JOURNAL OF CATT.\I.YSIS 54, 365.-371 (3978) Decomposition of n-Butane on Alkaline-Earth Mordenites J. BLANCO, A. RAMOS, AND J. SORIA Instituto de Catdlisis y Petroleoquimica, Consejo Superior de Investigaciones CientiJicas, Madrid, Spain Received March 2, 1976; revised January 30, 1978 The acidity of alkaline-earth mordenites, as observed by the ir spectra of adsorbed pyridine, has been correlated with their activity as catalysts for n-butane decomposition. The results indicate that Brflnsted acid sites are the origin of the catalytic activity. However, the presence of Lewis acid sites is necessary for the reaction to take place, suggesting an inductive effect of these sites on the Brensted sites. The presence of alkaline-earth cations in decationated mor- denites decreases the activity of the original sample; this influence increases with decreasing ionic radius. This result is interpreted as a weakening of the inductive effect produced by the structural Lewis sites through a fall in their number by the cation exchange process. The re- actant molecules are coordinatively bound to the cations to an extent which is strongly de- pendent on their electrostatic field, thus influencing the accessibility of the Brensted sites. INTRODUCTION As an explanation of the acidity of cal- cium X zeolites, Hirschler (1) suggested that the cation electrostatic field tends to free a proton from a hydroxyl group attached to an adjacent silicon or aluminum atom or from a water molecule adsorbed on the cation itself. Since then, several studies have been made on the interaction between the possible catalytically active sites. Richardson (2) considered the possibility that the ionic potential of the cation results in a shift of the electron charge distribution toward the vicinity of the cation via a con- duction band model ; such an interaction would weaken the O-H bonds on the surface of the supercages and thus would modify the acidity of the hydroxyl groups. Ward (3) found that the concentration of Brqjnsted acid sites in multivalent cation zeolites appeared to be directly related to the polarizing properties of the cation. Hopkins, discussing the activity of NHa- exchanged Y zeolite (4), suggested that for cracking of n-hexane, n-heptane, and ethyl- benzene only the strongest Brgnsted sites are catalytically effective, but the presence of Lewis acid sites is either necessary or has a synergistic effect on the activity. Most of these experiments have been made with X or Y zeolites ; however, very little information is available on morden- ites, though their higher thermal stability and stronger acid sites suggest these materials as good samples for that kind of work. In a previous study on the acid sites, by ir spectroscopy using the pyridine ad- sorption method, Ramos (5) has found that, for sodium (M-Na) and decationated (M-W mordenites exchanged with alkaline-earth cations, there are variations of the pyridinium ion band with the de- gassing temperature. Some differences have also been observed in the characteristics of the Bdnsted acid sites in the series M-H-Me (Me = Ba, Ca, 36.5 0021-9517/78/0543-0365$02.00/O Copyright Q 1978 by Academic Press, Inc. All rights of reproduction in any form reserved.