Studies On Catalytic Performance Of Mesoporous Carbon Materials-supported Copper Catalysts For Oxidative Carbonylation Of Methanol

Activated carbon supported copper catalyst Cu/AC exhibits prominent catalytic activity for oxidative carbonylation of methanol to DMC. However, 95.3% of the surface area of AC was occupied with disordered micropores and the rest were irregular mesoporous or macro porous and the Cu particles of Cu/AC catalysts were generally located outside the pores of AC, resulting to inadequate utilization of the large surface area of AC, slow diffusion kinetics and restriction of mass transfer. Mesoporous carbon material with highly ordered mesoporous structure, uniform interface chemical properties, well-de?ned and narrow pore size distribution may efficiently disperse the active copper particles in its mesopores, which is promising to increase the untilization of its surface area, improving the catalytic activity. Ordered mesoporous carbon（OMC） and mesoporous carbon spheres are new mesoporous carbon materials with developed mesoporous structure, uniform pore size distribution and thus widely applied in catalysis area.OMC and mesoporous carbon sphere supported chloride-free catalysts were prepared and applied for oxidative carbonylation of methanol to DMC to investigate the pore structure influence on copper dispersion, location and corresponding state.The contents and main conclusions are listed below:（1） To investigate the structure influence of the two OMC supports on the catalytic performance for methanol oxidative carbonylation to DMC, HOMC and SOMC with similar mesoporous diameter and surface properties were prepared and used as supports of Cu catalysts. Both OMC materials have highly ordered mesoporous structure and large external specific surface area as well as mesoporous confinement effects, which are beneficial to the dispersion of active Cu species. The pore structure of SOMC is constituted by well-de?ned long hollow interiors 3.6 nm in diameter connected by pore walls, and most Cu particles with diameter of 4.5-6 nm or larger were located on the outer surface of SOMC framework. While that of HOMC is made up of ordered arrays of carbon nanorods, and the mesopores of HOMC with average pore size of 3.6 nm are the interconnected spaces among the carbon nanorods.（2） Combining with the adjustment of Cu loading, the structure effects of the support on the Cu location and Cu dispersion are compared. The pore structure distinction of the two OMC materials has remarkable influences on Cu dispersion, Cu location, Cu valence as well as the corresponding content. As mentioned above, most Cu particles of Cu/SOMC catalysts were located on the outer surface of SOMC framework. These large Cu particles supported on the surface of SOMC were detrimental to their autoreduction from Cu O to Cu2 O, especially for the high copper loading Cu/SOMC. By contrast, most of Cu particles of Cu/HOMC were homogeneously con?ned and distributed inside the mesoporous of HOMC, these highly dispersed ultrafine Cu particles on the surface of HOMC support are beneficial to their self-reduction from CuO to Cu2 O, even when increasing the copper loading.（3） As for the catalytic property, Cu/HOMC catalysts performed better in terms of the methanol conversion and DMC space-time yield derive from better copper dispersion and more active species, whilst Cu/SOMC catalysts exhibited better stability due to the presence of large Cu particles and CuO species. Besides, appropriately increasing the copper loading of the Cu catalyst can increase both the methanol conversion and DMC selectivity and is considered as a good option to improve the space-time yield of DMC.（4） Solid carbon spheres SCS with outer-diameter of 400-900 nm, specific area of 517m²g^-1 were prepared by hydrothermal method, and hollow mesoporous carbon HCS^-1 with outer-size of 450 nm and inner diameter of 100 nm and HCS-2 with outer-size of 200 nm and inner diameter of 65 nm were synthesized successfully through adding oleic acid.（5） Cu@SCS, Cu@HCS^-1 and Cu@HCS-2 catalysts were successfully synthesized by incipient impregnation. For Cu@SCS, copper particles were mainly located in the outer surface and its average particle size is 9.9 nm, and 3.5 nm copper particles of Cu@HCS^-1 primarily highly-dispersed in the shell mesopores, while those for Cu@HCS-2 were located in the cores of the mesoporous carbon with diameter of 8.5 nm. Cu@HCS^-1 porformed better STYDMC of 129.7 mg·g^-1cat·h^-1 comparing with Cu@HCS-2 and Cu@SCS with STYDMC of 120.8 mg·g^-1cat·h^-1 and 54.6 mg·g^-1cat·h^-1, respectively.（6） Ultrasonic wave was introduced when preparing Cu@HCS-2 to further disperse copper particles in the shell mesopores of Cu@HCS-2-u and the average diameter of copper particles is only 2.0 nm. When the inner HCS-2 was filled with normal octane, 13.7 nm copper particles of Cu@HCS-2-n were located outside the HCS-2. STYDMC of Cu@HCS-2-u is 196.6 mg·g^-1cat·h^-1, which is 1.63 times of that of the Cu@HCS^-1. By contrast, STYDMC for Cu@HCS-2-n is only 21.5 mg·g^-1cat·h^-1.