关键词: 介孔材料, 甲基环己烷(MCH)脱氢, Pt/Al₂O₃催化剂, 载体-Pt前体界面作用, 铝羟基

Mesoporous alumina (MA) material with a well-developed mesoporous structure was synthesized by a facile solvent confined hydrolysis-condensation route without introducing organic template. In the proposed route, under vigorous stirring at 60 ℃, the hydrolytic agent (a mixture of deionized water and anhydrous ethanol with a volume ratio of 1:9) was added dropwise into a homogeneous aluminum isopropoxide solution with anhydrous ethanol as solvent to induce an incomplete hydrolysis of aluminum isopropoxide molecules, due to the water molecules dissolved in the anhydrous ethanol solvent exhibiting a significantly reduced accessibility with aluminum isopropoxide molecules; meanwhile, the presence of -OR groups in the intermediate aluminum species and the dispersion role from anhydrous ethanol resulted in an observably moderated condensation reaction of aluminum hydroxyl groups. Consequently, the local crosslinking of oligomerized aluminum hydroxyl species could lead to the formation of nanocluster-like Al-OH species surrounding the organic solvent molecules. During the subsequent solvent evaporation process at 60 ℃, the removal of organic solvent molecules filled in the spaces derived from the further cross-linking of nanocluster-like Al-OH species could drive the formation of mesostructure with uniform porous size. The crystal phase and textural and surface properties of the resulted MA material were further optimized by regulating the calcination conditions. Afterwards, the obtained MA-T samples calcined at different temperature were used as supports of Pt-based catalysts with a low Pt loading amount (w=0.5%) for methylcyclohexane (MCH) dehydrogenation. The characterization and catalytic results demonstrated that at an optimal calcination temperature of 450 ℃, the obtained MA-450 support possesses a γ-Al₂O₃ crystal phase and exhibits the highest specific surface area and pore volume. More importantly, the presence of abundant surface Ib type Al-OH species can effectively promote the homogenous dispersion of Pt precursor (chloroplatinic acid) molecules onto the surface of support MA-450 by an electrostatic interaction between Ib type Al-OH species and chloroplatinic acid molecules. As a result, the resultant catalyst Pt/MA-450 calcined at 500 ℃ for 3 h to thermally decompose the chloroplatinic acid molecules loaded on its surface displayed a notable catalytic activity with a maximum hydrogen evolution rate of 2112 mmol•g_Pt^–1•min^–1, which is inspiringly superior to the state-of-the-art supported Pt-based catalysts. Interestingly, even after a long-time reaction up to 100 h or regeneration, catalyst Pt/MA-450 still maintained more than 80% of original activity. The obviously boosted catalytic reactivity of catalyst Pt/MA-450 can be attributed to the highly homogenous dispersion of Pt active sites in a form of ultra-small nanoclusters and the excellent structural and textural properties of support MA-450, which play important roles in remarkably increasing Pt utilization efficiency and effectively improving the mass/heat transfer efficiency.

Key words: mesoporous material, methylcyclohexane (MCH) dehydrogenation, Pt/Al₂O₃ catalyst, interface interaction between support and Pt precursor, Al-OH