Converting CO2 into valuable chemicals has been intensively explored in recent years. Benefited from the substantial cost reduction of renewable electricity, the electrochemical methods have been emerging as a potential means for CO2 capture and conversion. Recently, molecular tuning has been recognized as a powerful technique to modify catalyst’s surface and verified effective in improving CO2RR performance. However, there are few comprehensive and insightful reviews on molecularly modified Cu-based catalysts to precisely modulate the activity and selectivity of C2+ products in CO2 reduction. Herein, the development of CO2RR plausible reaction mechanisms is first introduced. The process and reaction pathways of the carbon-carbon coupling are briefly discussed. Four main aspects of the molecular tuning strategy of the CO2RR are described as the first coordination layer, second coordination layer, outer-layer, and confined effects. The understanding of the improved C2+ performance is demonstrated for molecularly modified Cu-based catalysts. The challenges and perspectives in this field are addressed to further inspire the disclosure of the fundamental understanding in CO2RR, the system optimization, advanced in situ and operando techniques, and integration of CO2 capture and conversion technology with high activity and selectivity for durable applications.

The use of ZrO2 as a support material for IrOx-based catalysts in oxygen evolution reaction (OER) electrocatalysis was studied using ex-situ characterization and rotating disk electrode electrochemical testing of supported IrxZr(1-x)O2 on ZrO2 of varying sizes. The catalyst exhibited high OER mass (specific) activity (712 A.gIr-1) and intrinsic activity (4.8 mA.cmECSA-2) at 1.6 VRHE, attributed to IrxZr(1-x)O2 alloy formation, an interconnected network of IrxZr(1-x)O2 nanoparticles and the presence of Ir(III)/Ir(IV) species throughout the bulk. It also appears to be resistant to Ir dissolution; however, accumulation of O2 bubbles and minor phase transformation of Ir(III)/Ir(IV) species during OER cause deactivation. Temperature-programmed desorption indicated a possible link between the observed high activity and higher amounts of adsorbed H2O and desorbed O2 species.

Mechanoenzymatic reactions are promising strategy for designing more sustainable processes. As mechanochemistry is already more explored mechanoenzymology can apply those lessons in enzymatic process development. Different devices for mechanoenzymology are discussed and their use in a rational process development. Mechanoenzymology may benefit from recent developments in mechanochemistry in the areas of process design and in-line analytics.

Abstract

Mechanoenzymology has emerged as a recent topic in modern research and process design in the transition towards green chemistry. Due to the almost solvent-free character of mechanoenzymatic reactions solvent usage is considerably reduced and waste can be avoided. Moreover, mechanoenzymatic reactions show highly promising space-time yields and conversions, however, are still less investigated than their chemical counterparts. The selectivity of enzymes is an important feature for designing green processes and avoiding formation of by-products. In this review, different mechanoenzymatic strategies are pointed out, involving the most common applied devices, i. e., shaker ball mills, planetary ball mills and twin-screw extruders. Their compatibility with upscaling and continuous processes is discussed and reusability of enzymes in the different mechanoenzymatic processes is evaluated. In addition, learnings from mechanochemistry are presented and their potential benefits for mechanoenzymology are outlined.

The selective reduction of terminal alkynes to alkenes was investigated using common cationic diphosphane rhodium complexes of the type [Rh(PP)(diolefin)]X (PP = diphosphane, X = anion). The effectiveness of the catalyst was demonstrated in the semi-hydrogenation of, dehydroisophytol (DIP), an industrial produced intermediate of vitamin E. The present study highlights the high activity and good selectivity of this simple catalytic system. However, deactivation increases at higher DIP concentrations. Several strategies to circumvent the deactivation are presented.

Selective hydrogenation: Encapsulated Pt@SOD catalyst exhibited 100 % selectivity in hydrogenation of p-chloronitrobenzene to p-chloroaniline via the discrimination of the hydrogenation rate of separated nitro group and separated C−Cl group during the hydrogen spillover process.

Abstract

Herein, we reported that the platinum (Pt) clusters encapsulated into sodalite (SOD) zeolite as catalyst exhibited 100 % selectivity at 100 % conversion in the selective hydrogenation of p-chloronitrobenzene to p-chloroaniline via hydrogen spillover. The direct interaction between p-chloronitrobenzene and encapsulated Pt was prevented by the shape selectivity of SOD zeolite, reactants were thereby adsorbed onto zeolite outer surface to facilitate the hydrogenation proceeding by hydrogen spillover process. The further kinetic study and DFT calculation showed the excellent catalytic selectivity was ascribed to the much faster rate of hydrogenation of adsorbed nitro group than that of adsorbed C−Cl group.

CO₂ Reforming: Transition metal-based SiO₂-Ni@CeO₂ catalyst with typical core@shell structure exhibited the better activity/stability in CO₂ reforming with ethanol reaction compared to SiO₂-Cu@CeO₂ sample.

Abstract

It is of great significance to design the high-performance catalysts with good anti-sintering and coke-resistance properties which can efficiently convert undesirable greenhouse gas CO₂ with bio-ethanol into high value-added syngas. To be addressed this issue, a series of SiO₂-M@CeO₂ (M: Cu, Ni) catalysts with typical core@shell structure were prepared via a strong electrostatic adsorption technique. Interestingly, Ni-based catalyst exhibited the higher activity towards ethanol dry reforming at the relatively low temperature. Meanwhile, SiO₂-Ni@CeO₂ catalyst presented good stability after a 50 h tests while a serious deactivation occurred for SiO₂-Cu@CeO₂ within 20 h reaction due to heavy carbon deposition and reactor blockage. Herein, the higher catalytic performance of SiO₂-Ni@CeO₂ catalyst compared to SiO₂-Cu@CeO₂ sample was attributed to the combination effect of its mesoporous structure, higher Ni dispersion as well as stronger Ni-Ce interaction as depicted by BET, TEM, XPS, H₂-TPR and XRD findings. This work might provide meaningful information to other reforming processes involving coke formation and active metal sintering problems.

The Front Cover illustrates a tug-of-war played between two concomitant but opposite effects brought forth by the presence of H₂O in the Reduction Half-Cycle (RHC) of NH₃-SCR, leading to a reduction in both the rate and its apparent activation energy with respect to dry conditions. In their Research Article, M. Maestri, E. Tronconi and co-workers show that such phenomena are a consequence of enthalpic stabilization and additional entropic penalties of the TS brought forth by the presence of H₂O in the cage of Cu-CHA. This result thus provides a theoretical understanding of the kinetic role of H₂O in the RHC, highlighting the importance of the molecular scale description of the reaction environment in voids of molecular dimensions. Image credit: Gabriele Contaldo and Lia Tagliavini. More information can be found in the Research Article by M. Maestri, E. Tronconi and co-workers.

The Cover Feature represents two different roads available to carry out the N-alkylation of amines with alcohols. The first road is wide and taken by many people; it consists of transition metal catalysis operating via the well-known “borrowing-hydrogen” pathway. In contrast, the findings reported by M. T. Johnson, O. F. Wendt and co-workers in their Research Article lays out a road less travelled, using the presence of air along with catalytic amount of base to reach the final goal. As indicated by the magnification, the methodology has a broader scope than shown and can be applied to similar reactions, one example in the report being the β-alkylation of secondary alcohols with primary alcohols. More information can be found in the Research Article by M. T. Johnson, O. F. Wendt and co-workers.

Herein we synthesized a panel of non-canonical amino acids (ncAAs) harboring functional secondary amines inspired by organocatalysts. After their synthesis and characterization, D/L-pyrrolidine- and D/L-piperidine-based ncAAs were successfully site-specifically incorporated into proteins via stop codon suppression methodology. To demonstrate the utility of these ncAAs, the catalytic performance of the obtained artificial enzymes was investigated in a model Michael addition reaction.

Abstract

Enzymes are attractive catalysts for chemical industries, and their use has become a mature alternative to conventional chemical methods. However, biocatalytic approaches are often restricted to metabolic and less complex reactivities, given the limited amount of functional groups present. This drawback can be addressed by incorporating non-canonical amino acids (ncAAs) harboring new-to-nature chemical groups. Inspired by organocatalysis, we report the design, synthesis and characterization of a panel of ncAAs harboring functional secondary amines and their cellular incorporation into different protein scaffolds. D/L-pyrrolidine- and D/L-piperidine-based ncAAs were successfully site-specifically incorporated into proteins via stop codon suppression methodology. To demonstrate the utility of these ncAAs, the catalytic performance of the obtained artificial enzymes was investigated in a model Michael addition reaction. The incorporation of pyrrolidine- and piperidine- based ncAAs significantly expands the available toolbox for protein engineering and chemical biology applications.