鎵活化之中孔洞硫酸化氧化鋯觸媒的合成及其催化反應之研究

Abstract

本研究利用水熱法，以Zr(O-nPr)4為前趨物、C16TAB為模版，成功合成了具中孔洞結構之氧化鋯 ，將sulfate負載至氧化鋯載體上，形成具中孔洞結構之硫酸化氧化鋯。初合成的硫酸化氧化鋯和硝酸鎵進行含浸，以得到鎵活化之中孔洞結構硫酸化氧化鋯觸媒(Ga-promoted sulfated mesoporous zirconia)，以m-GSZ表示之。 利用X光粉末繞射儀和氮氣吸/脫附儀等方法來鑑定材料的孔洞和結構性質。活化劑-鎵的加入使氧化鋯在高溫煅燒下仍能保有正方晶相(tetragonal phase)，同時亦穩定氧化鋯的中孔洞結構。我們選用正丁烷異構化反應來作為m-GSZ觸媒的活性測試反應，並根據文獻的報導和實驗結果，提出正丁烷異構化反應可能的反應機制。 為了比較活化劑對催化活性的影響，我們亦合成m-ASZ觸媒系統(以鋁作為促進劑)做比較。實驗發現，鋁和鎵加至硫酸化氧化鋯觸媒中皆能促進催化活性，其中鎵比鋁具有更佳的促進效應，藉由NH3-TPD及in-situ NH3-DRIFT的酸性鑑定，我們認為鋁增加了觸媒表面的酸性，而鎵對觸媒的酸性並無太大的改變。至此，研究重點轉至觸媒的氧化還原特性之探討，利用H2-TPR、in-situ n-butane DRIFT、Baeyer test等實驗，來了解鎵在硫酸化氧化鋯觸媒中扮演的角色，及其對正丁烷異構化反應的影響。

The isomerization of light paraffins to branched isomers was an important process in improving the octane number of gasoline. We have synthesized sulfated mesoporous zirconia using C16TAB as template and Zr(O-nPr)4 as zirconium precursor , then the promoter of Ga was introduced to give Ga-promoted sulfated mesoporous zirconia (donated as m-GSZ). The small amount of Ga not only retarded the phase transformation of zirconia from tetragonal to monoclinic, and retain more sulfur, but also stabilized the mesostructure of m-GSZ catalysts. The n-butane isomerization was used as the test reaction for the catalytic system at 200℃. We also compared the catalytic activities of the m-GSZ catalyst with the Al-promoted SZ catalyst, and the m-GSZ showed much stronger activities than the m-ASZ. From TPR experiment, in situ n-butane-DRIFT and using potassium permanganate as a powerful indicator, we could attribute the better activities of the m-GSZ catalysts to their better redox behavior. Now, we can obtain the excellent catalytic activities at a very low reaction temperature of 120℃ by controlling the ratio of n-butane to H2 of the reaction condition.