Construction of highly dispersed active copper species on Y molecular sieve and performance of methanol oxidation carbonylation
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摘要: 本研究采用溶液离子交换法制备了不同载量的CuY催化剂,结合XRD、TEM、H2-TPR、XPS、NH3-TPD和CH3OH-TPD等分析CuY微观结构,探讨了铜氨溶液浓度及活化温度对CuY表面铜物种状态及性能的影响。发现增大交换溶液浓度虽会降低催化剂孔隙率,但能将铜载量由2.11%显著提升至9.95%,并仍保持着铜物种的高分散,铜粒径不足4 nm。溶液交换会破坏表面酸结构而减少表面弱酸位,抑制副反应进而提高DMC选择性。低载量催化剂铜物种以离子态铜为主,增加铜含量提升离子态铜含量的同时,也显著增加了CuOx,能使催化性能迅速提高,甲醇转化率和DMC收率分别达到9.07%和396.27 mg/(g·h)。控制催化剂活化温度研究铜物种活化过程发现,适宜温度的活化会促进表面铜物种向分子筛内部孔道的扩散和交换,并减弱甲醇的吸附强度,利于性能的提升。高载量催化剂相比低载量催化剂能在低温下活化获得更多的Cu+和CuOx而表现出高催化活性。本工作研究结果为高性能CuY催化剂的设计和制备提供了理论基础。Abstract: The control of copper species on the surface of CuY catalyst is the key to improve the performance of methanol oxidation carbonylation to dimethyl carbonate. In this work, a series of CuY catalysts with different copper loads were prepared by solution ion exchange method, and the N2-physisorption, XRD, TEM, H2-TPR, XPS, NH3-TPD and CH3OH-TPD were used to characterize the microstructure of the catalyst. The effects of Cu-ammonia solution concentration and activation temperature for structure and properties of CuY surface copper were investigated. The results indicated that although the porosity of the catalyst was reduced by increasing the concentration of solution, the amount of copper was significantly increased from 2.11% to 9.95%, and the high dispersion of copper species was maintained, with the particle size less than 4 nm. The high concentration of solution exchange reduced the weak acid sites on the surface and inhibited side reactions to improve the selectivity of DMC. The copper species of low loading catalysts were mainly ionic copper. Increasing the content of copper increased the content of ionic copper, but also significantly increases the amount of CuOx, which could rapidly improve the catalytic performance, methanol conversion and DMC yield reached 9.07% and 396.27 mg/(g·h), respectively. The activation at suitable temperature promoted the diffusion of copper species from the external surface to the internal pores, increasing the exchange of Cu species with NaY and weakening the adsorption strength of methanol, which was conducive to the improvement of catalytic performance. Compared with low loading catalysts, high loading catalysts could be activated to obtain more Cu+ and CuOx at low temperature, thus showing higher catalytic performance. The results of this work provided a theoretical basis for the design and preparation of high-performance CuY catalysts.
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Key words:
- oxidative carbonylation /
- Cu catalyst /
- zeolite /
- catalytic perform
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表 1 不同浓度交换溶液制备的CuY催化剂的活性
Table 1 Activity of CuY catalysts prepared with different exchange solutions
Sample Cu content/
%$x_{{\rm{CH}}_3{\rm{OH}}} $/
%sDMC/
%STYDMC/
(mg·g−1·h−1)Y-0.02 2.11 1.03 48.56 33.69 Y-0.04 4.44 2.52 60.93 103.66 Y-0.06 7.48 6.61 64.16 286.21 Y-0.08 7.86 7.66 64.94 335.76 Y-0.10 8.59 9.07 64.66 396.27 Y-0.12 9.95 9.02 64.84 394.47 表 2 不同催化剂的活性及织构性质
Table 2 The reactivities and texture properties of different catalysts
Sample $x_{ {\rm{CH} }_3{\rm{OH} } } $/
%sDMC/
%STYDMC/
(mg·g−1·h−1)SBET/
(m2·g−1)daverage/
nmvtotal/
(cm3·g−1)Y − − − 744 1.94 0.37 Y0.04-200 0.77 41.42 21.91 647 2.19 0.35 Y0.04-400 1.11 30.29 22.63 650 2.20 0.35 Y0.04-600 2.18 64.45 94.76 651 2.12 0.35 Y0.04-800 0.03 0 0 1.53 37.66 0.01 Y0.10-200 1.40 75.41 72.35 583 2.23 0.33 Y0.10-400 8.23 66.33 368.92 606 2.18 0.33 Y0.10-600 8.82 67.42 401.52 655 2.09 0.34 Y0.10-800 0.88 0 0 0.41 94.70 0.01 -
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