Selective Conversion of Syngas into Higher Alcohols via a Reaction-Coupling Strategy on Multifunctional Relay Catalysts

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.

Promoting nonsymmetric C-C coupling to valuable oxygenates without metal catalysts in alkali aqueous medium

Efficient conversion of C1 molecules into multicarbon oxygenates is a promising avenue for energy storage. Herein, we synthesize adjustable alkanoic acids/alcohols from formate C1 molecules via a hydrothermal reaction without any metal catalyst participation. This is achieved via HCO* and HCOO- nonsymmetric C-C coupling by alkali catalysis in aqueous medium.

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.

Selective C2+ alcohol synthesis by CO2 hydrogenation via a reaction-coupling strategy

The synergy of primary and promoting catalysts in close proximity facilitates the migration and insertion of CO*/CHxO* species, thus accelerating HA productivity over a multifunctional catalyst.

Cobalt Carbide Nanocatalysts for Efficient Syngas Conversion to Value-Added Chemicals with High Selectivity

Syngas conversion is a key platform for efficient utilization of various carbon-containing resources including coal, natural gas, biomass, organic wastes, and even CO₂. One of the most classic routes for syngas conversion is Fischer-Tropsch synthesis (FTS), which is already available for commercial application. However, it still remains a grand challenge to tune the product distribution from paraffins to value-added chemicals such as olefins and higher alcohols. Breaking the selectivity limitation of the Anderson-Schulz-Flory (ASF) distribution has been one of the hottest topics in syngas chemistry.Metallic Co⁰ is a well-known active phase for Co-catalyzed FTS, and the products are dominated by paraffins with a small amount of chemicals (i.e., olefins or alcohols). Specifically, a cobalt carbide (Co₂C) phase is typically viewed as an undesirable compound that could lead to deactivation with low activity and high methane selectivity. Although iron carbide (Fe_xC) can produce olefins with selectivity up to ∼60%, the fraction of methane is still rather high, and the required high reaction temperature (300-350 °C) typically causes coke deposition and fast deactivation. Recently, we discovered that Co₂C nanoprisms with preferentially exposed facets of (020) and (101) can effectively produce olefins from syngas conversion under mild reaction conditions with high selectivity. The methane fraction was limited within 5%, and the product distribution deviated greatly from ASF statistic law. The catalytic performances of Co₂C nanoprisms are completely different from that reported for the traditional FT process, exhibiting promising potential industrial application.This Account summarizes our progress in the development of Co₂C nanoprisms for Fischer-Tropsch synthesis to olefins (FTO) with remarkable efficiencies and stability. The underlying mechanism for the observed unique catalytic behaviors was extensively explored by combining DFT calculation, kinetic measurements, and various spectroscopic and microscopic investigation. We also emphasize the following issues: particle size effect of Co₂C, the promotional effect of alkali and Mn promoters, and the role of metal-support interaction (SMI) in fabricating supported Co₂C nanoprisms. Specially, we briefly review the synthetic methods for different Co₂C nanostructures. In addition, Co₂C can also be applied as a nondissociative adsorption center for higher alcohol synthesis (HAS) via syngas conversion. We also discuss the construction of a Co⁰/Co₂C interfacial catalyst for HAS and demonstrate how to tune the reaction network and strengthen CO nondissociative adsorption ability for efficient production of higher alcohols. We believe that the advances in the development of Co₂C nanocatalysts described here present a critic step to produce chemicals through the FTS process.

Recent advances in the direct conversion of syngas to oxygenates

Direct synthesis of oxygenates from syngas is a promising way to utilize non-petroleum carbon resources because the oxygenate products serve as precursors for the downstream production of fuels and value-added chemicals.

Novel Heterogeneous Catalysts for CO2 Hydrogenation to Liquid Fuels

Carbon dioxide (CO₂) hydrogenation to liquid fuels including gasoline, jet fuel, diesel, methanol, ethanol, and other higher alcohols via heterogeneous catalysis, using renewable energy, not only effectively alleviates environmental problems caused by massive CO₂ emissions, but also reduces our excessive dependence on fossil fuels. In this Outlook, we review the latest development in the design of novel and very promising heterogeneous catalysts for direct CO₂ hydrogenation to methanol, liquid hydrocarbons, and higher alcohols. Compared with methanol production, the synthesis of products with two or more carbons (C₂₊) faces greater challenges. Highly efficient synthesis of C₂₊ products from CO₂ hydrogenation can be achieved by a reaction coupling strategy that first converts CO₂ to carbon monoxide or methanol and then conducts a C-C coupling reaction over a bifunctional/multifunctional catalyst. Apart from the catalytic performance, unique catalyst design ideas, and structure-performance relationship, we also discuss current challenges in catalyst development and perspectives for industrial applications.

Enhanced production of C2–C4 alkanes from syngas via a metal sulfide–support interaction over Ni–MoS2/Ce1−xLaxO2−δ

The metal sulfide–support interaction and dual active sites over Ni–MoS₂/Ce_1−xLaxO_2−δ facilitated selective conversion of syngas to C2–C4 alkanes.