覆炭载体镍催化剂脱氢活性和表面酸性研究

以制备的覆炭γAl2O3(CCA)为载体,制备了Ni/CCA系列催化剂,并对其环己烷脱氢活性进行了考察;以吡啶为探针分子,用热重分析(TG)和差示热分析(DTA)技术测定了Ni/CCA催化剂的表面酸性,并计算了Ni/γ-Al2O3和Ni/CCAⅡ两种催化剂的脱吡啶活化能。结果表明,Ni/CCA催化剂的脱氢活性优于Ni/γ-Al2O3催化剂;CCA载体的覆炭量对Ni/CCA催化剂的脱氢活性有一定的影响,当覆炭的质量分数在7.92％时出现脱氢活性峰,并且Ni/CCA催化剂具有较好的低温脱氢活性;CCA载体和Ni/CCA催化剂表面的吡啶物理吸附量和化学吸附量均低于γ-Al2O3载体和Ni/γ-Al2O3催化剂,CCA载体和Ni/CCA催化剂的脱附化学吸附毗啶的DTA曲线上有两个吸热峰,说明在CCA载体和Ni/CCA催化剂上有两个表面酸性中心;求得吡啶在Ni/γ-Al2O3和Ni/CCAⅡ催化剂的强酸中心的脱吡啶活化能分别为188 kJ/mol和225 kJ/mol,在弱酸中心的脱吡啶活化能分别为30 kJ/mol和31 kJ/mol。

Dehydrogenation Activity and Surface Acidity of Ni Catalyst Supported on Carbon Covered Alumina

A series of Ni/CCA catalysts with carbon covered alumina (CCA) as support were prepared and their dehydrogenation activity were evaluated. The surface acidity of the catalyst was measured by TG and DTA using pyridine as adsorbent. The activation energy of pyridine desorption from Ni/γ - Al2O3 and Ni/CCA Ⅱ catalysts were also calculated. Dehydrogenation activity of Ni/CCA catalyst was better than that of Ni/γ-Al2O3 catalyst. Carbon cover content has some effect on dehydrogenation activity of the Ni/CCA catalyst, and the peak of dehydrogenation activity appears at a carbon cover content of 7.92% . Ni/CCA catalyst exhibited excellent activity at low temperature. Physically and chemically adsorbed pyridine amount of CCA carriers and Ni/CCA catalysts were lower than that of γ -Al2O3 carriers and Ni/γ-Al2O3 catalyst. There were two endothermic peaks on the pyridine desorption DTA curves, which demonstrated that CCA carriers and relevant Ni catalysts had two kinds of surface acidity centers corresponding to weak and strong acid centers respectively. The two endothermic peak temperatures of Ni/CCA catalysts were higher than that of Ni/γ -Al2O3 catalyst, which indicated that the acid strength of Ni/CCA catalysts was higher than that of Ni/γ-Al2O3 catalyst. However,the weak acid amount of Ni/CCA catalysts was lower than that of Ni/γ-Al2O3 catalyst. The activation energy of pyridine desorption from strong acid centers of Ni/CCA Ⅱ catalyst and Ni/γ-Al2O3 catalyst were 225 kJ/mol and 188 kJ/mol respectively, that from weak acid centers were 31 kj/mol and 30 kj/mol respectively. This also showed that acid strength of Ni/CCAⅡ catalysts was higher than that of Ni/γ-Al2O3 catalyst.