微孔钼—钨—磷系列催化剂的合成及其催化作用研究

【作者】 彭革；

【导师】 胡长文；

【作者基本信息】 东北师范大学 ， 无机化学， 2002， 博士

【摘要】 利用Sol-Gel技术合成了杂多化合物Cs_xH_3-xPMo₁₂O₄₀/SiO₂，Cs_yH_5-yPMo₁₀V₂O₄₀/SiO₂和Cs_xH（5-x）PW₁₀V₂O₄₀/SiO₂。通过IR，UV-VIS和BET 吸附等温线进行了结构表征，表明 Cs_xH_3-xPMo₁₂O₄₀，Cs_yH_5-yPMo₁₀V₂O₄₀和Cs_xH_5-xPW₁₀V₂O₄₀的骨架结构在Cs_xH_3-xPMo₁₂O₄₀/SiO₂，Cs_yH_5-yPMo₁₀V₂O₄₀/SiO₂和Cs_xH_5-xPW₁₀V_2^-O₄₀/SiO₂网络中完整保留；它们是具有均匀的微孔结构的多酸硅溶胶杂化材料；研究了它们在液-固相体系中H₂O₂（30％）选择性氧化苯甲醇的氧化催化特性，作为耐水固体双功能催化剂具有很高的催化活性和对苯甲醛的产物选择性（接近100％），在Cs_xH_3-xPMo₁₂O₄₀/SiO₂，Cs_yH_5-yPMo₁₀V₂O₄₀/SiO₂和Cs_xH_5-xPW₁₀V₂O₄₀/SiO₂催化剂体系中，当x=1.5和y=2.5时氧化催化活性最高，几乎未观察到深度氧化产物苯甲酸的生成；钒引入SiO₂网络中的Cs_xH_3-xPMo₁₂O₄₀，Cs_yH（5-y）PMo₁₀V₂O₄₀和Cs_xH（5-x）PW₁₀V₂O₄₀骨架内部提高了氧化催化活性。 制备了Keggin阳离子与不同结构的杂多阴离子形成的新型无机材料(AlO₄Al₁₂（OH）₂₄（H₂O）₁2][SiW₁₁O₃₉ZCl]·11H₂O(略为Al₁₃-SiW₁₁Z；Z=Ni²⁺和Co²⁺、[AlO₄Al₁₂（OH）₂₄（H₂O）₁₂][P₂W₁₈O₆₂]Cl·33H₂O(缩为Al₁₃-P₂W₁₈)和[AlO₄Al₁₂（OH）₂₄（H₂O）₁2]₂[NaP₅W₃₀O₁₁₀]·24H₂O(缩为2Al₁₃-NaP₅W₃₀)。利用²⁷Al，²⁹Si，³¹PMAS NMR、TG、XRD和IR等手段，对这些新型无机材料进行了结构表征和物理化学性质研究。 利用Sol-Gel技术合成了MoP/SiO₂，NiMoP/SiO₂，CoMoP/SiO₂和WP/SiO₂催化剂。在微型连续流动反应器中，研究了它们在甲基苯胺（OMA）和丙基苯胺（OPA）加氢脱氮中的催化作用，同时还研究了它们对反应中扩散作用的影响，认为较细的粒子能克服扩散作用。在OMA和OPA反应中，认为C-N键断裂主要通过环上加氢和β-Hofmann消去机理。2-甲基环己胺（MCHA）是OMA反应的主要中间产物，在加入大量的环己烯后，才能被检测到，环己烯可以降低MCHA的吸附能力。通过检测MCHA中的甲基环己烷（MCH），解释C（sp³）-N键断裂是由于MCHA中的胺基被亲核取代。以此来证实，从甲基苯胺（OMA）到甲苯（MB）和从MCHA到MCH的反应路径机理是不相同的。在没有H₂S存在的条件下，Mo-W-P系列催化六峨；能提高 OMA iD OPA加氢脱氮的催化活性。同传统硫化物催化剂（必须有H。S存在）相比较，MOP／SIOZ fl化剂具有最高活性并且很大程度简化了反应的工艺过程。更多还原

【Abstract】 Heteropolyoxometalates are included in microporous silica, CsxH3-xPMo12O40/SiO2, CsyH5-yPMo10V2O40/SiO2 and CsxH5-xPW10V2O40-/SiO2 have been synthesized by a sol-gel technique and characterized by IR, UV-V1S, X-ray and N2 adsorption isotherms. IR and UV-VIS data indicate that the identities of CsxH3-xPMo12O40, CsyH5-yPMo10V2O40 and CsxH5-xPW10V2O40 are preserved within these synthesized compounds. TEM image and BET adsorption isotherms confirm the presence of nanometer particles and microporous structures. X-ray powder patterns prove that the cesium salts of the heteropolyoxometalates are uniformly dispersed in the silica network. As insoluble solid bifunctional catalysts, they show high catalytic activity and selectivity for selective oxidation of benzyl alcohol into benzyl aldehyde by H2O2 in liquid-solid systems. The highest activity is observed at x = 1.5 or y = 2.5 in CsxH3-xPMo12O40/SiO2, CsyH5-yPMo10V2O40/SiO2 and CsxH5-xPW10V2O40/SiO2, respectively.A novel class of inorganic materials, [AlO4Al12(OH)24(H2O)12]-[SiW11O39ZCl].11H2O (abbreviated Al13.SiW11Z, Z = Ni or Co), consisting ofKeggin cations and Keggin anions, has been synthesized and characterized by IR, NMR, X-ray and TGA. The infrared spectral and the MAS NMR spectroscopic data for the Al13-SiW11Z indicate that the identities of the clusters are preserved in the monolithic crystal Al13-SiW]]Ni and gel Al13-SiW11Co, and the Al13-SiW11Z is indeed a more symmetric structure. The X-ray powder pattern of the gel Al13-SiW11Co demonstrates its swelling properties.The hydrodenitrogenation (HDN) of o-methylaniline (OMA) and o-propylaniline (OPA) has been studied in a continuous microflow reactor over MoP, NiMoP and CoMoP catalysts supported on SiO2. Diffusion effects in the HDN of OMA and OPA were studied and it was found that the intermediates could not diffuse out of the pores fast enough to be detected. To avoid diffusion limitation, the particle sizes of the catalysts were reduced. The major part of theC-N cleavage of OMA and OPA take place via ring hydrogenation and p-Hofmann elimination. The HDN of 2-methylcyclohexylamine (MCHA) was studied because it is an intermediate in the HDN of OMA, which can be detected in addition to the main products methycyclohexene (MCHE) and methylcyclohexane (MCH) when a high quantity of cyclohexene was added to OMA during its HDN. MCHA is not observed in the HDN of OMA alone, because of its strong adsorption constant and high rate constant for reacting further to MCHE and MCH. Adding cyclohexene decreases the adsorption of MCHA, thus enabling its detection. The selectivity of MCH in the HDN of MCHA was about 20% at low conversion. The detection of 2-methylcyclohexane in the HDN of MCHA explains the C(sp3)-N bond cleavage showing that MCH is formed via nucleophilic substitution of the amine group of MCHA. Moreover, it was proved that the mechanism of the pathway from OMA to MB is different in the pathway from MCHA to MCH [direct C(sp3)-N]. All phosphides can increase reaction activity in the absence of H2S for the HDN of OMA and OPA. Prepared with traditional MoS2 system catalysts, MoP/SiO2 catalyst had the highest activity and simplified the technology process at the high degree.更多还原