Asymmetrical electrohydrogenation of CO2 to ethanol with copper-gold heterojunctions.

Copper is distinctive in electrocatalyzing reduction of CO2 into various energy-dense forms, but it often suffers from limited product selectivity including ethanol in competition with ethylene. Here, we describe systematically designed, bimetallic electrocatalysts based on copper/gold heterojunctions with a faradaic efficiency toward ethanol of 60% at currents in excess of 500 mA cm-2. In the modified catalyst, the ratio of ethanol to ethylene is enhanced by a factor of 200 compared to copper catalysts. Analysis by ATR-IR measurements under operating conditions, and by computational simulations, suggests that reduction of CO2 at the copper/gold heterojunction is dominated by generation of the intermediate OCCOH*. The latter is a key contributor in the overall, asymmetrical electrohydrogenation of CO2 giving ethanol rather than ethylene.

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication.

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

Adsorption and activation of small molecules on boron nitride catalysts.

Hexagonal boron nitride possesses a unique layered structure, high specific surface area and similar electronic properties as graphene, which makes it not only a promising catalyst support, but also a highly effective metal-free catalyst in the booming field of green chemistry. Reactions involving small molecules (e.g., oxygen, low carbon alkanes, nitrogen and carbon dioxide) have always been a hot topic in catalytic research, especially associated with the adsorption and activation regime of different forms of small molecules on catalysts. In this review, we have investigated the adsorption of different small molecules and the relevant activation mechanisms of four typical chemical bonds (OO, C-H, NN, CO) on hexagonal boron nitride. Recent progress on approaches adopted to enhance the activation capacity such as doping, defect engineering and heterostructuring are summarized, highlighting the potential applications of nonmetallic hexagonal boron nitride catalysts in various reactions. This comprehensive investigation offers a reference point for the enhanced mechanistic understanding and future design of effective and sustainable catalytic systems based on boron nitride.

Photorefinery of Biomass and Plastics to Renewable Chemicals using Heterogeneous Catalysts.

The photocatalytic conversion of biomass and plastic waste provides opportunities for sustainable fuel and chemical production. Heterogeneous photocatalysts, typically composed of semiconductors with distinctive redox properties in their conduction band (CB) and valence band (VB), facilitate both the oxidative and reductive valorization of organic feedstocks. This article provides a comprehensive overview of recent advancements in the photorefinery of biomass and plastics from the perspective of the redox properties of photocatalysts. We explore the roles of the VB and CB in enhancing the value-added conversion of biomass and plastics via various pathways. Our aim is to bridge the gap between photocatalytic mechanisms and renewable carbon feedstock valorization, inspiring further development in photocatalytic refinery of biomass and plastics.

Acetamide Electrosynthesis from CO2 and Nitrite in Water.

Renewable electricity driven electrocatalytic CO2 reduction reaction (CO2 RR) is a promising solution to carbon neutralization, which mainly generate simple carbon products. It is of great importance to produce more valuable C-N chemicals from CO2 and nitrogen species. However, it is challenging to co-reduce CO2 and NO3 - /NO2 - to generate aldoxime an important intermediate in the electrocatalytic C-N coupling process. Herein, we report the successful electrochemical conversion of CO2 and NO2 - to acetamide for the first time over copper catalysts under alkaline condition through a gas diffusion electrode. Operando spectroelectrochemical characterizations and DFT calculations, suggest acetaldehyde and hydroxylamine identified as key intermediates undergo a nucleophilic addition reaction to produce acetaldoxime, which is then dehydrated to acetonitrile and followed by hydrolysis to give acetamide under highly local alkaline environment and electric field. Moreover, the above mechanism was successfully extended to the formation of phenylacetamide. This study provides a new strategy to synthesize highly valued amides from CO2 and wastewater.

Electrothermal Water-Gas Shift Reaction at Room Temperature with a Silicomolybdate-Based Palladium Single-Atom Catalyst.

The water-gas shift (WGS) reaction is often conducted at elevated temperature and requires energy-intensive separation of hydrogen (H2 ) from methane (CH4 ), carbon dioxide (CO2 ), and residual carbon monoxide (CO). Designing processes to decouple CO oxidation and H2 production provides an alternative strategy to obtain high-purity H2 streams. We report an electrothermal WGS process combining thermal oxidation of CO on a silicomolybdic acid (SMA)-supported Pd single-atom catalyst (Pd1 /CsSMA) and electrocatalytic H2 evolution. The two half-reactions are coupled through phosphomolybdic acid (PMA) as a redox mediator at a moderate anodic potential of 0.6 V (versus Ag/AgCl). Under optimized conditions, our catalyst exhibited a TOF of 1.2 s-1 with turnover numbers above 40 000 mol CO 2 ${{_{{\rm CO}{_{2}}}}}$ molPd -1 achieving stable H2 production with a purity consistently exceeding 99.99 %.

Overexpression of heat shock protein 70 induces apoptosis of intestinal epithelial cells in heat-stressed pigs: A proteomics approach.

Heat stress (HS)-induced intestinal epithelial cell apoptosis may play a pivotal role in intestinal barrier dysfunction in animals. However, the underlying molecular mechanism by which HS induces apoptosis in intestinal epithelial cells is still poorly understood. Herein, a eukaryotic expression vector for an HSP70 gene was constructed and transfected into intestinal porcine epithelial cells (IPEC-J2). Afterward, functional proteomics approaches followed by liquid-chromatography-tandem mass spectrometry (LC-MS/MS) were used to identify interacting proteins. Analysis of HSP70 transfected IPEC-J2 cells revealed 246 differentially expressed proteins (DEPs), and functional annotation indicated that most DEPs were primarily related to ECM-receptor interaction, focal adhesion, and apoptosis. Furtherly, the apoptosis rate and expression levels of apoptosis-related proteins in HSP70 transfected IPEC-J2 cells were detected, we found that the expression of caspase-3, PARP, and Bax were increased, but Bcl-2 were decreased in transfected cells. Lastly, an in vitro and in vivo heat stress model were established to explore the role of HSP70 in intestinal epithelia cell apoptosis. The results of in vitrol study showed that HS-induced cellular apoptosis and increases of caspase-3, PARP, and Bax, but decreased of Bcl-2 in IPEC-J2 cells. In vivo study, the cell apoptosis were induced significantly in the duodenum, cecum, and colon of heat stressed pigs, and upregulation of HSP70 was also detected in colon tissues. Therefore, it has been shown that HSP70 plays a crucial role in heat stress-induced apoptosis and may provide new insights into the molecular mechanisms of epithelial cell apoptosis induced by heat stress in pigs.

Copper-Catalyzed and Proton-Directed Selective Hydroxymethylation of Alkynes with CO2.

An intriguing strategy for copper-catalyzed hydroxymethylation of alkynes with CO2 and hydrosilane was developed. Switched on/off a proton source, for example, t BuOH, direct hydroxymethylation and reductive hydroxymethylation could be triggered selectively, delivering a series of allylic alcohols and homobenzylic alcohols, respectively, with high levels of Z/E, regio- and enantioselectivity. Such a selective synthesis is attributed to the differences in response of vinylcopper intermediate to proton and CO2 . The protonation of vinylcopper species is demonstrated to be prior to hydroxymethylation, thus allowing a diversion from direct alkyne hydroxymethylation to reductive hydroxymethylation in the presence of suitable proton.

Template-induced Al distribution in MOR and enhanced activity in dimethyl ether carbonylation.

As the activity of dimethyl ether (DME) carbonylation over mordenite proportionally correlates with the Brønsted acid sites (BAS) in 8-membered ring (8-MR), enhancing the concentration of BAS in the 8-MR of MOR is important to improve the efficiency of the reaction. Herein, we report that the distribution of the BAS in the zeolite catalyst H-MOR can be altered by the synthesis of H-MOR with different cyclic amine structure-directing templates, several of which have not been reported previously for MOR synthesis. By combining FTIR, ICP, TG analysis and DFT calculations, it is verified that the strength of the interaction between amine or sodium cations and [AlO4]- in the zeolite framework plays a decisive role in Al distribution, owing to the competitive effect between Na+ and the cyclic amine compensating negative charges from the framework [AlO4]-. Quantitative analysis of the BAS in the 12-MR and 8-MR identifies the optimum template for maximizing the BAS in the 8-MR. It is shown that the enhanced activity of the H-MOR for the DME carbonylation to methyl acetate correlates with the increase in the BAS in the 8-MR. Our finding thus provides a facile strategy to direct Al location within different channels of the zeolite, which must benefit spatially confined reaction systems.

Recent advances in dialkyl carbonates synthesis and applications.

Dialkyl carbonates are important organic compounds and chemical intermediates with the label of "green chemicals" due to their moderate toxicity, biodegradability for human health and environment. Indeed, owing to their unique physicochemical properties and versatility as reagents, a variety of phosgene-free processes derived from CO or CO2 have been explored for the synthesis of dialkyl carbonates. In this critical review, we highlight the recent achievements (since 1997) in the synthesis of dialkyl carbonates based on CO and CO2 utilization, particularly focusing on the catalyst design and fabrication, structure-function relationship, catalytic mechanisms and process intensification. We also provide an overview regarding the applications of dialkyl carbonates as fuel additives, solvents and reaction intermediates (i.e. alkylating and carbonylating agents). Additionally, this review puts forward the substantial challenges and opportunities for future research associated with dialkyl carbonates.

An alternative synthetic approach for efficient catalytic conversion of syngas to ethanol.

Ethanol is an attractive end product and a versatile feedstock because a widespread market exists for its commercial use as a fuel additive or a potential substitute for gasoline. Currently, ethanol is produced primarily by fermentation of biomass-derived sugars, particularly those containing six carbons, but coproducts 5-carbon sugars and lignin remain unusable. Another major process for commercial production of ethanol is hydration of ethylene over solid acidic catalysts, yet not sustainable considering the depletion of fossil fuels. Catalytic conversion of synthetic gas (CO + H2) could produce ethanol in large quantities. However, the direct catalytic conversion of synthetic gas to ethanol remains challenging, and no commercial process exists as of today although the research has been ongoing for the past 90 years, since such the process suffers from low yield and poor selectivity due to slow kinetics of the initial C-C bond formation and fast chain growth of the C2 intermediates. This Account describes recent developments in an alternative approach for the synthesis of ethanol via synthetic gas. This process is an integrated technology consisting of the coupling of CO with methanol to form dimethyl oxalate and the subsequent hydrogenation to yield ethanol. The byproduct of the second step (methanol) can be separated and used in circulation as the feedstock for the coupling step. The coupling reaction of carbon monoxide for producing dimethyl oxalate takes place under moderate reaction conditions with high selectivity (∼95%), which ideally leads to a self-closing, nonwaste, catalytic cycling process. This Account also summarizes the progress on the development of copper-based catalysts for the hydrogenation reaction with remarkable efficiencies and stability. The unique lamellar structure and the cooperative effect between surface Cu(0) and Cu(+) species are responsible for the activity of the catalyst with high yield of ethanol (∼91%). The understanding of nature of valence states of Cu could also guide the rational design of Cu-based catalysts for other similar reactions, particularly for hydrogenation catalytic systems. In addition, by regulating the reaction condition and the surface structure of the catalysts, the products in the hydrogenation steps, such as ethanol, methyl glycolate, and ethylene glycol, could be tuned efficiently. This synthetic approach enables a more sustainable ethanol, methyl glycolate, and ethylene glycol synthesis in industry and greatly reduces the dependence on petroleum resources and the emission of the greenhouse gas.

Effect of cerium oxide doping on the performance of CaO-based sorbents during calcium looping cycles.

A series of CaO-based sorbents were synthesized through a sol-gel method and doped with different amounts of CeO2. The sorbent with a Ca/Ce molar ratio of 15:1 showed an excellent absorption capacity (0.59 gCO2/g sorbent) and a remarkable cycle durability (up to 18 cycles). The admirable capture performance of CaCe-15 was ascribed to its special morphology formed by the doping of CeO2 and the well-distributed CeO2 particles. The sorbents doped with CeO2 possessed a loose shell-connected cross-linking structure, which was beneficial for the contact between CaO and CO2. CaO and CeO2 were dispersed homogeneously, and the existence of CeO2 also decreased the grain size of CaO. The well-dispersed CeO2, which could act as a barrier, effectively prevented the CaO crystallite from growing and sintering, thus the sorbent exhibited outstanding stability. The doping of CeO2 also improved the carbonation rate of the sorbent, resulting in a high capacity in a short period of time.

Boosting CO2 electrocatalysis through electrical double layer regulations.

Interfacial investigation for fine-tuning microenvironment has recently emerged as a promising method to optimize the electrochemical CO2 reduction system. The electrical double layer located at the electrode-electrolyte interface presents a particularly significant impact on electrochemical reactions. However, its effect on the activity and selectivity of CO2 electrocatalysis remains poorly understood. Here, we utilized two-dimensional mica flakes, a material with a high dielectric constant, to modify the electrical double layer of Ag nanoparticles. This modification resulted in a significant enhancement of current densities for CO2 reduction and an impressive Faradaic efficiency of 98% for CO production. Our mechanistic investigations suggest that the enhancement of the electrical double layer capacitance through mica modification enriched local CO2 concentration near the reaction interface, thus facilitating CO2 electroreduction.

Understanding electronic and optical properties of anatase TiO2 photocatalysts co-doped with nitrogen and transition metals.

This paper describes an investigation into the general trend in electronic properties of anatase TiO2 photocatalysts co-doped with transition metals and nitrogen employing first-principles density functional theory. Fourteen different transition metals (M), including Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, and Cd, have been considered. The characteristic band structures of the co-doping systems involving the transition metal series are presented. Our results indicate that the absorption edges of TiO2 are shifted to the visible-light region upon introduction of dopants, due to the reduced conduction band minimum (CBM) and the formation of impurity energy levels (IELs) in the band gap. These IELs are primarily formed from (a) the anti-bonding orbitals of the M-O (M indicates the doped transition metal) bonds, (b) the unsaturated nonbonding d orbitals of the doped transition metal (mainly d(xy), d(yz), and d(xz)), and (c) the Ti-O bonding/Ti-N anti-bonding orbitals of the bond next to the doped transition metal. When the valence d electrons of the doped metal are between 3 and 7, all three types of IELs appear in the band gap of the (M, N) co-doped systems. For systems doped with a metal of more than 7 valence electrons, only types (a) and (c) of IELs as well as the unoccupied pz state of N are observed. Based on our analysis, we propose that the co-doping systems such as (V, N), (Cr, N), and (Mn, N), which have the IELs with a significant bandwidth, are of great potential as candidates for photovoltaic applications in the visible light range.

DFT investigations for the reaction mechanism of dimethyl carbonate synthesis on Pd(II)/ß zeolites.

Density functional theory (DFT) calculations have been used to investigate the oxidative carbonylation of methanol on Pd(II)/ß zeolite. Activation energies for all the elementary steps involved in the commonly accepted mechanism, including the formation of dimethyl carbonate, methyl formate and dimethoxymethane, are presented. Upon conducting the calculations, we identify that the Pd(2+) cation bonded with four O atoms of the zeolite framework acts as the active site of the catalyst. Molecularly adsorbed methanol starts to react with oxygen molecules to produce a methanediol intermediate (CH2(OH)2) and O atom. Then, another methanol can react with the O atom to produce the (CH3O)(OH)-Pd(II)/ß zeolite species. (CH3O)(OH)-Pd(II)/ß zeolite can further react with carbon monoxide or methanol to give monomethyl carbonate or di-methoxide species ((CH3O)2-Pd(II)/ß zeolite). Dimethyl carbonate can form via two distinct reaction pathways: (I) methanol reacts with monomethyl carbonate or (II) carbon monoxide inserts into di-methoxide. Our calculation results show the activation energy of reaction (I) is too high to be achieved. The methanediol intermediate is unstable and can decompose to formaldehyde and H2O immediately. Formaldehyde can either react with an O atom or methanol to form formic acid or a CH3OCH2OH intermediate. Both of them can react with methanol to form the secondary products (methyl formate or dimethoxymethane). Upon conducting calculations, we confirmed that the activation energies for the formation of methyl formate and dimethoxymethane are higher than that of dimethyl carbonate. All these conformations were characterized at the same calculation level.

Branched TiO2 nanoarrays sensitized with CdS quantum dots for highly efficient photoelectrochemical water splitting.

This paper describes the design, characterization, and utilization of branched TiO2 nanoarrays sensitized with CdS quantum dots as anodes for photoelectrochemical water splitting. The remarkable photocurrent density (∼4 mA cm(-2) at a potential of 0 V versus Ag/AgCl) and high solar to hydrogen efficiency of the materials obtained were ascribed to the novel branched nanostructure and efficient electron transfer from CdS to TiO2.

Ethylene glycol: properties, synthesis, and applications.

Ethylene glycol (EG) is an important organic compound and chemical intermediate used in a large number of industrial processes (e.g. energy, plastics, automobiles, and chemicals). Indeed, owing to its unique properties and versatile commercial applications, a variety of chemical systems (e.g., catalytic and non-catalytic) have been explored for the synthesis of EG, particularly via reaction processes derived from fossil fuels (e.g., petroleum, natural gas, and coal) and biomass-based resources. This critical review describes a broad spectrum of properties of EG and significant advances in the prevalent synthesis and applications of EG, with emphases on the catalytic reactivity and reaction mechanisms of the main synthetic methodologies and applied strategies. We also provide an overview regarding the challenges and opportunities for future research associated with EG.

Self-Supported Porous Carbon Nanofibers Decorated with Single Ni Atoms for Efficient CO2 Electroreduction.

Single-atom catalysts within M-N-C structures are efficient for electrochemical CO2 reduction. However, most of them are powdered and require a coating process to load on the electrode. Herein, we developed a facile approach to the synthesis of large-scale self-supported porous carbon nanofiber electrodes directly decorated with atomically dispersed nickel active sites using facile electrospinning, where poly(methyl methacrylate) was employed to tune well the distributions of pores located in carbon nanofibers. The above self-supported carbon nanofibers were applied as a gas diffusion electrode to achieve 94.3% CO Faraday efficiency and 170 mA cm-2 current density, which can be attributed to the effects of rich mesoporous structures favorable for adsorption and mass transfer of CO2 and single nickel catalysts effectively converting CO2 to CO. This work provides an efficient strategy to fabricate self-supported electrodes and may accelerate the progress toward industrial applications of single-atom catalysts in the field of CO2 electroreduction.

Electrosynthesis of ethylene glycol from C1 feedstocks in a flow electrolyzer.

Ethylene glycol is a widely utilized commodity chemical, the production of which accounts for over 46 million tons of CO2 emission annually. Here we report a paired electrocatalytic approach for ethylene glycol production from methanol. Carbon catalysts are effective in reducing formaldehyde into ethylene glycol with a 92% Faradaic efficiency, whereas Pt catalysts at the anode enable formaldehyde production through methanol partial oxidation with a 75% Faradaic efficiency. With a membrane-electrode assembly configuration, we show the feasibility of ethylene glycol electrosynthesis from methanol in a single electrolyzer. The electrolyzer operates a full cell voltage of 3.2 V at a current density of 100 mA cm-2, with a 60% reduction in energy consumption. Further investigations, using operando flow electrolyzer mass spectroscopy, isotopic labeling, and density functional theory (DFT) calculations, indicate that the desorption of a *CH2OH intermediate is the crucial step in determining the selectively towards ethylene glycol over methanol.

Scalable synthesis of Cu clusters for remarkable selectivity control of intermediates in consecutive hydrogenation.

Subnanometric Cu clusters that contain only a small number of atoms exhibit unique and, often, unexpected catalytic behaviors compared with Cu nanoparticles and single atoms. However, due to the high mobility of Cu species, scalable synthesis of stable Cu clusters is still a major challenge. Herein, we report a facile and practical approach for scalable synthesis of stable supported Cu cluster catalysts. This method involves the atomic diffusion of Cu from the supported Cu nanoparticles to CeO2 at a low temperature of 200 °C to form stable Cu clusters with tailored sizes. Strikingly, these Cu clusters exhibit high yield of intermediate product (95%) in consecutive hydrogenation reactions due to their balanced adsorption of the intermediate product and dissociation of H2. The scalable synthesis strategy reported here makes the stable Cu cluster catalysts one step closer to practical semi-hydrogenation applications.