MO(M=Cu和Ni)/TiO_2/γ-Al_2O_3催化剂在CO+O_2反应中的活性

Activities of MO(M=Cu and Ni)/TiO_2/γ-Al_2O_3 Catalysts in CO Oxidation

采用X射线衍射(XRD),程序升温还原(TPR)等表征手段考察了TiO2改性对CuO(或NiO)在γ-Al2O3表面上分散以及还原性能的影响,同时检测了这些改性的催化剂在CO+O2反应中的活性。结果表明:TiO2的改性使得CuO和NiO在γ-Al2O3载体上的分散复杂化,产生了多种状态的氧化铜(氧化镍)物种。当负载量低于其在γ-Al2O3上的分散容量(0.56mmol Ti4+/100m2γ-Al2O3)时,TiO2的加入主要是抑制了CuO和NiO在γ-Al2O3载体上的分散;而当负载量远大于其分散容量时,出现了CuO和NiO在晶相TiO2(锐钛矿)上的分散。无论其负载量如何,TiO2的加入促进了CuO的还原。因此,在250℃的CO+O2反应中,改性的催化剂中具有更多的活性位,因而显示出更高的活性;相反,TiO2的改性则抑制了NiO的还原。因此,在350℃的CO+O2反应中,可还原的氧化镍的量明显少于未经改性的催化剂,导致改性催化剂的活性降低。

The influence of titania on the properties of CuO/γ-Al2O3 and NiO/γ-Al2O3 catalysts was investigated using X-ray diffraction （XRD） and temperature programmed reduction （TPR）, and CO oxidation reaction. It is indicated that, the modification of TiO2 makes the dispersion of CuO （and NiO） supported on γ-Al2O3 complicated, CuO （and NiO） of various states coming into being. Dispersion of CuO and NiO on the surface of γ-Al2O3 is greatly suppressed when pre-loading amount of TiO2 is lower than its dispersion capacity on the surface of γ-Al2O3 （0.56 mmol Ti^4＋/100 m^2 γ-Al2O3）. Whereas the suppressing effect holds, as pre-loading amount of TiO2 is far beyond the dispersion capacity, the dispersion of CuO and NiO on the surface of TiO2 （anatase） occurs. The presence of TiO2 evidently promotes the reduction of CuO, hence leads the CuO/TiO2/γ-Al2O3 catalysts to be much more active than those without TiO2 in CO oxidation reaction at 250 ℃. In contrast, due to strong interactions between NiO and TiO2 （and γ-Al2O3）, NiO reduction is greatly suppressed in the modified catalysts. As a result, NiO/TiO2/γ-Al2O3 catalysts exhibit lower activities in CO oxidation reaction at 350 ℃ than those without TiO2.