Dr. Brown et Aj. Groszek, Heats of adsorption of ammonia on a zeolite catalyst and an acid-activatedclay catalyst determined by flow adsorption microcalorimetry, LANGMUIR, 16(9), 2000, pp. 4207-4212
Measurements of heats of adsorption of ammonia from a nitrogen carrier have
been carried out on zeolite Y and K10 clay catalysts in the acid and Na+ f
orms. The equipment used was a new model of the Microscal flow calorimeter
(FMC) linked to a thermal conductivity detector in which the rates of adsor
ption and desorption and the associated rates of heat evolution or absorpti
on were measured simultaneously at atmospheric pressure and temperatures ra
nging from 150 to 207 degrees C. Ammonia was used as a probe interacting wi
th the acid sites on the catalysts. The work revealed new information in su
rface heterogeneity of the catalysts existing under flow conditions at atmo
spheric pressure of a nitrogen carrier. It was found that the irreversibly
adsorbed ammonia is mobile on both catalysts. Molar heats of adsorption rec
orded as surface coverage is increased show that the sites covered first ar
e not necessarily those with the highest heats of adsorption, illustrating
that this flow technique gives important information on the relative access
ibilities of acid sites as well as their strengths.