Development of useful metal catalysts for hydrotreatment of diesel fuel to decrease particulate matters in diesel exhaust.

为了开发适用于柴油中芳烃加氢的金属催化剂，我们研究了在二甲基二硫醚作为硫化合物的存在下，在负载Pd催化剂上萘加氢。（1）研究了Pd/Al_2O_3、Pd/SiO_2、Pd/TiO_2、Pd/TiO_2-SiO_2和Pd/TiO_2-Al_2O_3催化剂在二甲基二硫（DMDS）存在和不存在下的萘加氢反应。（2）采用共浸渍法制备了Pd-Pt/TiO_2和Pd-Pt/TiO_2催化剂，考察了它们在萘加氢反应中的催化活性。所有Pd-Pt/TiO_2催化剂的飞行时间都比Pt/TiO_2催化剂高。Pd含量为50mol%的Pd-Pt/TiO_2催化剂具有最高的飞行时间。Pd含量为80mol%时，Pd-Pt/Al_2O_3的飞行时间最长。含80mol%Pd的Pd-Pt/Al_2O_3的飞行时间分别是Pd/Al_2O_3和Pt/Al_2O_3的8倍和18倍。(3)As与Pd/Al_2O_3相比，Pd/TiO_2在DMDS存在和不存在的情况下均表现出较高的飞行时间和耐硫性。用程序升温还原法（H2S-TPR）测定了Pd-S键的强度。结果表明，硫化态Pd/TiO_2中H_2S的脱附发生在553 K，而硫化态Pd/Al_2O_3中H_2S的脱附需要更高的温度（773 K），表明Pd/TiO_2中的Pd-S键明显弱于Pd/Al_2O_3。因此，在Pd/TiO_2中，Pd金属的清洁表面高度暴露为二甲基二硫存在下萘加氢的活性中心。

To develop useful metal catalysts for hydrogenation of aromatic hydrocarbons in diesel fuel, we have studied naphthalene hydrogenation over supported Pd catalysts in the presence of dimethyldisulfide as a sulfur compound.(1)Naphthalene hydrogenation over Pd/Al_2O_3, Pd/SiO_2, Pd/TiO_2, Pd/TiO_2-SiO_2, and Pd/TiO_2-Al_2O_3 cal alysts was studied in the presence or absence of dimethyldisulfide (DMDS). As a results, the order of TOP (turn over frequency) was Pd/TiO_2-Al_2O_3 > Pd/TiO_2-SiO_2 > Pd/TiO_2 > Pd/Al_2O_3 > Pd/SiO_2(2)Pd-Pt/TiO_2 and Pd-Pt/TiO_2 catalysts were prepared by a co-impregnation method and evaluated in the hydrogenation of naphthalene in the presence of dimethyldisulfide. All Pd-Pt/TiO_2 bime tallic catalysts showed the higher TOF than the Pt/TiO_2 catalyst. Pd-Pt/TiO_2 containing 50mol% Pd showed the highest TOF in the catalysts tested. Meanwhile The highest TOF of Pd-Pt/Al_2O_3 were obtained at the content of 80mol% Pd. The TOF of Pd-Pt/Al_2O_3 containing 80mol% Pd was 8 times and 18 times higher than those of Pd/Al_2O_3 and Pt/Al_2O_3, respectively.(3)As compared with Pd/Al_2O_3,Pd/TiO_2 showed high TOF and sulfur tolerance, in both the presence of DMDS and the absence of DMDS. Pd-S bond strength was determined by temperature-programmed reduction (H_2S-TPR) profiles. The results show that desorption of H_2S from sulfided Pd/TiO_2 occurs at 553 K, whereas desorption of H_2S from sulfided Pd/Al_2O_3 requires a higher temperature (773 K), indicating that the Pd-S bond in Pd/TiO_2 is significantly weaker than that in Pd/Al_2O_3. Consequently, in Pd/TiO_2 clean surfaces of Pd metals are highly exposed as active sites for the naphthalene hydrogenation in the presence of dimethyldisulfide.