Development of Aluminum-Gallium Mixed Oxide Catalysts for Selective Catalytic Reduction of NOx with methane

研究了Ga2O3-Al2O3固溶体的糖热合成，发现异丙铝和乙酰丙酮镓的混合物在1,4-丁二醇或1,5-戊二醇中在300℃下反应2h，生成具有缺陷尖晶石结构的γ型Ga2O3-Al2O3混合氧化物，其中镓离子选择性占据四面体位，铝离子优先占据八面体位。采用糖热法制备的Ga2O3-Al2O3催化剂在甲烷选择性催化还原Nox方面的活性高于用共沉淀法或溶胶-凝胶法制备的Ga2O3-Al2O3催化剂。糖热法制备的催化剂的活性与四面体Ga离子与总Ga离子的比例有关，因此可以得出下近邻位置有Al离子的四面体Ga离子是反应的活性位点。硼酸三甲酯或乙酸锌改性后的b或zn固溶体对甲烷的脱氮反应也有较高的活性。对于zn修饰的Ga2O3-Al2O3催化剂，其修饰不但减少了四面体Ga位的占比，反而提高了催化剂的结晶度，从而减少了吸附水的量，从而降低了水与Nox或甲烷的竞争吸附对水的抑制作用。在甲烷选择性催化还原Nox过程中，甲烷的活化是决定速率的步骤，水在催化剂上被强烈吸附，从而抑制了催化活性。因此，结晶度高的催化剂具有较高的活性。研究了在不同溶剂中溶剂热合成Ga2O3-Al2O3混合氧化物的方法，发现在二乙基三胺中反应可得到结晶度高的混合氧化物。用二乙基三胺制备的催化剂对甲烷选择性催化还原Nox具有较高的活性。少

Glycothermal synthesis of Ga2O3-Al2O3 solid solution was explored and it was found that the reaction of mixtures of aluminum isoproxide and gallium acetylacetonate in 1,4-butanediol or 1,5-pentanediol at 300℃ for 2 h yielded gamma-type Ga2O3-Al2O3 mixed oxides having a defect spinel structure, in which gallium ions selectively occupy the tetrahedral sites while aluminum ions preferentially occupy the octahedral sites. The Ga2O3-Al2O3 catalyst prepared by the glycothermal method had higher activity than those prepared by the corprecipitation or sol-gel method for selective catalytic reduction of Nox with methane. The activity of the catalyst prepared by the glycothermal method correlated with the ratio of the tetrahedral Ga ions to the total Ga ions and therefore it was concluded that the tetrahedral Ga ions with Al ions at the next-nearest-neighbor sites is the active site for the reaction. B-or Zn-modified solid solutions prepared by the addition of trimethyl borate or zinc acetate to … More the above-mentioned glycothermal reaction also had high activities for the deNOx reaction with methane. For the Zn-modified Ga2O3-Al2O3 catalyst, the modification rather reduced the population of the tetrahedral Ga sites but increased the crystallinity of the catalyst, which reduced the amount of adsorbed water, thus reducing the inhibitory effect of water caused by competitive adsorption of water with Nox or methane. In the selective catalytic reduction of Nox with methane, activation of methane is the rate-determining step and water is strongly adsorbed on the catalysts, thus inhibiting the catalytic activity. Therefore, the catalyst with high crystallinity had high activity. The solvothermal synthesis of the Ga2O3-Al2O3 mixed oxide in various solvents was examined and it was found that the reaction in diethylenetriamine gave the mixed oxide with high crystallinity. The catalyst prepared in diethylenetriamine had a quite high activity for selective catalytic reduction of Nox with methane. Less