Jc. Vartuli et al., Characterization of the acid properties of tungsten/zirconia catalysts using adsorption microcalorimetry and n-pentane isomerization activity, J CATALYSIS, 187(1), 1999, pp. 131-138
Ammonia adsorption microcalorimetry was conducted on various solid acid tun
gsten/zirconia catalysts prepared by different techniques. The calorimetric
data were compared to catalytic test results using n-pentane isomerization
as a measure of acid activity. The results show that (1) the co-precipitat
ion method of making the tungsten/zirconia catalyst produces a greater numb
er of acidic sites than impregnating tungsten on hydrous zirconia, resultin
g in a more active catalyst, and (2) the addition of small amounts of iron
to the tungsten/zirconia catalyst increases the acid site strength as deter
mined by ammonia adsorption and improves the paraffin isomerization activit
y. The calorimetry data indicate that the acid site strength of the tungste
n/zirconia materials is similar to or slightly higher than that found in ze
olites or sulfated zirconia and is comparable to sulfuric acid. However, th
e paraffin isomerization activity results suggest that the acid sites of th
e tungsten/zirconia catalyst should be about four orders of magnitude more
active than that of zeolite beta on the basis of turnover frequency. Our ex
perimental results indicate a lack of correlation between the heat of ammon
ia adsorption with catalytic activity. Comparisons of catalytic activity be
tween materials based entirely on acid strength may not be valid, and kinet
ic probes would be more appropriate. (C) 1999 Academic Press.