Selective hydrogenation of cinnamaldehyde over Pt-supported multi-walled carbon nanotubes: Insights into the tube-size effects
Selective hydrogenation of cinnamaldehyde over Pt-supported multi-walled carbon nanotubes: Insights into the tube-size effects
复制标题
DOI：
10.1016/j.apcata.2008.04.005
复制
发表时间：
2008-07
影响因子：
5.5
通讯作者：
Zhaoqing Liu;Chunxiang Wang;Zhongwen Liu;Jian Lu
中科院分区：
文献类型：
--
作者：
Zhaoqing Liu;Chunxiang Wang;Zhongwen Liu;Jian Lu
在乙醇和水溶液中，通过甲醛还原H_2PtCl6，制备了外径不同但内径相近的多壁碳纳米管(MWCNTs)，负载了3.0wt.%的铂。对于MWCNT载体和催化剂，由氮气吸附和脱附确定的BET比表面积和孔径分布有很大的不同，但观察到具有闭合滞后环的II型吸附等温线。在间歇反应器中考察了3.0wt.%Pt/MWCNT催化剂在80℃、2.0 Mpa氢气条件下对肉桂醛(CALD)的选择性加氢反应。所有催化剂均表现出较高的催化活性，但产物选择性差异较大。在外径最大(>；50 nm)的铂负载的MWCNT4催化剂上，CC键高选择性加氢成对氢肉桂醛，选择性为88%，转化率为100%。然而，在其他三种催化剂中，CO键被选择性氢化，根据催化剂和CALD转化率的不同，对肉桂醇(CA)的选择性约为60%-80%。X-射线衍射仪和高分辨电子显微镜的结果表明，无论催化剂是什么，金属铂颗粒的平均尺寸约为11 nm，绝大多数沉积在多壁碳纳米管的外表面。X射线光电子能谱测定不同催化剂的铂结合能和表面氧碳原子比略有不同。根据这些表征结果，结合CA的加氢反应结果，讨论了铂/多壁碳纳米管催化剂的不同选择行为。除了其他因素外，MWCNTs管径的显著变化所产生的电子效应在决定不同催化剂的选择行为中起主要作用。
The multi-walled carbon nanotubes (MWCNTs) having different outer diameters but similar inner diameters were loaded with 3.0wt.% Pt via the reduction of H2PtCl6by formaldehyde in the solution of ethanol and water. For both the MWCNT supports and catalysts, the BET surface areas and pore size distributions determined by N2adsorption and desorption were varied significantly although type II adsorption isotherms with closed hysteresis loops were observed. The 3.0wt.% Pt/MWCNT catalysts were investigated for the selective hydrogenation of cinnamaldehyde (CALD) in a batch reactor under the conditions of 80°C and 2.0MPa of hydrogen. All the catalysts showed reasonably high catalytic activity but significantly different product selectivities. The highly selective hydrogenation of CC bonds into hydrocinnamaldehyde (88% selectivity at 100% conversion) occurred over Pt-supported MWCNT4 with the biggest outer diameters (>50nm). In the case of the other three catalysts, however, CO bonds were selectively hydrogenated showing about 60–80% selectivities to cinnamyl alcohol (CA) depending on the catalysts and CALD conversions. Irrespective of the catalysts, the results of X-ray diffraction and high-resolution transmission electron microscopy indicated that the metallic Pt particles with an average size of about 11nm were overwhelmingly deposited on the outer surface of the MWCNTs. The binding energies of Pt and the surface atomic ratios of oxygen to carbon determined by X-ray photoelectron spectroscopy were slightly varied for different catalysts. Based on these characterization results together with the hydrogenation results of CA, the different selective behaviors of the Pt/MWCNTs catalysts were discussed. Besides other factors, the electronic effects induced by the significantly varied tube diameters of the MWCNTs played the major role in determining the selective behaviors of different catalysts.