软模板导向合成多级孔丝光沸石及其苯的苄基化催化性能

Soft Template-directed Hierarchical Mordenites and Their Performance in Benzylation of Benzene with Benzyl Alcohol

通常认为丝光沸石是具有一维孔道结构的微孔沸石,在涉及大分子的催化反应中存在较为严重的扩散限制。以双季铵型表面活性剂C_(18)H_(37)N^+(CH_3)_2C_6H_(12)N^+(CH_3)_2C_6H_(13)(Br^-)_2(C_(18-6-6)Br_2)作为软模板,在水热条件下制备了多级孔丝光沸石分子筛。采用XRD、FT-IR、SEM、TEM、TG-DTG、N_2物理吸附、NH_3-TPD等手段对样品的晶体结构和物化性能进行了表征。结果表明,加入C_(18-6-6)Br_2制备了纳米棒定向排列的多级孔丝光沸石,而且可通过改变合成体系中C_(18-6-6)Br_2/SiO_2的比值,对样品的晶粒尺寸、介孔表面积和介孔孔容进行系统调变。在苯与苯甲醇的苄基化反应中,多级孔样品比传统微孔丝光沸石表现出更好的苄基化反应催化性能和显著提高的反应速率。多级孔丝光沸石优异的催化性能归因于介孔的存在使其具有更多的可接近活性位和更优异的质量传输性质,这种独特的多级孔丝光沸石在大分子催化转化反应中具有较大的应用潜力。

Mordenite is generally referred to be a one-dimensional micropore zeolite. The major drawback of this pore structure is severe diffusion limitations, especially for the reactions involving bulky molecules. Herein, hierarchical mordenites were successfully prepared through a soft-templating method using a diquaternary ammonium surfactant [C18H37N＋（CH3）2C6H12N＋（CH3）2C6H13（Br-）2, C18.6.6Br2 for short] as mesoporogen. The obtained samples were characterized by XRD, FT-IR, SEM, TEM, TG-DTG, N2 physical adsorption, and NH3-TPD techniques. The results show that the hierarchical mordenites with nanorods （20-40 nm in width） oriented-assembled structures are synthesized in the presence of the C18.6.6Br2 surfactant. Moreover, the crystal sizes, mesopore surface areas and mesopore volumes of hierarchical mordenites can be systematically tuned by changing the C18.6.6Br2/SiO2 ratios. More importantly, the hierarchical mordenites exhibit much higher catalytic activity and faster reaction rate in the benzylation of benzene with benzyl alcohol than the conventional mordenite. The remarkably enhanced catalytic performance of hierarchical mordenites may be attributable to the more accessible acid sites and much better mass transfer properties with the presence of mesopore. Thus, the special hierarchical mordenites reported here show a great potential for catalytic conversions involving bulky molecules.