Influence of the calcination temperature on the acidic and catalytic properties of sulphated zirconia

• Published in: Applied catalysis. A, General Vol. 171; no. 2; pp. 207 - 217
• Main Authors: Tran, M.-Trung, Gnep, N.S., Szabo, G., Guisnet, M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 13-07-1998; Elsevier
• Subjects: Acidity; Calcination temperature; Catalysis; Catalysts: preparations and properties; Chemistry; Deactivation; Exact sciences and technology; General and physical chemistry; Propane and n-butane transformations; Reaction mechanism; Sulphated zirconia; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Sulphated zirconia; Reaction mechanism; Acidity; Propane and n-butane transformations; Deactivation; Calcination temperature; Lewis acid; Stability; Hydrocarbon; Catalyst selectivity; Experimental study; Calcining; Infrared spectrometry; Zirconia; Butane; Heterogeneous catalysis; Brönsted acid; Catalyst activity; Catalyst; Propane
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/S0926-860X(98)00099-4

The effect of the calcination temperature (
T
c from 500 to 700°C) of sulphated zirconia on acidic and catalytic properties was investigated. The sulphur content decreases from 2.5 to 1
wt% when
T
c increases from 500 to 700°C; the BET surface area is between 90 and 100
m
2
g
−1 for all the samples with the exception of that calcined at 700°C (80
m
2
g
−1). IR spectroscopy has been used to characterize the hydroxyl groups and to determine the concentration of Brönsted- and Lewis-acid sites from pyridine adsorption. The activities, stabilities and selectivities of the sulphated zirconia samples were compared for both
n-butane and propane transformations at 250°C. For
T
c≤600°C, the concentrations of Lewis- and Brönsted-acid sites are practically identical. For higher calcination temperatures, the Lewis acidity increases at the expense of the Brönsted acidity. The increase with
T
c in the wave number of the hydroxyl band, the decrease of the ratio between the number of protonic sites retaining pyridine adsorbed at 450 and 150°C as well as the increase in the ratio of
n-butane and propane reactivities suggest that the acid strength decreases when
T
c increases. In agreement with this proposal and with the decrease in the number of protonic sites, there is a decrease in activity when
T
c increases from 600 to 700°C. However, the reverse is found for lower calcination temperatures. The unexpected low activity of the samples calcined at lower temperatures may be due to their very fast initial deactivation (before the first activity measurement). Deactivation is mainly due to poisoning of the acid sites by carbonaceous deposits. However, sulphur elimination with protonic sites consumption also plays a limited role.