金屬-氧化鈦複合觸媒微結構之控制與改良(2/2)

Abstract

本研究主要探討二氧化鈦運用於光觸媒催化由甲醇水溶液中形成氫之相關議題。在此報告中將總 結兩項議題之研究結果，包括(1)觸煤煅燒氣氛(2)添加銅顆粒對觸媒活性之影響。二氧化鈦係經 由溶膠-凝膠法製成後於Ar, 合成空氣(air)，氮(N2), 氫(H2 3% in N2) and 真空(vacuum;~5 x 10 -3 torr) 。對於由甲醇水溶液中形成氫之活性高低次序為Ar > air> N2 > vacuum ~ H2 。光譜分析顯示 氫與真空導致之低活性源於低表面氫氧基與高晶格缺陷密度。Ar 導致之高活性源於高表面氫氧 基及較多之低能隙激發位置(site)。添加表面銅顆粒大幅提昇TiO2 活性。光譜分析顯示銅顆粒在 反應過程中氧化至具最佳活性之最佳氧化態，而此氧化態無法經由空氣中熱氧化達成。將銅離子 溶入氧化鈦晶格中降低活性。

TiO2 photocatalysts for hydrogen production from aqueous methanol solution is the main subject of this work, Studies on two issues are reported here, including (1) the effect of calcination atmosphere and (2) the effect of Cu metallization. TiO2 catalysts were synthesized by a sol-gel process followed by calcination at 400 o C in Ar, air, N2, H2 (3% in N2) and vacuum (~5 x 10 -3 torr), respectively. Toward H2 production from a water/methanol (vol. ratio= 1.4/1) solution, the catalysts exhibited activities in the order, according to calcination atmosphere, of Ar > air> N2 > vacuum ~ H2. The low activity resulting from either vacuum or H2 calcination was ascribed to a reduced coverage of surface hydroxyl and high bulk defect density, based on the x-ray photoelectron and UV-visible spectroscopic analyses, while the high activity from Ar calcination is to enhanced visible-light excitation. For studying the effect of Cu, Cu particles have been deposited on TiO2 by incipient-wetness impregnation followed by low-temperature (400 o C) calcination/reduction, and the metallization process leads to significant, up to 10 folds, enhancement in photocatalytic activity of TiO2 for H2 production from aqueous methanol solution. Spectroscopic studies indicated that the metallic Cu particles were oxidized to have an optimum valence that can not be achieved by thermal oxidation. Dissolution of Cu ion in TiO2 lattice, in contrast, led to reduction in the activity.