硅铝源对Ni-Pd-La/Hβ催化苯制环己基苯的影响

Effection of Si and Al Sources on Hydroalkylation of Benzene to Cyclohexylbenzene over Ni-Pd-La/Hβ

摘要:

用不同的硅、铝原料，通过水热晶化法合成Hβ分子筛，再以Hβ分子筛为载体，用浸渍法制备了Ni、Pd、La负载型多功能催化剂。采用XRD，BET，NH3-TPD，HR-TEM等手段对催化剂进行了表征，并将其用于催化苯（BZ）加氢烷基化制备环己基苯（CHB）。结果表明：相比于用硅溶胶和NaAlO2为硅、铝源经典方法所合成Hβ-3（25）（25代表Si/Al物质的量比为25）制备的催化剂Ni-Pd-La/Hβ-3（HAC-3），以硅酸四乙酯和金属铝粉为硅、铝源，所合成Hβ分子筛（Hβ-2）制备的催化剂Ni-Pd-La/Hβ-2（HAC-2）对BZ加氢烷基化制CHB反应具有较高活性和CHB选择性。重复使用过程中HAC-2呈现较好的稳定性。表征分析发现：HAC-2优越性能源自Hβ-2有着较高的比表面积，且铝原子在Hβ-2骨架中分布更均匀。以HAC-2（25）为催化剂、在190 ℃、2.0 MPa H2条件下反应90 min，BZ转化率可达46.8%，CHB的选择性可达79.6%。催化剂重复使用10次后，活性下降2.0%，表面积炭率只有0.21%。

Abstract:

Hβ zeolites were synthesized by hydrothermal crystallization with different Si and Al sources. Correspondingly, the multifunctional catalysts (Ni-Pd-La/Hβ) with Ni, Pd and La supported on these synthesized Hβ zeolites were prepared by impregnation method. These catalysts were characterized by XRD, BET, NH3-TPD, HR-TEM, and were used for catalytic hydroalkylation of benzene (BZ) to cyclohexylbenzene (CHB). The results showed that Ni-Pd-La/Hβ-2 (HAC-2) prepared using tetraethyl silicate and aluminum powders as Si and Al sources had higher activity and higher CHB selectivity than Ni-Pd-La/Hβ-3 (25) (HAC-3) (25 represents the molar ratio of Si to Al) prepared by the classical method using silica sol and NaAlO2 as Si and Al sources. HAC-2 showed good stability, which was attributed to the higher specific surface area of Hβ-2 and more uniform distribution of aluminum atoms in its frameworks. Under the conditions of HAC-2 (25) as catalyst, reaction temperature 190 ℃, hydrogen pressure 2.0 MPa and reaction time 90 min, the conversion rate of BZ and the selectivity of CHB were 46.8% and 79.6%. After reused after 10 times, the activity of the catalyst decreased by 2.0% and the carbon deposit was only 0.21%.