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In the electrocatalytic CO2 reduction reaction (CO2RR), metal catalysts with an oxidation state generally demonstrate more favorable catalytic activity and selectivity than their corresponding metallic counterparts. However, the persistence of oxidative metal sites under reductive potentials is challenging since the transition to metallic states inevitably leads to catalytic degradation. Herein, a thorough review of research on oxidation-state stabilization in the CO2RR is presented, starting from fundamental concepts and highlighting the importance of oxidation state stabilization while revealing the relevance of dynamic oxidation states in product distribution. Subsequently, the functional mechanisms of various oxidation-state protection strategies are explained in detail, and in situ detection techniques are discussed. Finally, the prevailing and prospective challenges associated with oxidation-state protection research are discussed, identifying innovative opportunities for mechanistic insights, technology upgrades, and industrial platforms to enable the commercialization of the CO2RR. [ABSTRACT FROM AUTHOR]

The lateral size of graphene nanosheets plays a critical role in the properties and microstructure of 3D graphene as well as their application as supports of electrocatalysts for CO2 reduction reactions (CRRs). Here, graphene oxide (GO) nanosheets with different lateral sizes (1.5, 5, and 14 µm) were utilized as building blocks for 3D graphene aerogel (GA) to research the size effects of GO on the CRR performances of 3D Au/GA catalysts. It was found that GO-L (14 µm) led to the formation of GA with large pores and a low surface area and that GO-S (1.5 µm) induced the formation of GA with a thicker wall and isolated pores, which were not conducive to the mass transfer of CO2 or its interaction with catalysts. Au/GA constructed with a suitable-sized GO (5 µm) exhibited a hierarchical porous network and the highest surface area and conductivity. As a result, Au/GA-M exhibited the highest Faradaic efficiency (FE) of CO (FECO = 81%) and CO/H2 ratio at −0.82 V (vs. a Reversible Hydrogen Electrode (RHE)). This study indicates that for 3D GA-supported catalysts, there is a balance between the improvement of conductivity, the adsorption capacity of CO2, and the inhibition of the hydrogen evolution reaction (HER) during the CRR, which is related to the lateral size of GO. [ABSTRACT FROM AUTHOR]

CO2 hydrogenation to methanol was conducted using a set of activated carbon-supported Cu/ZnO/Al2O3 catalysts (CCZA) prepared by an incipient wetness impregnation approach. The effect of the Cu/Al ratio on the physicochemical properties of the catalysts, as well as their catalytic performance, were investigated. As Cu/Al ratio increased, the metallic Cu surface area displayed a reducing trend from 6.88 to 4.18 m2∙gcat−1, while the CO2 adsorption capacity exhibited an increasing trend. Meanwhile, aluminum content will have an important effect on the catalysts' reducibility and, thus, on their catalytic performance. The CCZA-2.7-de catalyst demonstrated the highest selectivity to methanol at 83.75% due to the excellent distribution and synergistic effect of copper and zinc. Although the CO2 conversion of CCZA-2.2-de and CCZA-3.5-de exceeded 10%, the CH3OH selectivity was less than 60%, which may be attributed to the larger particle sizes of ZnO and poor interactions in Cu–Zn. The present study offers a novel approach to increase the number of active sites, optimize the activated carbon-aided Cu/ZnO/Al2O3 catalyst's composition, and finally elucidate the mechanism for CO2 hydrogenation to methanol. [ABSTRACT FROM AUTHOR]

Herein, atomically dispersed Ni–N 3 –C materials are facilely synthesized by the pyrolysis of Ni-doped ZIF-8. Each single Ni atom is proved to be bonded with three N atoms to form Ni–N 3 sites by X-ray absorption spectroscopy. During the pyrolysis at high temperature, the increasing of relative contents and blue-shift binding energy of pyrrolic N can be observed, indicating the Ni might be bonded with pyrrolic N. Moreover, the formation energy (E f) of NiN 3 -pyrrolic structure is smaller than that of NiN 3 -pyridinic calculated by density functional theory (DFT), thus confirming the dominated bonding structure of NiN 3 -pyrrolic further. The optimum material can achieve an ultra-high CO Faradaic efficiency of 99.37% at −0.75 V vs. RHE with a turnover frequency (TOF) of 3498 h−1 and a high CO partial current density of 80 mA cm−2 at −1.15 V vs. RHE, which is among the best Ni catalysts. Based on DFT results, the NiN 3 -pyrrolic sites can facilitate both the formation of COOH* intermediate and desorption of CO, which can also suppress the competitive hydrogen evolution reaction (HER) simultaneously, thus resulting in high catalytic activity and selectivity from CO 2 to CO. Electroreduction from CO 2 to CO with high activity and selectivity are achieved on the single-atom Ni–N–C catalyst due to the dominated Ni coordination structure by three pyrrolic N atoms. [Display omitted] • Single Ni atom catalysts were synthesized with Ni-doped ZIF-8 as precursor. • NiN 3 -pyrrolic coordination structure was identified as the dominated active sites. • Ultra-high activity and selectivity for CO 2 reduction towards CO was achieved. • NiN 3 -pyrrolic sites can promote the formation of *COOH intermediate by DFT. [ABSTRACT FROM AUTHOR]

The development of Ni-based catalysts with outstanding anti-coking ability is necessary for realizing the industrial application of dry reforming of CH 4 (DRM) to syngas. Here, a facile combustion method with unique characteristic was employed to prepare the Ni/SiO 2 catalyst with different promoters (ZrO 2 or Ru). The effects of Ni particle size and promoter (ZrO 2 or Ru) on the anti-coking ability of Ni/SiO 2 catalyst were examined. The XRD and TEM results showed that improved Ni dispersion can be obtained via the facile combustion method, accompanying with enhanced metal-support interaction and CO 2 adsorption capacity confirmed by H 2 -TPR and CO 2 -TPD, respectively. In comparison with Ni-IMP catalyst (prepared via the traditional impregnation method), the carbon deposition over Ni–C catalyst (prepared via the combustion method) decreased by 67% (from 2.7 to 0.9 mg carbon deposition ·g−1 CH4) as a result of the small Ni particles. The H 2 -TPR and XPS results revealed the interaction between promoter (ZrO 2 and Ru) and Ni. The addition of ZrO 2 can enhanced the CO 2 activation ability of catalyst and the formed oxygen species can facilitate the elimination of carbon species, further decreasing the carbon deposition compared with Ni–C catalyst. The best catalytic performance with least carbon deposition (only 0.4 mg carbon deposition ·g−1 CH4) is achieved on the NiRu–C catalyst. The slower CH 4 dissociation rate and the improved CO 2 activation benefited from Ru can bring in the better balance between the carbon formation and elimination, leading to the best anti-coking ability of catalyst. [Display omitted] • Highly dispersed Ni particles are obtained by a combustion method with low cost. • Excellent catalytic stability is achieved on the catalyst with small Ni particles. • ZrO 2 can enhance the CO 2 activation and facilitate the elimination of carbon species. • NiRu/SiO 2 catalyst can balance CH 4 and CO 2 activation, minimizing the coke formation. [ABSTRACT FROM AUTHOR]

A simple one‐pot method has been developed to synthesize a palladium/cuprous oxide‐copper (Pd/Cu2O–Cu) material with a well‐defined structure, by modification of Cu2O–Cu with Pd through a galvanic replacement reaction. Compared with the well‐known copper/cuprous oxide (Cu/Cu2O) catalysts, the Pd/Cu2O–Cu material can catalyze the electroreduction of CO2 into C1 products with much higher faradaic efficiencies at lower overpotentials in a CO2‐saturated 0.5 m NaHCO3 solution. In particular, the highest faradaic efficiencies of 92 % for formate and 30 % for methane were achieved at −0.25 and −0.65 V (vs. the reversible hydrogen electrode), respectively. The improvement is suggested to be the result of a synergistic effect between PdH and the catalytically active copper sites during electrochemical CO2 reduction. [ABSTRACT FROM AUTHOR]

Abstract: In recent years increasing attention has been given to the efficacious synthesis of organic carbonates from sustainable CO2. The carboxylation/hydration reaction of alcohols with CO2 stands out for its environmentally friendly and economic features. However, it faces several substantial challenges such as thermodynamic limitations, low catalytic efficiency, and product selectivity. In this article, recent advances in the development of catalytic methods for the synthesis of organic carbonates through carboxylation/hydration reaction of alcohols with CO2 are summarized. Catalytic schemes (metal and metal‐free catalysis), water‐dehydration strategies, and catalytic mechanisms are also discussed in detail. The review covers the carbonylation cyclization of various alcohols and the equivalent of CO2, i.e. urea. Finally, an overview is provided of the recent breakthrough in the development of thermodynamically favorable processes involving alcohols and CO2. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

CO 2 methanation is conducive to the storage of renewable electricity and the utilization of CO 2. Exploiting highly efficient Ni-based catalysts with a simple method is of significance for this reaction. To achieve an excellent low-temperature activity, the attention is focused on the small Ni particles and ZrO 2 promoter in this work, which can increase the amounts of H 2 and CO 2 active sites. Firstly, the simple combustion-impregnation method was employed, forming small Ni particles (about 6 nm). More metal-support interface and increased basicity could be generated in the meantime. Hence, the higher H 2 dissociation and CO 2 adsorption ability were attained. Secondly, ZrO 2 serving as a promoter was beneficial to the formation of oxygen vacancies, which played an important role in CO 2 activation and CH 4 formation. These oxygen vacancies could weaken the C O bonds, improving the CO 2 activation. In addition, they might serve as the H reservoir, increasing the H 2 adsorption capacity. Because of the H spillover effect from Ni to ZrO 2 , the activated H atoms on Ni could react with activated CO 2 to generate CH 4. Therefore, with more active sites for H 2 and CO 2 activation, the Ni/ZrO 2 -COM catalyst exhibited the excellent catalytic performance at 300 °C. This work is of great significance in developing highly efficient Ni-based catalysts at low temperatures for CO 2 methanation with a facile method. [Display omitted] • Highly dispersion Ni particles are achieved by the combustion-impregnation method. • Oxygen vacancies benefiting to CO 2 activation are created by ZrO 2 promoter. • The best catalytic activity is obtained on the Ni/ZrO 2 -COM catalyst. • The simultaneously increased active sites for H 2 and CO 2 play an important role. [ABSTRACT FROM AUTHOR]

Plasma catalysis technology is suitable for the emission control of low concentration volatile organic compounds (VOCs), but the energy cost and complete oxidation are the bottleneck for its application. Herein, MnOx/γ-Al 2 O 3 catalysts incorporated with small amounts of Pt nano particles were designed for plasma catalytic oxidation of o-xylene which is one typical kind of VOCs from paint industry. A dielectric barrier discharge reactor installed with Pt 0.1 Mn 6 /γ-Al 2 O 3 catalyst can decompose 90% o-xylene oxidation with 90% CO 2 selectivity at an energy density of 211 J/L and a reaction temperature of 150 °C, while only 29% o-xylene conversion and 5% CO 2 selectivity were obtained without discharges under the same reaction condition. The energy cost is as high as 12.3 g/kWh which is reached top level at the same VOCs concentration. The excellent performance of Pt@MnOx/γ-Al 2 O 3 catalyst is due to the synergistic effect of Pt nano particles and MnOx, which promoted the activation of O 2 and the complete oxidation to CO 2 of by-products. [Display omitted] • High performance of plasma catalytic oxidation of o-xylene was obtained. • Pt-MnOx bimetallic interface played a dominant role in o-xylene oxidation. • Pt 0.1 Mn 6 /γ-Al 2 O 3 had highest ratios of Pt0/(Pt0 + Pt2+), Mn4+/(Total Mn) and O ads /O latt. • Pt 0.1 Mn 6 /γ-Al 2 O 3 enhanced the generation of surface reactive oxygen species. • Pt 0.1 Mn 6 /γ-Al 2 O 3 promoted the gasification of surface carbonates to gaseous CO 2. [ABSTRACT FROM AUTHOR]

A study on Pr or Ce modified hexaaluminates, La xA1 − xNiAl11O19 as catalysts for carbon dioxide reforming of methane was carried out by means of XRD, TGA, XPS and TPR techniques. The experimental results indicate that the catalytic properties of the La11O19 as catalysts for carbon dioxide reforming of methane was carried out by means of XRD, TGA, XPS and TPR techniques. The experimental results indicate that the catalytic properties of the La0.8Pr0.2 NiAl11O19 are more optimal than those of the La0.8Ce0.2. These catalysts were studied in more detail and it was found that the active nickel phase strongly depends on the interactions of the Ni ion and the La ion, which are related to the additives (Ce, Pr). [ABSTRACT FROM AUTHOR]11O19. These catalysts were studied in more detail and it was found that the active nickel phase strongly depends on the interactions of the Ni ion and the La ion, which are related to the additives (Ce, Pr). [ABSTRACT FROM AUTHOR]

Cu/ZnO/Al 2 O 3 catalysts have been widely applied as industrial catalysts for methanol synthesis from syngas, but suffers low activity for CO 2 hydrogenation to methanol. This study establishes highly active Cu catalysts through modulation of the composite of Al 2 O 3 and ZrO 2 in Cu/ZnO-based catalysts. The composition of Al 2 O 3 and ZrO 2 impacts the Cu dispersion, exposed surface area of Cu, the Cu0/(Cu0+Cu+) ratio and surface basicity. An appropriate content of Al 2 O 3 and ZrO 2 presents the higher Cu surface area, desirable ratio of Cu0/(Cu0+Cu+) and moderate-strong basic sites for effective CO 2 adsorption/activation, giving rise to higher space-time yield of methanol (up to 648 g CH3OH ·kg cat −1·h−1) than the commercial Cu catalyst. STY of methanol can be correlated with Cu surface area and Cu0/(Cu0+Cu+) ratio under the investigated conditions. The mechanistic analysis demonstrates that surface formate and methoxy species are the major intermediates. The methanol formation principally follows the formate-methoxy intermediate pathway. [Display omitted] • An appropriate amount of Al 2 O 3 and ZrO 2 favors the production of methanol. • The conversion rate of CO 2 is positively correlated with S Cu. • The relatively high content of Cu0 showed higher activity. • The increase of the number of moderate basic sites contributes to the improvement of CO 2 conversion rate. • The CO 2 hydrogenation to methanol followed the formate intermediate pathway. [ABSTRACT FROM AUTHOR]

Mn-promoted NiMgAl mixed-oxide (NiMnx-LDO, x = 0, 5, 10, 15) catalysts derived from hydrotalcite were synthesized using co-precipitation for CO 2 hydrogenation to synthetic natural gas. By regulating Mn contents, NiMn5-LDO delivered the most excellent catalytic performance, being about 2 times higher than that of undoped NiMn0-LDO catalyst (TOF of NiMn5-LDO and NiMn0-LDO: 0.61 s−1 vs 0.31 s−1 @ 240 °C). Through extensive characterization, it was found that Mn dopants promoted the reduction of bulk NiO through tuning the interaction between Ni and Mg(Mn)AlOx support. A high surface ratio of Ni0/Ni2+ was achieved over NiMn5-LDO. Furthermore, the surface basicity strength was tailored by Mn dopants. With 5 wt% of Mn, NiMn5-LDO catalyst showed a stronger medium-strength basicity and higher capacity of CO 2 adsorption than others. Particularly, TOF indicates a good correlation with medium-strength basicity over NiMnx-LDO catalysts. The strong metal-support interaction originated from the hydrotalcite structure kept nickel uniformly dispersed, endowing to the improved catalytic performance. [Display omitted] • Mn-promoted NiMnx-LDO catalysts were derived from quaternary hydrotalcite. • Mn dopants regulated the interaction between Ni and Mg(Mn)AlOx, increasing the surface Ni0/Ni2+ ratio. • The doubled TOF was correlated to the tailored surface Ni0 species and medium-strength basic sites. [ABSTRACT FROM AUTHOR]

Exploiting Ni-based catalysts with excellent low-temperature activity is significant for CO 2 methanation, which is a promising route to CO 2 utilization. In this work, a facile combustion-impregnation method was developed to prepare the SiO 2 supported Ni catalysts. Small Ni particles (around 6 nm) and massive Ni–SiO 2 interface could be obtained due to the "combustion" process. The H 2 -temperature programmed desorption (H 2 -TPD) revealed the existence of Ni–SiO 2 interface and confirmed the high Ni dispersion obtained by this method, which were vital for the activation of reactant. Moreover, more medium basic sites which were beneficial for the CO 2 activation could also be created. In comparison with the reference Ni/SiO 2 catalyst prepared by the conventional impregnation method, much higher CO 2 conversion (66.9%) and more superior selectivity to CH 4 (94.1%) were achieved with the Ni/SiO 2 -Gly catalyst at 350 °C. Additionally, it was also found that glucose, citric acid and glycine were all effective fuels for this combustion-impregnation method, and the as-prepared catalysts all exhibited greatly improved low-temperature activity. Therefore, this work represents an important step toward developing Ni-based catalysts for CO 2 methanation by a promising wide-used method. [Display omitted] • A novel combustion-impregnation method is developed to prepare Ni-based catalysts. • High Ni dispersion and massive Ni–SiO 2 interface are obtained by this novel method. • An improved low-temperature activity with high CH 4 selectivity can be obtained. • Glucose, citric acid and glycine are all effective for the "combustion" process. [ABSTRACT FROM AUTHOR]

In this work, single-atom Ag anchored on nitrogen-doped carbon catalysts are designed to investigate the effect of different N -coordination environments on the ECO 2 RR products pathway. The combination of experiments and theory calculations reveal that the Ag-N 4 -C (pyrrolic N) site facilitates the adsorption of CO 2 to produce CO, whereas Ag-N 3 -C (pyridine N) exhibits the highest binding energy (-4.73 eV) to hold *CO intermediates for dimerization, consequently steering the pathway to ethanol (C 2 H 5 OH) formation with a FE of 42% at −0.97 V vs. RHE. [Display omitted] • Ag N C catalysts with controllable N species and content were prepared. • ECO 2 RR products from CO to C 2 H 5 OH can be regulated. • Ag-N-rGO 0.025 M with pyrrolic N promotes the production of CO. • Ag-N-C 0.05 M with pyridine N facilitates a FE C2H5OH of 42 % at −0.97 V RHE. • Experiments and DFT calculations reveal the structure–activity relationship. The rational modulation of the coordination environment of the active center of single-atom catalysts (SACs) is a potential strategy to improve the activity and selectivity of electrocatalytic CO 2 reduction. We developed a series of single-atom Ag-anchored on N -doped carbon catalysts with different N -coordination environments by regulating the carbon source (glucose/graphene oxide, GO). Results demonstrated that the CO 2 -to-CO/C 2 H 5 OH pathway can be converted through reasonable regulation of the content of pyrrolic N and pyridine N. At a highly dominant pyrrolic N content of 40.0 %, the electrocatalyst of Ag-N-rGO 0.025 M facilitates the formation of CO with a Faradaic efficiency (FE) of 69.7 %. By contrast, when the pyridine N content is 70.5 %, the best Ag-N-C 0.05 M catalyst in the H-cell shows an FE of 42 % for C 2 H 5 OH at −0.97 V vs. RHE; moreover, the FE is stable at 40 % within 31 h. Density functional theory calculations further confirm that the pyrrolic N site is conducive to the conversion of CO 2 to intermediate *CO, whereas pyridine N exhibits the highest binding energy (ΔG = -4.73 eV) to hold *CO intermediates for dimerization, consequently steering the pathway to the formation of C 2 H 5 OH. The results of this study provide novel insights into the rational design of carbon-based SACs based on efficient electrochemical CO 2 reduction reaction and the regulation of CO 2 selectivity and activity for C 2 H 5 OH production. [ABSTRACT FROM AUTHOR]

[Display omitted] • The new NiMgAl-LDO catalysts were synthesized via sequenced precipitation for CO 2 -to-SNG process. • The optimized Ni-LDO-A70 catalyst gave 7 times higher value of per mole nickel activity than that of traditional sample (Ni-LDO-A0) at 573 K. • Ni particle size had been tuned by sequenced precipitation, evidenced by characterizations. • The ratio increasement of medium-strong basic sites and the promoted nickel reducibility were observed. In this work, hydrotalcite-derived new Ni-LDO catalysts were synthesized via sequenced precipitation, for CO 2 catalytic reduction to synthetic natural gas (SNG) with high performances, while the traditional sample via coprecipitation was prepared and measured as the comparison. By regulating precipitation procedure, a significant performance enhancement was attained, in which the CO 2 conversion rate per gram nickel was 7-times higher than that of the conventional comparison, at the temperature of 573 K and atmospheric pressure. In addition, the desired product selectivity is up to 99%. Structural characterizations proved that the as-synthesized catalysts showed layered meso -porous properties. An increasing Ni particle size and higher coverage of medium-strong basic sites was observed over the optimized catalyst sample prepared when part of Mg2+ and Al3+ were precipitated at first step. Catalyst surface nickel enrichment and promoted reducibility were also achieved when using sequenced precipitation. This work achievements provided a new route for surface nickel enrichment of much more active hydrotalcite-derived Ni-LDO layered catalysts for enhanced performances. [ABSTRACT FROM AUTHOR]

Note: The source of the background picture is from website. [Display omitted] • K 3 PO 4 could adjust Cu+/(Cu0 + Cu+) and promote catalytic performance greatly. • By regression analysis, Fe2+, Cu0, and medium base site show linear relation to C 2+ OH STY. • Significance level of above three factors follows Cu0＞Fe2+＞medium base sequence. • Conversion of Fe0 to Fe 3 C or Fe 3 O 4 leads to activity decrease. CO 2 hydrogenation to C 2+ OH is an effective way to diminish CO 2 emissions. Although challenges still exist in large-scale applications, CuFeZn catalysts attract extensive attention due to their low-cost. Herein, CuFeZn catalysts are modified by different amounts of K 3 PO 4 , (KP) 0.1 CuFeZn exhibits an excellent catalytic performance (total alcohols selectivity of 15.76 % at CO 2 conversion of 38.10 %, C 2+ OH/ROH fraction of 94.23 %, and C 2+ alcohols space–time-yield (STY) of 53.81 mg·mL−1·h−1). Combined with a series of characterization results, it is found that the effect of K 3 PO 4 is complex, and the proportion of Fe2+, Cu0 and medium base shows perfect linear relation to STY of C 2+ OH. The significance level of the above three factors is in the following sequence: Cu0＞Fe2+＞medium base. The introduction of K 3 PO 4 decreases the proportion of Fe2+ (active site for RWGS, the competitive reaction for C–C coupling) and increases the proportion of Cu+/(Cu++Cu0) (Cu+ is the active site for C–C coupling) due to the synergistic effect of Cu0 and Cu+, thereby improving the synthesis of C 2+ OH. Moreover, conversion of Fe0 to Fe 3 C or Fe 3 O 4 plays negative roles in the stability of the catalysts. [ABSTRACT FROM AUTHOR]