CoFe alloy carbide catalysts for higher alcohols synthesis from syngas: Evolution of active sites and Na promoting effect

Low-temperature CO2 Hydrogenation to Olefins on Anorthic NaCoFe Alloy Carbides

The hydrogenation of carbon dioxide to olefins (CTO) represents an ideal pathway towards carbon neutrality. However, most current CTO catalysts require a high-temperature condition of 300-450 °C, resulting in high energy consumption and possible aggregation among active sites. Herein, we developed an efficient iron-based catalyst modified with high-sodium content (7 %) and low-cobalt content (2 %), achieving a CO2 conversion of 22.0 % and an olefin selectivity of 55.9 % at 240 °C and 1000 mL/g/h, and it is even active at 180 °C and 4000 mL/g/h with more than 25 % olefins in hydrocarbons. The catalyst was kept stable under continuous operating conditions of 500 hours. Numerous characterizations and calculations reveal high content of sodium as an electronic promoter enhances the stability of the active anorthic Fe5C2 phase at low temperatures. Further incorporating the above catalyst with cobalt, as a structural promoter, causes Fe species to form a FexCoy alloying phase, which in turn facilitates the formation of higher active anorthic (FexCoy)5C2 phase, different from the conventional carbides and alloy carbides. An in-depth investigation of the synergistic effects of structural and electronic promoters can improve catalyst performance, increase reaction efficiency and cost-effectiveness, and provide profound insights for understanding and optimizing CO2 hydrogenation reactions.

Atomically intimate assembly of dual metal-oxide interfaces for tandem conversion of syngas to ethanol

Selective conversion of syngas to value-added higher alcohols (containing two or more carbon atoms), particularly to a specific alcohol, is of great interest but remains challenging. Here we show that atomically intimate assembly of FeOx-Rh-ZrO2 dual interfaces by selectively architecting highly dispersed FeOx on ultrafine raft-like Rh clusters supported on tetragonal zirconia enables highly efficient tandem conversion of syngas to ethanol. The ethanol selectivity in oxygenates reached ~90% at CO conversion up to 51%, along with a markedly high space-time yield of ethanol of 668.2 mg gcat-1 h-1. In situ spectroscopic characterization and theoretical calculations reveal that Rh-ZrO2 interface promotes dissociative CO activation into CHx through a formate pathway, while the adjacent Rh-FeOx interface accelerates subsequent C-C coupling via nondissociative CO insertion. Consequently, these dual interfaces in atomic-scale proximity with complementary functionalities synergistically boost the exclusive formation of ethanol with exceptional productivity in a tandem manner.

Carbon-Supported Fe-Based Catalyst for Thermal-Catalytic CO2 Hydrogenation into C2+ Alcohols: The Effect of Carbon Support Porosity on Catalytic Performance

Carbon materials supported Fe-based catalysts possess great potential for the thermal-catalytic hydrogenation of CO2 into valuable chemicals, such as alkenes and oxygenates, due to the excellent active sites' accessibility, appropriate interaction between the active site and carbon support, as well as the excellent capacities in C-O bond activation and C-C bond coupling. Even though tremendous progress has been made to boost the CO2 hydrogenation performance of carbon-supported Fe-based catalysts, e.g., additives modification, the choice of different carbon materials (graphene or carbon nanotubes), electronic property tailoring, etc., the effect of carbon support porosity on the evolution of Fe-based active sites and the corresponding catalytic performance has been rarely investigated. Herein, a series of porous carbon samples with different porosities are obtained by the K2CO3 activation of petroleum pitch under different temperatures. Fe-based active sites and the alkali promoter Na are anchored on the porous carbon to study the effect of carbon support porosity on the physicochemical properties of Fe-based active sites and CO2 hydrogenation performance. Multiple characterizations clarify that the bigger meso/macro-pores in the carbon support are beneficial for the formation of the Fe5C2 crystal phase for C-C bond coupling, therefore boosting the synthesis of C2+ chemicals, especially C2+ alcohols (C2+OH), while the limited micro-pores are unfavorable for C2+ chemicals synthesis owing to the sluggish crystal phase evolution and reactants' inaccessibility. We wish our work could enrich the horizon for the rational design of highly efficient carbon-supported Fe-based catalysts.

Tailoring the CO2 Hydrogenation Performance of Fe-Based Catalyst via Unique Confinement Effect of the Carbon Shell

Even though Fe-based catalysts have been widely employed for CO2 hydrogenation into hydrocarbons, oxygenates, liquid fuels, etc., the precise regulation of their physicochemical properties is needed to enhance the catalytic performance. Herein, under the guidance of the traditional concept in heterogeneous catalysis-confinement effect, a core-shell structured catalyst Na-Fe3 O4 @C is constructed to boost the CO2 hydrogenation performance. Benefiting from the carbon-chain growth limitation, tailorable H2 /CO2 ratio on the catalytic interface, and unique electronic property that all endowed by the confinement effect, the selectivity and space-time yield of light olefins (C2 = -C4 = ) are as high as 47.4 % and 15.9 g molFe -1  h-1 , respectively, which are all notably higher than that from the shell-less counterpart. The function mechanism of the confinement effect in Fe-based catalysts are clarified in detail by multiple characterization and density functional theory (DFT). This work may offer a new prospect for the rational design of CO2 hydrogenation catalyst.

In-Situ-Formed Potassium-Modified Nickel-Zinc Carbide Boosts Production of Higher Alcohols beyond CH4 in CO2 Hydrogenation

Ni-based catalysts have been widely studied in the hydrogenation of CO2 to CH4 , but selective and efficient synthesis of higher alcohols (C2+ OH) from CO2 hydrogenation over Ni-based catalyst is still challenging due to successive hydrogenation of C1 intermediates leading to methanation. Herein, we report an unprecedented synthesis of C2+ OH from CO2 hydrogenation over K-modified Ni-Zn bimetal catalyst with promising activity and selectivity. Systematic experiments (including XRD, in situ spectroscopic characterization) and computational studies reveal the in situ generation of an active K-modified Ni-Zn carbide (K-Ni3 Zn1 C0.7 ) by carburization of Zn-incorporated Ni0 , which can significantly enhance CO2 adsorption and the surface coverage of alkyl intermediates, and boost the C-C coupling to C2+ OH rather than conventional CH4 . This work opens a new catalytic avenue toward CO2 hydrogenation to C2+ OH, and also provides an insightful example for the rational design of selective and efficient Ni-based catalysts for CO2 hydrogenation to multiple carbon products.

Chemocatalytic Conversion of Lignocellulosic Biomass to Ethanol: A Mini-Review

Ethanol has been widely used as a clean fuel, solvent, and hydrogen carrier. Currently, ethanol is generally produced through fermentation of starch- and sugarcane-derived sugars (e.g., glucose and sucrose) or ethylene hydration. Its production from abundant and inexpensive lignocellulosic biomass would facilitate the development of green and sustainable society. Biomass-derived carbohydrates and syngas can serve as important feedstocks for ethanol synthesis via biological and chemical pathways. Nevertheless, the biological pathway for producing ethanol through biomass-derived glucose fermentation has the disadvantages of long production period and carbon loss. These issues can be effectively mitigated by chemocatalytic methods, which can readily convert biomass to ethanol in high yields and high atomic efficiency. In this article, we review the recent advances in chemocatalytic conversion of lignocellulosic biomass to ethanol, with a focus on analyzing the mechanism of chemocatalytic pathways and discussing the issues related to these methods. We hope this mini-review can provide new insights into the development of direct ethanol synthesis from renewable lignocellulosic biomass.

Recent advances in the routes and catalysts for ethanol synthesis from syngas

Ethanol, as one of the important bulk chemicals, is widely used in modern society. It can be produced by fermentation of sugar, petroleum refining, or conversion of syngas (CO/H₂). Among these approaches, conversion of syngas to ethanol (STE) is the most environmentally friendly and economical process. Although considerable progress has been made in STE conversion, control of CO activation and C-C growth remains a great challenge. This review highlights recent advances in the routes and catalysts employed in STE technology. The catalyst designs and pathway designs are summarized and analysed for the direct and indirect STE routes, respectively. In the direct STE routes (i.e., one-step synthesis of ethanol from syngas), modified catalysts of methanol synthesis, modified catalysts of Fischer-Tropsch synthesis, Mo-based catalysts, noble metal catalysts and multifunctional catalysts are systematically reviewed based on their catalyst designs. Further, in the indirect STE routes (i.e., multi-step processes for ethanol synthesis from syngas via methanol/dimethyl ether as intermediates), carbonylation of methanol/dimethyl ether followed by hydrogenation, and coupling of methanol with CO to form dimethyl oxalate followed by hydrogenation, are outlined according to their pathway designs. The goal of this review is to provide a comprehensive perspective on STE technology and inspire the invention of new catalysts and pathway designs in the near future.