还原处理对CuY催化剂微观结构及甲醇氧化羰基化活性的影响

Effect of reduction treatment on microstructure of CuY catalyst and its catalytic activity for oxidation carbonylation of methanol

通过还原气氛下不同温度处理CuY催化剂,改变催化剂内不同价态Cu的含量,确定甲醇氧化羰基化合成DMC的主要活性组分。以pH为9.5的Cu(NO3)2氨水溶液与NaY进行离子交换,然后在体积比为10/1的N2/H2混合气还原气氛中分别在200℃、300℃、400℃和500℃进行还原处理,制得CuY催化剂,并通过XRD、TPR和TPD对催化剂微观结构进行表征。结果表明,Cu2+的还原性能与其在Y分子筛中的落位有关,落位于分子筛超笼内的Cu2+容易被还原为Cu+,落位于小笼内的Cu2+较难还原;随还原温度的升高,Cu+和Cu0的含量都明显增加,但即使500℃还原后也存在部分未还原的Cu2+;Cu物种价态及微观结构的变化导致随还原温度升高CO吸附量降低、吸附增强和Cu0颗粒长大,这是催化剂在甲醇氧化羰基化合成DMC中催化活性随还原温度升高而下降的直接原因。

The main active components of the CuY catalyst for oxidative carbonylation of methanol to dimethyl carbonate （DMC） were determined by reducing the catalyst at different temperatures under reducing atmosphere to change the contents of Cu in different states of valence. The CuY catalysts were prepared by ion exchange of NaY with an aqueous solution of copper nitrate and ammonia at pH of 9.5, and then reduced at 200℃, 300℃, 400℃ and 500℃, respectively, under the N2/H2 mixed gas with a volume ratio of 10/1. The microstructures of the catalysts were characterized by XRD, TPR and TPD. The results showed that the reducibility of Cu2＋ related to its location in Y zeolites, and the Cu2＋ located in the supercages of zeolite was more easily reduced than that located in the smaUcages of zeolite; with the rise of reduction temperature, the contents of both Cu＋ and Cu0 significantly increased, but even if the CuY zeolites were reduced at 500℃, Cu2＋ still existed in them; and the change in microstructure and contents of different valent Cu resuhed in the decrease of CO adsorption capacity, the enhancement of CO adsorption and the growth of Cu0 particles with the rise of reduction temperature, which was the reason why the activity of the catalyst reduced with the rise of reduction temperature in the DMC synthesis reaction.