The use of methanol as a fuel and chemical feedstock could become very important in the development of a more sustainable society if methanol could be efficiently obtained from the direct reduction of CO2 using solar-generated hydrogen. If hydrogen production is to be decentralized, small-scale CO2 reduction devices are required that operate at low pressures. Here, we report the discovery of a Ni-Ga catalyst that reduces CO2 to methanol at ambient pressure. The catalyst was identified through a descriptor-based analysis of the process and the use of computational methods to identify Ni-Ga intermetallic compounds as stable candidates with good activity. We synthesized and tested a series of catalysts and found that Ni5Ga3 is particularly active and selective. Comparison with conventional Cu/ZnO/Al2O3 catalysts revealed the same or better methanol synthesis activity, as well as considerably lower production of CO. We suggest that this is a first step towards the development of small-scale low-pressure devices for CO2 reduction to methanol.
A nanodispersed
intermetallic GaPd2/SiO2 catalyst
is prepared by simple impregnation of industrially relevant high-surface-area
SiO2 with Pd and Ga nitrates, followed by drying, calcination,
and reduction in hydrogen. The catalyst is tested for CO2 hydrogenation to methanol at ambient pressure, revealing that the
intrinsic activity of the GaPd2/SiO2 is higher
than that of the conventional Cu/ZnO/Al2O3,
while the production of the undesired CO is lower. A combination of
complementary in situ and ex situ techniques are used to investigate
the GaPd2/SiO2 catalyst. In situ X-ray diffraction
and in situ extended X-ray absorption fine structure spectroscopy
show that the GaPd2 intermetallic phase is formed upon
activation of the catalyst via reduction and remains stable during
CO2 hydrogenation. Identical location–transmission
electron microscopy images acquired ex situ (i.e., micrographs of
exactly the same catalyst area recorded at the different steps of
activation and reaction procedure) show that nanoparticle size and
dispersion are defined upon calcination with no significant changes
observed after reduction and methanol synthesis. Similar conclusions
can be drawn from electron diffraction patterns and images acquired
using environmental TEM (ETEM), indicating that ETEM results are representative
for the catalyst treated at ambient pressure. The chemical composition
and the crystalline structure of the nanoparticles are identified
by scanning TEM energy dispersive X-ray spectroscopy, selected area
electron diffraction, and atomically resolved TEM images.
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