Alumina-promoted mesoporous sulfated zirconia: A catalyst for n-butane isomerization

Mesoporous sulfated zirconia (MP-ZrO₂) were synthesized hydrothermally using Zr(O-nPr)₄ as zirconium precursor, ammonium sulfate as sulfur source and CTABr as template. Then the as-synthesized mesoporous materials were directly impregnated with aluminum sulfate to give the acidic Al-promoted mesoporous sulfated zirconia. (AS/MP-ZrO₂). The AS/MP-ZrO₂ catalyst was characterized by nitrogen physisorption (BET) for texture properties, by X-ray diffraction (XRD) for confirming the phase and by TEM for particle sizes. The catalytic conversion of n-butane isomerization was measured in a flow reactor. With the addition of a proper amount of aluminum as a promoter, the catalytic behavior for n-butane isomerization at low temperature in flow system was strongly promoted. The increase of activity was determined primarily by the amount of alumina addition and by the temperature of calcination. The highest catalytic performance is for the catalyst prepared at an optimum 3 mol.% Al loading and calcination at 650°C. The nature of the acidic sites was determined by X-ray photoelectron spectroscopy (XPS) measurements of N 1 s of the adsorbed pyridine. Three kinds of acid sites were identified on the catalyst: a Lewis site, a weak Brønsted site and a strong Brønsted site. The catalytic activities are correlated with the amount of weak Brønsted acid sites. The remarkable activity and stability of the Al-promoted catalysts are due to a balanced distribution of acid sites strength with an enhanced amount of weak Brønsted acid sites.