Functional Materials for Energy

Structure-dependent Properties Guide Catalyst Design for Oxygenates Conversion

The product selectivity at 200 °C for CeO2 nanoshapes upon acetaldehyde reaction.

The catalytic transformation of oxygenates (i.e. aldehydes, alcohols, ketones) on metal oxides to generate value added products such as fuels and additives is of great importance industrially, yet is not well-understood.  ORNL researchers have provided new insights into how oxygenates react on metal oxide particles with well-defined structures.  Shape-controlled cerium oxide (CeO2) nanocubes with {100} facets, nanowires with a highly defective surface, and nano-octahedra with {111} facets were used to evaluate the structure-dependent properties for the adsorption and reaction of acetaldehyde, a model oxygenate.  Temperature-programmed desorption, isothermal measurements, and in situ infrared spectroscopy were used to monitor the adsorption and catalytic reactions of acetaldehyde on CeO2 nanoshapes.  It was shown that all the nanoshapes produced the coupling product, crotonaldehyde, via an Aldol condensation reaction.  However, the wires and cubes additionally produced large amounts of ethanol (see image) via a Cannizzaro disproportionation reaction in which the first step involves the attack of the acyl carbon of acetaldehyde by a basic surface CeO2 oxygen atom.  This difference in reactivity between the cubes and wires versus the octahedra is attributed to the {100} and defective surfaces possessing more basic surface oxygen atoms than the {111} surface.  In addition, the amount of defects on the various surfaces, vacancy formation energies, and surface energies contributed to variations in the reactivity of the CeO2 nanoshapes.  The evaluation of the influence of various shape-dependent properties on catalytic reaction of oxygenates provides fundamental understanding that can guide the design of more active and selective catalysts to generate value-added products from oxygenates.

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Mann, A.K.P., Wu, Z., Calaza, F.C., Overbury, S.H., ACS Catal., 2014, 4, 2437. DOI: 10.1021/cs500611g


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