EPR technique was used to investigate the formation and variation of free radicals on the catalyst and in the liquid phase after adsorption of 2,2,6,6-tetramethyl-piperdin-4-one(TMPDO)and 2,2,6,6-tetramethyl-piperdin-4-one oxime(4-NOH-TMPD)over hollow titanium silicalite(HTS)zeolite in the presence of H2O2. The results showed that the EPR signal of HO·in the HTS/H2O2 system was significantly decreased after 4-NOH-TMPD adsorbed on HTS,while the signal intensity of O-2·free radical increased by 28 times and that of TiOO-·increased by more than double. Moreover,Simifonia software simulation indicated that the free radicals of TiOO-·(η2)…4-NOH-TMPD were formed in the HTS/H2O2/4-NOH-TMPD system, and the stabilization of the double-site adsorption of 4-NOH-TMPD in HTS/H2O2 to TiOOH was the fundamental cause for the above changes. Furthermore,it was found that as 4-NOH-TMPD added into the HTS/H2O2 system,the signal of free radicals on the catalyst almost disappeared while two new free radicals were formed due to the interaction between acetone oxime in liquid phase and Ti—OO-· or O-2· free radicals, giving HTS/H2O2/4-NOH-TMP system with the catalytic activity for the oxidative coupling of acetone oxime to form 2,3-dimethyl-2,3-dinitrobutane(DMNB).%采用电子顺磁共振(EPR)技术考察了中空钛硅分子筛(HTS)吸附2,2,6,6-四甲基哌啶-4-酮(TMPDO)及2,2,6,6-四甲基哌啶-4-酮肟(4-NOH-TMPD)后,在H2O2存在下催化剂表面和液相中自由基生成的变化.结果表明,在HTS被4-NOH-TMPD吸附改性后,原HTS/H2O2体系溶液中存在的·OH信号强度明显下降,而O-2·自由基信号强度增加28倍,且催化剂表面TiOO-·信号强度增加了1倍多.通过Simfonia软件模拟分析发现,HTS/H2O2/4-NOH-TMPD体系中主要生成了结构为TiOO-·(η2)…4-NOH-TMPD的自由基.4-NOH-TMPD在HTS/H2O2中由双位吸附产生的对TiOOH的稳定作用是导致上述变化的根本原因.进一步研究发现,HTS/H2O2体系中加入4-NOH-TMPD 后,催化剂表面的自由基信号基本消失,而液相中丙酮肟与Ti—OO-·或O-2自由基作用生成了2种新自由基,使HTS/H2O2/4-NOH-TMPD体系具有催化丙酮肟氨氧化偶联生成2,3-二甲基-2,3-二硝基丁烷(DMNB)的活性.
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