非骨架铝在V中心形成过程中的作用

Role of non-Framework Aluminum Species for the Formation of V Center on Zeolites

采用电子顺磁共振 (ESR)技术 ,研究了非骨架铝在 H- MCM- 2 2分子筛上 V中心产生过程中的作用 .实验结果表明 ,H- MCM- 2 2分子筛经过高温处理后 ,产生一组六重超精细分裂信号 (A) ,该顺磁信号归属为 V中心 .超精细分裂 ,是由于与骨架铝相连的氧上的电子空穴与骨架铝相互作用的结果 ;分裂信号的产生与温度有关 ,其强度随着温度升高而增强 .不同晶体尺寸的 H- ZSM- 5分子筛的 ESR实验证实 ,容易形成非骨架铝的分子筛易形成 V中心 ,它产生于已经脱铝的分子筛或伴随着脱铝而产生 。

The role of the non\|framework aluminum species for the formation of V center at high temperatures on H\|MCM\|22 and H\|ZSM\|5 with different crystal sizes was studied using electron spin resonance technique. A set of six\|lines signal (denoted as A, g =2.048) was observed on H\|MCM\|22 after heat\|treatment under flowing helium, and its intensity increased with temperature. The paramagnetic center was identified as a hole of an electron trapped on oxygen atom bonding with a nearby framework aluminum atom. The formation of signal A might be related to the non\|framework aluminum species, which was further evidenced on the H\|ZSM\|5 with different crystal sizes by ESR technique. The mechanism might involve an electron transfer from the lattice oxygen to the vacant orbit of the non\|framework aluminum species.