Mo-SiO2-C3H6催化反应体系的ESR动态表征

文章考察了Mo-SiO₂催化剂体系在丙烯歧化反应过程中的动态ESR波谱,发现在催化歧化反应过程中有两种Mo⁵⁺顺磁中心,一种为扰动八面体配位,g_||=1.89,g_⊥=1.94;另一种为扰动四棱锥配位,g_||=1.86,g_⊥=1.95。测得同位素^95,97Mo⁵⁺的各向异性超精细耦合常数A_||=90.3×10^-4cm^-1,A_⊥=44.8×10^-4cm^-1;观测到反应产生的积炭信号,g≈2.0O₂;氧阴离子自由基信号g₁=2.018,g₂=2.011,g₃=2.005。用LCAO-MO理论对上述Mo⁵⁺的ESR波谱进行计算,求得分子轨道系数,发现并总结出△g_||/△g_⊥与△g成直线关系,并建议用△g_||/△g_⊥=4(△E(B₂→E))/(△E(B₂→B₁)(β₁/ε)²之比值作为衡量C_4v扰动程度的尺度。

DYNAMIC ESR CHARACTERIZATION OF Mo-Si0_2 -C_3 H6 CATALYTIC SYSTEM

ESR Spectra of molybdenum supported catalysts(Mo-SiO₂) were recorded with various contact time with propene.Two types of Mo⁵⁺-paramegnetic centers were formed during the course of reaction. The one having g_||=1.89,g_⊥=1.94 is due to the distorted octahadral coordination, while the other with g_||=1.86,g_⊥=1.95 is a square pyramidal distorted species.However,they are both approximately of C_4v symmetry. The anisotropic surperfine coupling contants A_||=90.3×10^-4cm^-1,A_⊥=44.8×10^-4cm^-1 of ^95,97Mo⁵⁺-were also detected. Meanwhile, the signals occurerd at ca. g=2.002 and g₁=2.018,g₂=2.011,g₃=2.005 were assigned to coking from propene and anionic radical 0₂^- respectively. LCAO-MO approximate calculations of data led to a set of molecular orbital coefficients. It was found that the plot of △g_||/△g_⊥ vs. △g is linear. Suggestion was made to employas △g_||/△g_⊥=4(△E(B₂→B₁))/(△E(B₂→E)·(β₁/ε)² a better measure of the extent of C_4v distortion for Mo⁵⁺.