摘要
本研究利用浸渍法制备了Ru/TiO2催化剂,并在光照和加热两种条件下考察了其催化二氧化碳与氢的反应,发现催化剂在两种条件下均可引发显著的甲烷化反应（CO2＋4H2→CH4＋2H2O）。结果显示,在光照和加热（150~350℃）条件下,CH4为唯一含C产物。而在更高温度的加热条件下（〉400℃）除了生成CH4外,还产生少量CO副产物,表明反应温度对产物选择性有显著影响。随着反应温度由150℃升高到550℃,对于不同负载量的担载Ru催化剂,CO2转化率均先增加后降低,其中在Ru担载量为1.5wt%Ru/TiO2催化剂上CO2转化率在350℃时达到最高,为77.58%。而在温度〉400℃条件下,CO的选择性也随反应温度的升高而逐渐增加。综合反应结果和XRD、XPS和N2吸附-脱附等表征结果,发现二氧化碳与氢在光照和加热条件下（150~550℃）反应机制不同。在光照条件下,光激发电子首先被金属Ru捕获,进而将吸附在金属Ru上的二氧化碳还原,活性物种经由Ru C中间体形成CH4。而加热条件下（150~550℃）,H2先被Ru活化成氢原子,氢原子还原吸附在催化剂表面的CO2形成Ru C中间体,最后Ru C中间体进一步加氢生成CH4。虽然在两种反应条件下经历相同的中间体,但是中间体的形成路径不同,即反应物CO2被活化的方式不同,因而产物选择性不同。
CO2 hydrogenation was carried out over Ru/TiO2 catalysts prepared by wet impregnation method. It was found that CO2 methanation （CO2 ＋ 4H2 → CH4 ＋ 2H2O） could be catalyzed by Ru/TiO2 both under UV irradiation and heating. Results showed that CH4 was the only C-contained product under UV irradiation in temperature range from 150-350℃, while both CH4 and CO （minor product） were formed at temperature higher than 400℃ under heating conditions. This indicated that reaction temperature affected obviously on selectivities of products. For all the catalysts with different Ru loadings, CO2 conversion increased firstly and then decreased from 150℃ to 550℃, and corresponding maximum value of CO2 conversion of 77.58% was achieved at 350℃ over 1.5wt% Ru/TiO2 catalysts. Further increasing of reaction temperature over 400℃ led to the increase of CO selectivity. Based on re- action data, XRD, XPS and N2 adsorption-desorption characterization results, we found that CO2 hydrogenationoccurred in different ways under UV irradiation and heating conditions （150-550℃）. Under UV irradiation, excited electrons were firstly trapped by Ru site and then these electrons reduced CO2 species, which was adsorbed on Ru surface to form CH4 via RuC intermediate. However, under heating condition （150-550℃）, H2 was first decom- posed into H atoms over Ru site, then the adsorbed CO2 species on Ru site was reduced by H atoms to form RuC intermediate. Finally, RuC reacted with H atoms to produce CH4. Although CO2 hydrogenation was taken place via same intermediate under UV irradiation and heating conditions, the RuC intermediate was formed in different ways, i.e., the activation of CO2 was induced in the different routes, therefore the different selectivities of products were obtained under UV irradiation and heating at temperature higher than 400℃ consequently.
出处
《无机材料学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第12期1287-1293,共7页
Journal of Inorganic Materials
基金
国家重点基础研究发展规划项目(973计划
2009CB22003)
国家高技术研究发展计划项目(863计划
2012AA051501)
国家自然科学基金(21173242
21433007)~~
关键词
光催化
加热
CO2加氢
RU
photocatalytic
heating
CO2 hydrogenation
Ru
