Page - 113 - in Advanced Chemical Kinetics

Chapter 7 Oxidation of Glycerol to Lactic Acid by Gold on Acidified Alumina: A Kinetic and DFT Case Study Thabang A. Ntho, Pumeza Gqogqa and James L. Aluha Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.70485 Provisionalchapter Oxi ationofGlycerol toLacticAcidbyGoldonAcidified Alumina:AKineticandDFTCaseStudy ThabangA.Ntho,PumezaGqogqaand JamesL.Aluha Additional information isavailableat theendof thechapter Abstract The aim of this chapter is to present proposed kinetic and density functional theory (DFT)models for the selective oxidation of glycerol to various hydroxy-acids over an acidified Au/γ-Al2O3 catalyst. Glycerol oxidation over gold-based catalysts to value- added chemicals continues to attract attentionworldwide. Both the kinetics and theo- reticalmechanismsof thisreactionhavebeenreportedinthepast.However,someof the reportedkineticdatawaspossiblycollectedundermass transfer limitations. In this case studywedemonstrate that ifmasstransfer iseliminated,apseudozero-ordermodelcan be fitted to the experimental datawith a high degree of correlation. Furthermore, we propose a plausible mechanism of pyruvaldehyde (PA) isomerisation to lactic acid (LAC)over supportedmolybdenumLewis acid sites as investigatedwithdensity func- tional theory (DFT) approach.AproposedDFTmodel suggested that the rate-limiting step in the isomerisationofPAtoLAC, catalysedbyaMoLewis acid-site, couldbe the dissociationofaproton fromanadsorbedwatermolecule– theprotonationstep. Keywords:gold, catalyst, alumina, support-acidity,glycerol-oxidation, lacticacid, kinetics,DFT 1. Introduction Lactic acid (LAC), asnotedbyWeeetal. [1], is oneof themostvaluable chemicals in industry todayandiswidelyusedinthefood,cosmetic,pharmaceutical,andchemical industries. Inthe food industry, for example, itmaybeused as a preservative, an acidulant, or for flavouring, while in the textile, pharmaceutical andchemical industry it is usedas a rawmaterial for the production of lactate ester, propylene glycol, 2,3-pentanedione, propanoic acid, acrylic acid, © TheAuthor(s). Licensee InTech.This chapter isdistributedunder thetermsof theCreativeCommons AttributionLicense (http://creativecommons.org/licenses/by/3.0),whichpermitsunrestricteduse, distribution, andeproduction inanymedium,providedtheoriginalwork isproperlycited. DOI:10.5772/intechopen.70485 © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.