Seite - 124 - in Advanced Chemical Kinetics

The concentrationsCiwere allocated as follows: C1 = glycerol; C2 = glyceric acid (GA); C3 = FOP* (further oxidationproducts—FOP—were lumped together as tartronic acid, oxalic acid, glycolic acid and formic acid); C4 = LACandC5 = acetic acid. The reason FOPwere lumped together is that the studywasonlyconcernedwith theapparent competitionbetween the rate of formationofLACand that ofGAfromglycerol and thepossible effect of Lewis acidityon the rate of LAC formation. Generally, there was a good fit between the fitted pseudo-zero- ordermodelandexperiment forboth testedcatalysts.The resultsof the regressionanalysesof themodel against experimental data showedagood fit as visually seen inFigure 8; the rate constantsaresummarisedinTable2 forbothAu/γ-Al2O3andAu-MoO3/γ-Al2O3, respectively. Theestimatedkineticparameterswerestatistically significant. FromTable2,oneof themost intriguingresultswasthe ‘jump’ in therateof formationofLAC (k4) over theAu-MoO3/γ-Al2O3 catalyst relative toAu/γ-Al2O3. IndeedEq. (10),which com- pares the rate of formation of LAC over the two catalysts, paints a clearer picture. It is conceivable that the extra Lewis acidity provided by Mo played a role in the promoted Figure 7. Reactionnetworkused for the kineticmodelling of the glycerol oxidation. FOP* = further oxidationproducts (tartronic, oxalic,glycolicand formicacids). Figure 8. Comparison of computed and experimental data for glycerol oxidation assuming zero-order kinetics over Au-MoO3/γ-Al2O3 (top)andAu/γ-Al2O3 (bottom);Glycerol ( ), glycericacid ( ), FOP* ( ),LAC( ), aceticacid ( ). Advanced Chemical Kinetics124