Solid-state reaction mechanism of ammonium molybdate with LaHY

doi:10.11949/j.issn.0438-1157.20160403

Abstract

Abstract:

Mass loss behavior in air and solid-state reaction mechanism of ammonium molybdate with LaHY were investigated by TG-DSC technique, and the physical structure, specific surface area, and surface acid sites by XRD, BET and NH₃-TPD techniques. It showed that surface speicies of Mo arising from decomposition of (NH₄)₆Mo₇O₂₄·4H₂O, over solid-state reaction of (NH₄)₆Mo₇O₂₄·4H₂O with LaHY, allocates in LaHY molecular sieve cage as molybdenum-oxygen clusters to form a single-phase complex nMoO_x·LaHY. The single-phase complex contributes to the lattice shrinkage, the reduced lattice parameter a₀, and the decrease in specific surface area. The as-prepared nMoO_x·LaHY possesses a slightly variation of weak acid center sites, an increase in medium strong acid center sites, a slightly decrease in strong acid center sites, and an increase in total acid sites, in comaprision with LaHY. The hydrodesulfulrization (HDS) performance of the single-phase complex nMoO_x·LaHY was evaluated by using 0.6% (mass) dibenzothiophene(DBT)/decane as the representative reactants. The conversion of DBT in HDS process at 290℃ and 310℃ over nMoO_x·LaHY catalyst with 5.0% (mass) of Mo loading, reached 56.38% and 88.79% under conditions of 4.0 MPa, 20 h^-1 of space velocity and 500:1 of H₂/oil volumetric ratio, which increased 12 and 28 percentage than that of MoO₃/Al₂O₃ with 20% (mass) of Mo loading, respectively. The nMoO_x·LaHY catalyst exhibited higher activity for DBT HDS reaction.

Key words: TG-DSC, solid-state reaction, single-phase complex, DBT, HDS

摘要：

采用TG-DSC技术研究了钼酸铵和LaHY在空气气氛中的失重行为，考察了钼酸铵与LaHY的固相反应机理，用XRD、BET和NH₃-TPD对其物相结构、比表面积和表面酸性进行了表征。结果表明，（NH₄）₆Mo₇O₂₄·4H₂O分解产生的表相Mo物种借助固相反应以金属-氧簇定位在LaHY分子筛体相笼中形成nMoO_x·LaHY单相复合体，引起分子筛的晶胞收缩，晶胞参数a₀减小，比表面积下降。制备的nMoO_x·LaHY较相应LaHY分子筛的弱酸中心变化较小，中强酸中心增加，强酸中心略有减少，总酸量增加。以质量分数为0.6%的二苯并噻吩/正癸烷溶液为模型反应物，评价了制备的nMoO_x·LaHY催化剂的加氢脱硫性能。负载Mo质量分数为5.0%制得的nMoO_x·LaHY催化剂在反应压力4.0 MPa，反应液时空速20 h^-1，H₂/原料液体积比500:1的实验条件下，290℃和310℃的二苯并噻吩加氢脱硫转化率达到了56.38%和88.79%，较相应负载Mo质量分数为20.0%制备的MoO₃/Al₂O₃催化剂分别提高了约12个百分点和28个百分点，表现出了较高的二苯并噻吩加氢脱硫反应活性。

关键词: TG-DSC, 固相反应, 单相复合体, 二苯并噻酚, 加氢脱硫

CLC Number:

O643

ZHANG Weiqing, GUO Wenguang, CHU Lili, KONG Lingpeng, JIN Guangzhou. Solid-state reaction mechanism of ammonium molybdate with LaHY[J]. CIESC Journal, 2016, 67(8): 3380-3386.

张伟清, 郭文光, 储丽丽, 孔令朋, 靳广洲. 钼酸铵与LaHY固相反应机理[J]. 化工学报, 2016, 67(8): 3380-3386.

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