Seite - 120 - in Advanced Chemical Kinetics

The rate constants, k, were estimated bynon-linear regression of themodel shown inEq. (2) against experimental data and the results summarised inTable 1, showing the apparentEA determined fromtheestimatedrate constantsusinga two-pointArrheniusequation, thus: EA¼T1�T2�RT2�T2 ln k2 k1 (3) By the use of a two-pointArrhenius equationwith catalyst activity beingmeasured at 60 and 90�C, thepre-exponential factor,A,wasdetermined tobeequal to274695moldm�3h�1under the reactionconditionsemployed. Inaddition, the kvalues for thevarious catalystsweredeter- mined experimentally using Eq. (2). Then, since k¼274695:e�EA=RT, and in substituting the values forAand k in theArrheniusequation, theEAper catalystwere found tobe inveryclose proximity, with the least active catalyst (Au/γ-Al2O3) having the highest EA = 37.4 kJ mol �1, followedbytheAu-MoO3/γ-Al2O3withEA=35.4kJmol �1.Therateconstants (k)of thecatalysts for overall glycerol conversion, calculated from experimental resultswere observed to be 2.22 and1.14mol dm� 3 h� 1 for theAu-MoO3/γ-Al2O3 andAu/γ-Al2O3, respectively, per gramof catalyst.Alternatively,whennormalised to the amount ofAu in the catalyst, the rate constants werefoundtobe642moldm�3h�1 g�1Au forAu-MoO3/γ-Al2O3catalystand252moldm �3 h�1 g�1Au forAu/γ-Al2O3catalyst. Figure4. Conversionofglycerolover timeby0.9-wt%Au/γ-Al2O3 (106�150mμ) catalyst; 1000 rpm,NaOH/glycerol=2:1, at60and90�C,underanO2pressureof8.5bar. Advanced Chemical Kinetics120