硫存在下Beta沸石负载钯催化剂上的芳烃加氢性能研究

Investigation on beta zeolites supported palladium catalysts for aromatics hydrogenation in the presence of sulfur

采用浸渍和离子交换方法,制备了一系列H Beta沸石负载钯催化剂,并用XRD,N2吸附和氨程序升温脱附进行了表征。采用连续流动固定床反应器,在总压4MPa,270℃,液体空速为16h-1和硫的质量分数为100×10-6的条件下进行了四氢萘的加氢反应。实验结果表明,钯催化剂的催化性能与催化剂制备方法及载体的硅铝比有关系。对Pd Beta25(25是硅铝比,下同)来说,离子交换(IE)催化剂的加氢活性高于对应的初湿浸渍(IWI)样品。对于所有离子交换催化剂,Pd Beta80(IE)在整个反应期间催化活性及抗硫性最好。Pd Beta25(IE)四氢萘的初始转化率高达77%,失活最快,8h降到10%;Pd Beta60(IE)初始转化率为60%,8h后为16%;Beta80负载催化剂最稳定,起始和8h后转化率分别为75%和55%。离子交换的Beta80负载Pd催化剂的优良催化活性可以归结为催化剂中有较高比例的中强和强酸性位的存在,尤其中强酸比例较高,同时较多中孔的存在也是其中的影响因素之一。少量Al2O3的添加可以改善催化剂的活性。

A series of beta zeolites supported palladium catalysts were prepared by ion exchange (IE) or incipient wetness impregnation (IWI). The characterizations such as XRD,N_2 adsorption and temperature-programmed desorption(TPD)of ammonia were carried out. Hydrogenation of tetralin was conducted with a continuous-flow fixed bed micro-reactor under 4MPa, 270℃,WHSV 16h^(-1) and 100mg/kg S (thiophene as S source). It is found that catalytic behaviours of the supported Pd catalysts depend both on the preparation methods and on the properties of supports. For Pd/Beta25,the catalytic activity of the sample prepared via ion exchange (IE for short) is superior to the initial wetness impregnated(IWI for short)one. Among three ion exchanged catalysts, Pd/Beta80(IE) is most active and sulphur tolerant during the whole time on stream. Pd/Beta25(IE) deactivates most rapidly because the conversion of tetralin decreases from the initial 77% to 10% after 8h. With Pd/Beta60(IE), the corresponding conversion are 60% and 16% respectively. And with Pd/Bera80(IE) those are 75% and 55% respectively. The excellent activity of Pd/Beta80(IE) can be attributed to the carrier's higher strong acidity/weak acidity ratio, especially the presence of more medium strength acid sites and the mesopores structure. Besides,the addition of alumina to Pd/Beta25 is favourable to improving its catalytic activity.