The Catalyst Review December 2020 - 15

EXPERIMENTAL
Recent Progress in CO Hydrogenation over Bimetallic Catalysts for Higher Alcohol Synthesis...
Hydrogenation of carbon monoxide (CO) is typically carried out using different
processes such as Fischer-Tropsch (FT) synthesis, methanol synthesis, and higher
alcohol synthesis. In recent years, researchers have focused on CO hydrogenation
(FT) over bimetallic catalysts to produce C1-C4 alcohols. These products can be used
directly as fuels or octane-enhancing fuel additives or can be converted to other
useful products such as ethers. To date, such efforts have proven to be ineffective
because of low alcohol selectivity and poor catalyst stability. Herein, this mini
review's authors discuss the hydrogenation of carbon monoxide over bimetallic
catalysts for higher alcohol synthesis. Recent progress in developing active
bimetallic centers and their roles in the reaction mechanism during higher alcohol
synthesis are presented.

Table 1. Summary of catalysts used for carbon
monoxide hydrogenation to higher alcohol.

The authors begin with a review of recent trends involving alkali-modified
methanol catalysts, copper-based FT catalysts, rhodium (Rh)-based catalysts, and
molybdenum (Mo)-based catalysts (Table 1). Among these catalysts, copper-based
catalysts have been reported to be the most effective for higher alcohol synthesis.
Reviews of performance factors such as metal type, support type, support
treatment, and the effects of promoters and preparation methods are presented in
summary form.
The authors then discuss current mechanistic studies involving copper-based
bimetallic catalysts, coupled with iron or cobalt for higher alcohol synthesis. The
mechanism of CO insertion over copper-based FT catalysts is shown in Scheme
1. Recent studies indicate that a CO insertion mechanism seems to be a typical
process. Additional studies involving copper, iron, and cobalt-based bimetallic
catalysts indicate that the copper-FT element center serves as the active dualsite for the higher alcohol synthesis and that iron and cobalt facilitates carbon
chain growth through methylene formation. Methylene formation arises from CO
dissociation and hydrogenation over the iron and the cobalt, leading to surface
alkyl groups' formation. On the other hand, chain oxygenation occurs via nondissociative CO adsorption over copper.

Scheme 1. Mechanism of CO insertion over modified
FT catalysts.

Additional studies focusing on the adsorption of CO over copper- and cobalt-based
mono- and bimetallic catalysts using infrared spectroscopy diagnostics have shown
that a new dual-site in the form of a metallic oxide cobalt pair is formed. Metallic
cobalt was found to be the active site on the bimetallic CuCo/SiO2 catalyst, while
a cobalt pair comprising Co0 and Coδ+ was the active site on the Co/SiO2 catalyst. It
was noted that under certain conditions, only cobalt could lead to higher alcohol
synthesis through the formation of a metal oxide pair. Moreover, strong metalsupport interaction and high cobalt dispersion promoted Coδ+ surface concentration
suggesting that the metal oxide pair's concentration may also play a dual-site role
for higher alcohol synthesis depending upon process conditions. Source: Khan WU,
Baharudin L, Choi J, et al. (2020). ChemCatChem, doi.org/10.1002/cctc.202001436.
Cobalt@Cucurbit[5]uril Complex as Highly Efficient Supramolecular Catalyst for Electrochemical
and Photoelectrochemical Water Splitting...
The use of catalytic water oxidation as a source of protons for hydrogen production has long proven to be one of the major obstacles
for overall water splitting. However, it has been suggested that the integration of semiconductors with water oxidation catalysts may
prove a viable solution due to their low catalytic activity towards the oxygen evolution reaction (OER).
Cucurbiturils (CB[n]) are macrocyclic host compounds that can readily coordinate with metal cations because of carbonyl
groups directed towards their cyclic structure's cavity. Herein, the authors used a relatively water-soluble member of this class
of compounds, CB[5], in combination with Co2+ cation to form a supramolecular assembly. This assembly was then deposited
on both porous indium tin oxide(ITO) and porous BiVO4 substrates (Scheme 1) to evaluate their electrochemical-driven and
The Catalyst Review

December 2020 15

https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202001436

The Catalyst Review December 2020

Table of Contents for the Digital Edition of The Catalyst Review December 2020