负载型纳米Au/HZSM-5催化剂的制备及其在甲烷吸附中的应用

Preparation of supported nano Au / HZSM-5 catalysts and their application for methane adsorption

采用离子交换法制备负载型纳米HZSM-5分子筛,采用负压-沉积沉淀法制备负载型纳米Au/HZSM-5催化剂,对载体及催化剂进行XRD、UV-Vis、TEM、XPS、NH3-TPD和FT-IR等表征,并评价催化剂的甲烷吸附性能。XRD与TEM表征结果表明,N2气氛焙烧的2.0%Au/HZSM-5催化剂金粒子尺寸较小,为（5~10）nm;UV-Vis表征结果表明,焙烧导致负载金的价态由离子态转为零价态,且N2气氛焙烧的2.0%Au/HZSM-5催化剂上零价金的吸收峰较弱,即相应的颗粒度较小;XPS表征结果表明,金负载量越高,催化剂上零价金占总金的比例越高;NH3-TPD表征结果表明,金负载量较小时,催化剂强酸中心峰面积较载体下降,负载量较大时,强酸和弱酸中心峰面积均下降;FT-IR表征结果表明,低温下金催化剂能将甲烷转化为含有烯烃双键的吸附物种,显示出载金催化剂对甲烷较强的C—H键活化能力。

HZSM-5 zeolite and supported nano Au / HZSM-5 catalysts were prepared by ion exchange method and negative-deposition precipitation method,respectively. The as-prepared zeolite and catalysts were characterized by XRD,UV-Vis,TEM,XPS,NH3-TPD and FT-IR,and their performance for methane adsorption were evaluated. The results of XRD and TEM showed that Au particle size of 2. 0% Au / HZSM-5catalyst calcined under N2 atmosphere was（ 5-10） nm. The results of UV-Vis indicated that the calcination led to Au change from ion-valent state into zero-valent state,and Au0 absorption peak of 2. 0% Au / HZSM-5catalyst calcined under N2 atmosphere was weaker,which indicated that the corresponding particle size was smaller. The results of XPS showed that the higher the Au loading was,the higher the proportion of zero-valent Au to total Au of the catalyst was. The results of NH3-TPD showed that compared with HZSM-5zeolite,the peak area of strong acid center of Au / HZSM-5 catalysts declined when the Au loading was smaller,and both strong and weak acid centers decreased when the Au loading was higher. The results ofFT-IR showed that Au / HZSM-5 catalysts could convert methane to adsorbed species containing olefin double bond at low temperature,showing better C—H bond activation capability for methane.