不同粒径的Ni/SiO2催化剂上CH4和CO2吸附活化的漫反射傅里叶变换红外光谱研究

 采用原位漫反射傅里叶变换红外光谱研究了CH4和CO2在不同粒径的Ni/SiO2催化剂上的吸附及活化. 结果表明,在不同粒径的催化剂上,检测到有CH4解离生成的CHx(x=1～3)物种,以及催化剂表面吸附的CHx物种与表面-OH 作用生成的CHx-O物种. CH4的裂解强烈依赖于催化剂表面Ni颗粒的大小,在粒径8 nm左右的Ni颗粒上, CH4较易解离; CO2难以直接在Ni/SiO2催化剂表面发生解离吸附,但CH4解离生成的吸附H对CO2的解离吸附具有明显的促进作用; CH4与CO2共吸附时,较小粒径的Ni可以促进CO2与表面氧物种发生反应,生成单齿表面碳酸盐物种.

DRIFTS Study on Adsorption and Activation of CH4 and CO2 on Ni/SiO2 Catalyst with Various Ni Particle Sizes

The adsorption and activation of CH_4 and CO_2 on Ni/SiO_2 catalyst with different Ni particle sizes were investigated by diffuse reflectance infrared Fourier transform spectroscopy. CH_x species (x=1-3) were observed on the catalyst with different Ni particle sizes when CH_4 was adsorbed on its surface. The CH_3-O species was also detected as the result of an interaction of CH_x species with surface hydroxyl groups. The dissociation of CH_4 depended intensively on the Ni particle size. CH_4 dissociated more easily on the Ni/SiO_2 catalyst with a Ni particle size of approximate 8 nm. CO_2 was very difficult to dissociate on the Ni/SiO_2 catalyst, while the adsorbed H from CH_4 dissociation promoted the dissociation of CO_2. Small Ni particles might be helpful to hydrogen overflow to the support for CO_2 activation. In co-adsorption of CH_4 and CO_2, the monodentate carbonate species was observed on the Ni/SiO_2 catalyst with smaller Ni particle size, which indicated that smaller Ni particles could promote the reaction of CO_2 with surface oxygen species.