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Abstract:
Research on biomass derived raw materials for conventional catalytic processes, especially those directed to replace human dependence on fossil-based energy, is a high priority academic topic worldwide. Glycerol, the ubiquitous by-product of biodiesel manufacture, is seen as a promising building block due to its versatile functionality. Hence, research efforts to valorize it by selective partial oxidation are widespread. Fundamental knowledge of the interaction of glycerol with metal surfaces in the presence of oxygen is of extreme importance to rationally design new catalytic materials. In this work, a complete study of glycerol interaction with pristine and oxygen modified Au(111) surfaces is presented, by means of X-ray photoelectron and infrared reflection absorption spectroscopies, aided by temperature programmed desorption (TPD) experiments using mass spectrometry. On the clean Au(111) surface, glycerol adsorbs at 150 K through weak interactions between the oxygen atoms from OH groups and gold atoms. No thermal activation is observed and only molecular desorption is detected in TPD at 293 K. On the other hand, when the Au surface is precovered with oxygen atoms in the form of chemisorbed oxygen, glycerol adsorbs in a slightly different geometry and is activated even at low temperatures. The observation of spectral features related to C=O bonds clearly corroborates the activation of the alcohol groups toward partial oxidation intermediates. Possible products desorbing from the surface due to this activation are identified as dihydroxyacetone, hydroxypiruvic, tartronic and formic acid, as well as H2O and CO2.
