盐酸预处理对精对苯二甲酸精制用Pd/C催化剂微观结构的影响

摘要

采用不同浓度的盐酸对椰壳活性炭进行预处理,然后以浸渍法制备精对苯二甲酸(PTA)精制用Pd/C催化剂.通过SEM,EDS,TEM,XRD及氮气吸附-脱附测试等手段,研究盐酸预处理对Pd/C催化剂微观结构的影响,并探讨盐酸浓度与催化剂活性的关系.结果表明,活性炭载体经盐酸预处理后所得Pd/C催化剂的活性随盐酸浓度的增加呈先增大后减小的趋势,在盐酸浓度为0.6 mol/L时达到最大值.SEM和吸附-脱附表征结果均表明,盐酸预处理使Pd/C催化剂的平均孔径和中孔 孔体积有所增大.能谱测试结果表明,盐酸预处理后,催化剂的Pd含量变化不大,但由于盐酸对孔 结构造成的改变,使得表面下的活性炭基体暴露出来,出现O元素及微量的Si、Cl元素.盐酸预处理对Pd/C催化剂的物相未造成影响.由于盐酸预处理使催化剂的孔径及中孔孔体积增加,有效负载面积增大,促进Pd在载体上的分散,从而提高了催化剂的活性.%A commercial coconut activated carbon was firstly pretreated by HCl with different concentrations.Then the Pd/C catalyst used for purification of terephthalic acid was prepared using immersion method based on the pretreated carbon.By means of SEM,EDS,TEM,XRD and BET techniques,the impact of HCl pretreatment on microstructure and activity of the catalysts was investigated,and the relationship between HCl concentration and catalyst activity was explored.Test results show that the catalytic activity first increases and then decreases with the increase of HCl concentration and the maximum activity was obtained at the HCl concentration of 0.6 mol/L.SEM and adsorption-desorption tests show that the pretreatment of HCl can increase the average pore diameter and the mesopore volume of activated carbon.The EDS result indicates that the content of Pd maintains nearly constant,while some O element and trace impurity of Si and Cl appear on the carbon surface after HCl pretreatment.The changes of the surface morphology of HCl pretreated active carbon are not found.Owing to the increase of pore diameter and mesopore volume,the effective surface area of carbon for loading Pd component is increased,which is beneficial to the dispersity of Pd,and to the catalytic activity of Pd/C catalyst.