Development of bifunctional catalysts for the one-pot conversion of carbon dioxide to sustainable fuels

Abstract

Dimethyl ether (DME) is a non-toxic alternative fuel which can be produced via a circular carbon economy and hence can support transitioning the maritime sector towards net-zero by 2050. Conversion of CO2-to-DME can be achieved in a singular reactor using bifunctional catalysts which contain redox sites for the initial activation and hydrogenation of CO2-to-methanol, and nearby acid sites for the subsequent dehydration of this intermediate methanol-to-DME. Design of highly active, selective, and stable bifunctional catalysts requires optimisation of the two sites, and of the method used to combine these sites to yield a singular catalyst. This thesis describes the development of bifunctional catalysts for the one-pot conversion of CO2-to-DME.
Silicoaluminophosphate (SAPO) supports, e.g. SAPO-11 or SAPO-34, were particularly suited for designing bifunctional catalysts owing to their moderately acidic sites which favoured the selective dehydration of methanol-to-DME. Techniques such as impregnation and drying were used to deposit CuZnO nanoparticles (redox sites) onto the outer faces of SAPO-11/34 crystals to yield bifunctional catalysts capable of converting CO2-to-DME with high selectivity (~80%) and moderate CO2 conversions (5-8%). Proximity between the CuZnO nanoparticles and the abundant acid sites of the SAPO-11/34 support facilitated extensive dehydration of the intermediate methanol-to-DME, leading to increased localised water concentrations which supressed the parasitic CO-forming reverse water gas shift reaction. Precise control over CuZnO nanoparticle size was achieved by rationally modifying the solvent volume, drying temperature, or solvent polarity of the impregnation and drying method. In addition to the bimetallic CuZnO/SAPO bifunctional catalysts, PdZnM/SAPO-34 (where M = Cu, In, Sn, or Au) trimetallic bifunctional catalysts were also used to realise the selective conversion of CO2-to-DME with almost 40% higher activity compared to the baseline bimetallic PdZn/SAPO-34 catalyst.
The work outlined in this thesis provides valuable insights which can support the development of improved bi- and trimetallic bifunctional catalysts for the one-pot conversion of CO2-to-DME.

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Identifiers

ORCID for Maciej Grzegorz Walerowski: orcid.org/0009-0006-4763-8169

ORCID for Robert Raja: orcid.org/0000-0002-4161-7053

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