研究鋁活化不同形貌的硫酸鋯觸媒之催化活性及酸性鑑定

Abstract

研究鋁活化不同形貌的硫酸鋯觸媒之催化活性及酸性鑑定

Promotion of sulfated zirconia with alumina improved the efficiency and stability of sulfated zirconia catalysts in n-butane isomerization, with a more substantial effect when the promoter was introduced via impregnation on as-synthesized MCM-41, zirconia nanoparticles, and mesoporous sulfated zirconia.

The addition of small amount of alumina dramatically enhances the catalytic activity for n-butane conversion. The increase of activity was determined primarily by the amount of aluminum addition and the temperature of calcination. The reasons are several: first, nano-size carriers can help better the dispersion of sulfated tetragonal ZrO2. Secondly, the addition of Al can prevent the transformation of tetragonal sulfated zirconia into monoclinic sulfated zirconia. Thirdly, according to the results of catalytic activities and characterization of acid sites, the remarkable activity and stability of the Al-promoted catalysts are due to a different distribution of acid sites strength and to an enhanced amount of weak Brønsted (II) acid sites with intermediate strength on the optimal catalysts.

According to the mechanisms of n-butane isomerization, product distribution is related to the reaction path. The overall reaction mechanism of the isomerization of n-butane over sulfated zirconia was considered and demonstrated three assumptions: (1) The bimolecular mechanism is the major pathway over the “Brønsted (I)” acid sites in the initial period. (2) The “Brønsted (II)” acid sites play an important role via unimolecular mechanism to maintain the steady conversion in the subsequent period. (3) Furthermore, the contribution of Lewis acid sites is negligible.