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

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、NH_(3)-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NaAlO_(2)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,下同)制备的催化剂4%Ni-0.2%Pd-3%La/Hβ-3(25)(HAC-3,其中,百分数为金属单质质量与Hβ质量之比,下同),以正硅酸四乙酯和金属铝粉为硅、铝源,所合成Hβ分子筛[Hβ-2(25)]制备的催化剂4%Ni-0.2%Pd-3%La/Hβ-2(25)(HAC-2)对BZ加氢烷基化制备CHB反应具有较高活性和CHB选择性。重复使用过程中HAC-2(25)呈现较好的稳定性。表征分析发现:HAC-2(25)优越性能源自Hβ-2(25)有着较高的比表面积,且铝原子在Hβ-2(25)骨架中分布更均匀。以HAC-2(25)为催化剂、在210℃、2.0 MPa H_(2)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%。

Hβ zeolites were synthesized by hydrothermal crystallization with different Si and Al sources. Correspondingly, multifunctional catalysts with Ni, Pd and La supported on these synthesized Hβ zeolites were prepared by impregnation method. These catalysts were characterized by XRD, BET, NH_(3)-TPD, HRTEM, and were used for catalytic hydroalkylation of benzene(BZ) to cyclohexylbenzene(CHB). The results showed that 4%Ni-0.2%Pd-3%La/Hβ-2(25) [HAC-2(25)] prepared using tetraethyl silicate and aluminum powders as Si and Al sources had higher activity and higher CHB selectivity than 4%Ni-0.2%Pd-3%La/Hβ-3(25) [HAC-3(25)](25 represents the molar ratio of Si to Al, the percentages are the ratio of elemental metal mass to Hβ mass, the same below) prepared by the classical method using silica sol and NaAlO_(2) as Si and Al sources. HAC-2(25) showed good stability, which was attributed to the higher specific surface area of Hβ-2(25) and more uniform distribution of aluminum atoms in its frameworks. Under the conditions of HAC-2(25) as catalyst, reaction temperature 210 ℃, 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% respectively. After reused for 10 times, the activity of the catalyst decreased by 2.0% and the carbon deposit was only 0.21%.