95-La2O3 catalyst showed the highest CH4 conversion, H2 yield and H2/CO ratio. The Mn inserted into the perovskite structure of LaCoO3 was an important player to change oxygen mobility within the crystal lattice to maintain a high performance of the catalyst. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).