Green Synthesis of Highly Dispersed Ni/SiO2 Catalysts Using Natural Biomass of Sesbania Powder

Important role of H2 spillover in asymmetric hydrogenation of quinolines in hybrid systems

The phenomenon of hydrogen spillover usually involved in the hydrogenation reactions over supported metal catalysts has been seldom reported over molecular catalysts. Herein, we report the important role of hydrogen spillover in homogeneous hydrogenation with the asymmetric hydrogenation of quinolines as a model reaction. It is observed that the conversion of quinaldine over TsDPEN-Rh-Cp*-Cl catalyst is sharply increased by 2.1 folds in the presence of Ni/TiO2 and the ee value remained at the same level. The mechanism study shows that Ni/TiO2 is mainly used as H2 dissociation site, TsDPEN-Rh-Cp*-Cl is the active site to control the enantioselectivity of the product, and hydrogen spillover acts as a bridge between the two catalysts in the homogeneous and heterogeneous hybrid system. The hydrogen spillover makes it possible for heterogeneous catalysts and homogeneous organometallic complexes to cooperate, breaking the boundary between homogeneous and heterogeneous catalysis.

Construction of Ni/In2O3 Integrated Nanocatalysts Based on MIL-68(In) Precursors for Efficient CO2 Hydrogenation to Methanol

The efficient and economic conversion of CO2 and renewable H2 into methanol has received intensive attention due to growing concern for anthropogenic CO2 emissions, particularly from fossil fuel combustion. Herein, we have developed a novel method for preparing Ni/In2O3 nanocatalysts by using porous MIL-68(In) and nickel(II) acetylacetonate (Ni(acac)2) as the dual precursors of In2O3 and Ni components, respectively. Combined with in-depth characterization analysis, it was revealed that the utilization of MIL-68(In) as precursors favored the good distribution of Ni nanoparticles (∼6.2 nm) on the porous In2O3 support and inhibited the metal sintering at high temperatures. The varied catalyst fabrication parameters were explored, indicating that the designed Ni/In2O3 catalyst (Ni content of 5 wt %) exhibited better catalytic performance than the compared catalyst prepared using In(OH)3 as a precursor of In2O3. The obtained Ni/In2O3 catalyst also showed excellent durability in long-term tests (120 h). However, a high Ni loading (31 wt %) would result in the formation of the Ni-In alloy phase during the CO2 hydrogenation which favored CO formation with selectivity as high as 69%. This phenomenon is more obvious if Ni and In2O3 had a strong interaction, depending on the catalyst fabrication methods. In addition, with the aid of in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory (DFT) calculations, the Ni/In2O3 catalyst predominantly follows the formate pathway in the CO2 hydrogenation to methanol, with HCOO* and *H3CO as the major intermediates, while the small size of Ni particles is beneficial to the formation of formate species based on DFT calculation. This study suggests that the Ni/In2O3 nanocatalyst fabricated using metal-organic frameworks as precursors can effectively promote CO2 thermal hydrogenation to methanol.

Enzyme-Compatible Core-Shell Nanoreactor for in Situ H2 -Driven NAD(P)H Regeneration

The regeneration of the reduced form cofactor NAD(P)H is essential for the extra-cellular application of bio-reduction, which necessitates not only the development of efficient artificial NAD(P)H regeneration catalytic system but also its well compatibility with the cascade enzymatic reduction system. In this work, we reported the preparation of a metal nanoparticle (NP) and metal complex integrated core-shell nanoreactor for H2 -driven NAD(P)H regeneration through the immobilization of a Rh complex on Ni/TiO2 surface via a bipyridine contained 3D porous organic polymer (POP). In comparison with the corresponding single component metal NPs and the immobilized Rh complex, the integrated catalyst presented simultaneously enhanced activity and selectivity in NAD(P)H regeneration thanks to the rapid spillover of activated H species from metal NPs to Rh complex. In addition, the size-sieving effect of POP precluded the direct interaction of enzyme and Rh complex confined in the pores, enabling the success coupling of core-shell nanoreactor and aldehyde ketone reductase (AKR) for chemoenzymatic reduction of acetophenone to (R)-1-phenylethan-1-ol. This work provides a strategy for the rational manipulation of multicomponent cooperation catalysis.

Synthesis of Mesoporous Silica-Supported NiCo Bimetallic Nanocatalysts and Their Enhanced Catalytic Hydrogenation Performance

In this work, mesoporous silica SBA-16-supported NiCo bimetallic nanocatalysts were synthesized by coimpregnation of Ni and Co precursors followed by calcination and reduction, and various characterization techniques confirm the formation of NiCo bimetallic nanostructures in the catalysts. The synthesized NiCo/SBA-16 shows enhanced catalytic performance for hydrogenation of a series of nitroaromatics. Under the reaction conditions of 80 °C and 1.0 MPa of H₂, the yields of aniline for nitrobenzene hydrogenation over NiCo_0.3/SBA-16 can reach more than 99% at 2.0 h. The enhanced catalytic performance can be ascribed to the formation of NiCo bimetallic nanostructures, where the synergistic effect between Ni and Co improves their catalytic activities for hydrogenation of nitroaromatics.

Antioxidants: Classification, Natural Sources, Activity/Capacity Measurements, and Usefulness for the Synthesis of Nanoparticles

Natural extracts are the source of many antioxidant substances. They have proven useful not only as supplements preventing diseases caused by oxidative stress and food additives preventing oxidation but also as system components for the production of metallic nanoparticles by the so-called green synthesis. This is important given the drastically increased demand for nanomaterials in biomedical fields. The source of ecological technology for producing nanoparticles can be plants or microorganisms (yeast, algae, cyanobacteria, fungi, and bacteria). This review presents recently published research on the green synthesis of nanoparticles. The conditions of biosynthesis and possible mechanisms of nanoparticle formation with the participation of bacteria are presented. The potential of natural extracts for biogenic synthesis depends on the content of reducing substances. The assessment of the antioxidant activity of extracts as multicomponent mixtures is still a challenge for analytical chemistry. There is still no universal test for measuring total antioxidant capacity (TAC). There are many in vitro chemical tests that quantify the antioxidant scavenging activity of free radicals and their ability to chelate metals and that reduce free radical damage. This paper presents the classification of antioxidants and non-enzymatic methods of testing antioxidant capacity in vitro, with particular emphasis on methods based on nanoparticles. Examples of recent studies on the antioxidant activity of natural extracts obtained from different species such as plants, fungi, bacteria, algae, lichens, actinomycetes were collected, giving evaluation methods, reference antioxidants, and details on the preparation of extracts.