The application of electrochemical CO2 reduction reaction (CO2RR) to generate value-added products, including carbon monoxide (CO), represents a sustainable strategy for addressing the global carbon balance. Silver (Ag) has gained significant attention as an attractive and cost-effective electrocatalyst for CO2RR-to-CO due to high activity.  Here, the porous Ag nanofoam catalysts with Ag(111)-dominant were prepared by in-situ electrolysis-deposition method in the ionic liquid (IL) electrolyte. The Ag nanofoam catalysts exhibited exceptional activity in converting CO2 to CO, with a high Faradaic efficiency (> 95%) in a wide range of -1.9 ~ -2.4 V vs. Ag/Ag+ in the 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) electrolyte. The maximum CO partial current density of -125.40 mA cm-2 was obtained on this Ag nanofoam catalyst, representing 62% improvement over Ag(110)-dominant Ag electrode (-77.35 mA cm-2) at -2.4 V vs Ag/Ag+ in the [Bmim][BF4] electrolyte. Density functional theory calculations demonstrate that the Ag(111) crystal facet formed by in-situ electrolysis-deposition method prefers to adsorb [Bmim][BF4] which can stabilize the reaction intermediate, thereby weakening the reaction free energy and promoting CO2 electroreduction.

Ruthenium nanoparticles stabilised by an amine-modified Ordered Mesoporous Silica Immobilized Ionic Liquid (OMSIIL) are efficient catalysts for the partial reduction of nitrobenzene to hydrazobenzene with 100% selectivity as well as the complete reduction to aniline. High selectivity for the partial reduction of nitrobenzene to hydrazobenzene was obtained when the reaction was conducted in ethanol with 0.5 mol% catalyst and NaBH4 as the hydrogen donor whereas aniline was obtained as the sole product in water when dimethylamine borane (DMAB) was used as the hydrogen donor. Interestingly, while a range of electron poor nitroarenes were reduced to the corresponding hydrazoarene with high selectivities and good conversions, nitroarenes substituted with electron donating groups resulted in complete reduction to the aniline. Composition-time profiles suggest that reductions conducted in ethanol with sodium borohydride occur via the condensation pathway while those conducted in water using dimethylamine borane as the hydrogen source may well go via the direct pathway. This is the first example of the selective reduction of nitrobenzene to hydrazobenzene using a ruthenium nanoparticle-based catalyst and the initial TOF of 320 mol nitrobenzene converted mol Ru-1 h-1 is markedly higher than previous literature reports.

Direct asymmetric hydrogenation (AH) and asymmetric transfer hydrogenation (ATH) reactions are among the most efficient approaches to produce chiral building blocks. Recently, these types of transformations have witnessed a shift towards the use of molecular catalysts based on earth-abundant transition metals due to their ready availability, economic advantage, and novel properties. With particular regard to manganese, catalyst development has seen both the efficiency and substrate scope in AH and ATH greatly improved, with the emergence of a large number of well-defined Mn-complexes employed in this field. The reaction scope includes the AH and ATH of C=O bonds, asymmetric reduction of C=N bonds and the asymmetric reductive transformations of C=C bonds. Herein, our survey of the area focuses on the catalytic activity of such complexes, their versatility towards asymmetric transformations and the routes employed to convert substrates to their target molecules. We consider the collected findings of this article will be helpful to the reader by providing an insight into ligand design, thereby aiding future catalyst development. Moreover, this review is aimed at highlighting the remarkable progress made in the last six years in the development of manganese complexes for enantioselective reduction.

The selective oxidation of lower olefins over bismuth molybdate based multicomponent catalysts are key reactions in chemical industry for the functionalization of hydrocarbons. To understand the catalysts’ working principles, three Bi−Mo−Co−Fe-oxides were synthesized, tested in the selective oxidation of propylene and isobutene and characterized by complementary Raman spectroscopy, X-ray absorption spectroscopy and synchrotron X-ray diffraction. Comparison of their catalytic behavior in both reactions provided fundamental insights into the corresponding structure-activity correlations.

Abstract

The elucidation of structure-activity correlations in selective oxidation of propylene and isobutene over mixed metal oxides (MMO) is attractive for knowledge-based catalyst design and process optimisation. Particularly, 4-component Bi−Mo−Co−Fe−O catalysts need to be studied since their complex metal oxide phase mixture leads to higher activity and selectivity than 2-component Bi−Mo−O. Hence, three Bi−Mo−Co−Fe-oxides with different metal ratios were prepared by hydrothermal synthesis and compared during selective oxidation tests with propylene and isobutene. The active phases after several days on stream were investigated by synchrotron X-ray diffraction (XRD) and Raman spectroscopy, while the structural evolution under reaction conditions was followed by operando Raman spectroscopy, synchrotron XRD, and multi-edge X-ray absorption spectroscopy. Similar structural transformations were observed during selective oxidation of propylene and isobutene, with similar influence on catalytic performance. A phase mixture of β-CoMoO₄/β-Co_0.7Fe_0.3MoO₄, γ-Bi₂MoO₆, Fe₃O₄ and Bi₃FeMo₂O₁₂ was observed, whereby high amounts of β-CoMoO₄/β-Co_0.7Fe_0.3MoO₄ increased selectivity to acrolein/methacrolein. In contrast, high amounts of γ-Bi₂MoO₆ and Fe₃O₄ favoured total oxidation to CO and CO₂. The simultaneous presence of β-CoMoO₄/β-Co_0.7Fe_0.3MoO₄, Bi₃FeMo₂O₁₂ and Fe₂O₃ increased selectivity to methacrolein in isobutene oxidation, whereas no comparative increase in acrolein selectivity was observed in propylene oxidation. This suggests different key active phases in both reactions.

N-heterocyclic carbene-catalyzed cross-coupling reaction has been recognized as an enabling tool in the synthesis of complex ketones in recent years. This strategy enables the direct acylation of various alkyl halides under an organocatalytic system.

Abstract

During the past decades, N-heterocyclic carbene (NHC)-catalyzed reactions have emerged as a versatile tool in synthetic chemistry. In particular, NHC-catalyzed cross-coupling reaction has been significantly developed in many respects, including new reaction development and mechanistic investigation. This concept article presents recent advances towards direct cross-coupling reactions of aldehydes with alkyl halides enabled by NHC organocatalysis.

As an excellent class of electrode materials, carbon-based materials have garnered sustained attention. Constructing carbon-based skeleton with unique structure has become a vital research area in the fields of electrocatalysis. Recently, surface curvature has been extensive discussed as a compelling factor in electronic modulation for electrocatalyst design. Benefitting from its distinctive regulation, the intrinsic activity and service stability of catalysts during electrocatalytic process can be significantly improved. Therefore, a helical structure that adeptly integrates well-regulated, highly ordered surface curvatures is considered to be of great research value for the synthesis of carbon-based skeleton. In this Concept article, we systematically summarize the up-to-date reports on the synthetic methods of carbon-based skeletons with helical structures and present major challenges in this field. We also emphasize that the helical carbon-based skeleton could be combined with transition metals for cooperative coupling, potentially leading to the further development of high-efficiency electrocatalysts.

This review systematically summarizes and highlights recent developments on the strategy of tailoring the distribution of active species in heterogeneous catalysis, which effectively enhances the controlling of molecular weight distribution, branch distribution, as well as chain entanglements. The application of different spectroscopic methods for assisting the design of heterogeneous catalysts is also introduced.

Abstract

Heterogeneous catalysis is the most widely used process for ethylene polymerization in industry. Active site distribution is one of the crucial issues in the heterogeneous catalysis, which strongly influences the catalytic process and the microstructure of synthesized polyethylene. In this respect, aiming at an explicit understanding of the progress, the challenge and the possible future directions in the study of heterogeneous catalysis of ethylene polymerization, the recent strategies of designing heterogeneous catalysts are reviewed from the perspective of tailoring the active site distribution, where the regulation of chain structures, including molecular weight distribution, branch distribution and entanglement state, are highlighted. The in situ and operando characterizations are also reviewed for assisting the understanding of structural information in heterogeneous catalysts.

A synergetic cocatalytic effect provided by an iodonium salt in the base-catalyzed Knoevenagel condensation has been found. The diphenyliodonium triflate serving as the halogen bond-donating Lewis acid provides the higher cocatalytic effect than zinc(II) triflate or triflic acid serving.

Abstract

The experimentally obtained kinetic data has indicated the existence of a synergetic cocatalytic effect provided by an iodonium salt in the base-catalyzed Knoevenagel condensation. The diphenyliodonium triflate serving as the halogen bond-donating Lewis acid provides the higher cocatalytic effect than zinc(II) triflate or triflic acid serving, respectively, as the metal cation-based Lewis acid and Brønsted acid. Such a cocatalytic effect remains the same for a broad scope of carbonyl compounds covering aldehydes featuring electron-withdrawing or electron-donating substituents, as well as ketone involved in the reaction.

A C3-symmetric amino–based organocatalyst can be easily prepared starting from chiral trans-N-Boc-1,2-diaminocyclohexane. Its activity on asymmetric synthesis of warfarin and analogues has been explored allowing moderate–high yields and good stereoselectivity with very low catalyst loading. Up to three active units work in the catalytic process as confirmed by offline ESI-MS experiments. In addition, DFT calculations supported the plausible reaction mechanism.

Abstract

A novel C3-symmetric multi–amino catalyst was synthesized and evaluated in the asymmetric Michael addition to produce warfarin and its analogues. The multi–amino catalyst turned out to be efficient up to 1 % molar without the use of acidic additives providing the desired product in 82 % yield and maintaining good level of enantioselectivity. ESI-MS experiments together with data supplied by theoretical models allowed us the understand the operating mechanism of the catalyst, clarifying the role of the amine functions and confirming the catalyst's multifunctionality. The presence of three active catalytic sites makes it easy its anchoring to silica as solid support for applications in heterogeneous phase catalysis.

Here, we have developed an environmentally friendly and cost-effective catalyst for the alcoholysis of C−O-linked plastics. Our catalyst is made of polymeric carbon nitride nanosheets, which are free of metals. It has shown excellent performance in the methanolysis of polycarbonate (PC), polyethylene terephthalate (PET), and polylactic acid (PLA), producing pure monomer products. Through characterization and experiments, we have determined that the amino group is the main active site of the catalyst.

Abstract

Improper end-of-life treatments of C−O-linked plastics have caused serious environmental crises and resource waste. One effective method to solve this issue is the catalytic alcoholysis of these plastics. Traditional homogeneous catalysts or metal-based heterogeneous catalysts for alcoholysis have some drawbacks, such as difficulty in complete separation, environmental threats, and economic burden. Thus, finding a green, low-cost, recyclable, and highly efficient catalyst substitute is critical. Here, we reported that polymeric carbon nitride nanosheets can serve as a metal-free heterogeneous catalyst for the methanolysis of polycarbonate, polyethylene terephthalate, and polylactic acid. The catalyst exhibits remarkable performance and could be reused at least four times. NH _x was found to be the predominant active site of the catalyst by characterization and experiments. These results show promise for the design of metal-free heterogeneous catalysts to depolymerize C−O-linked plastics.