The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina（AA） supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight...The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina（AA） supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight tested catalysts. The catalyst was prepared by loading KH2PO4 on AA and then calcining at the optimized temperature of 700 °C for 8 h. In the vapor phase reaction, the level of anisole yield（LAY） has a maximum at 400–450 °C when the temperature varied from 300 to 500°C, which decreased slightly with increasing WHSV and increased distinctly with increasing mole fraction of methanol. On comparing O‐methylation and C‐methylation of phenol, a low temperature,high WHSV（short residence time）, and a low methanol concentration over the KH2PO4/AA catalyst with higher K contents were found to increase anisole selectivity by O‐methylation of phenol. The reaction routes to the major products and the catalytic mechanism were suggested, and a ‘K‐acid＇bifunctional process may be a critical factor to the formation of anisole.展开更多
The cleavage of the alkoxy(Ar-O-R) ether bond present in anisole is an interesting hydrodeoxygenation(HDO) reaction, since this asymmetric group contains two different C–O bonds, Caryl–O or Calkyl–O, which could po...The cleavage of the alkoxy(Ar-O-R) ether bond present in anisole is an interesting hydrodeoxygenation(HDO) reaction, since this asymmetric group contains two different C–O bonds, Caryl–O or Calkyl–O, which could potentially cleave. Recent work on the HDO of anisole over Pt, Ru, and Fe catalysts has shown that a common phenoxy surface intermediate is formed on all three metals. The subsequent reaction path of this intermediate varies from metal to metal, depending on the metal oxophilicity. Over the less oxophilic Pt, phenol is the only primary product. By contrast, on the more oxophilic Fe catalyst, the sole primary product is benzene instead of phenol. On Ru, with intermediate oxophilicity, both benzene and phenol are primary products. In this contribution, we have investigated Rh catalysts of varying surface nanostructures. A combination of experimental measurements and computational calculations was used to explore the effects of varying metal coordination number, an additional parameter that can be used to control the oxophilicity of a metal. The results confirm that metal oxophilicity is a good descriptor for HDO performance of metal catalysts and it can be controlled via selection of metal type and/or metal extent of coordination. Small Rh metal clusters with low coordination metal sites are more active for the deoxygenation pathway but also quickly deactivated while large clusters with high coordination sites are more active toward hydrogenation and more stable.展开更多
为了有效地检测和监测葡萄酒中的木塞污染物,更好把控葡萄酒的品质,建立了自动顶空-固相微萃取-气相色谱三重四级杆质谱(Automatic headspace-solid phase microextraction combined with gas chromatography-triple quadrupole mass sp...为了有效地检测和监测葡萄酒中的木塞污染物,更好把控葡萄酒的品质,建立了自动顶空-固相微萃取-气相色谱三重四级杆质谱(Automatic headspace-solid phase microextraction combined with gas chromatography-triple quadrupole mass spectrometry,Auto-HS-SPME-GC-MS/MS)检测葡萄酒中9种卤代苯甲醚和卤代苯酚类木塞污染物的方法。实验中,卤代苯酚类化合物与乙酸酐发生在线衍生化反应得到乙酰化产物,卤代苯甲醚和卤代苯酚乙酰化产物再通过HS-SPME浓缩富集后经GC-MS/MS检测,同位素内标法定量。通过优化自动固相微萃取的实验条件,对葡萄酒和起泡酒的样品进行了测定。结果表明,方法线性范围为3~300 ng/L,相关系数R^(2)为0.9988~0.9999,线性关系良好。方法检出限为1 ng/L,9种目标物加标回收率在63.7%~118.4%之间,具有较好的准确度;相对标准偏差为2.0%~16.4%,说明实验方法及仪器具有良好的精密度。该方法自动化程度高且可靠稳定,适用于葡萄酒中卤代苯甲醚、卤代苯酚类化合物的痕量检测。展开更多
基金supported by the National Natural Science Foundation of China(51476180)the National Basic Research Program of China(973Program2014CB744304)~~
文摘The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina（AA） supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight tested catalysts. The catalyst was prepared by loading KH2PO4 on AA and then calcining at the optimized temperature of 700 °C for 8 h. In the vapor phase reaction, the level of anisole yield（LAY） has a maximum at 400–450 °C when the temperature varied from 300 to 500°C, which decreased slightly with increasing WHSV and increased distinctly with increasing mole fraction of methanol. On comparing O‐methylation and C‐methylation of phenol, a low temperature,high WHSV（short residence time）, and a low methanol concentration over the KH2PO4/AA catalyst with higher K contents were found to increase anisole selectivity by O‐methylation of phenol. The reaction routes to the major products and the catalytic mechanism were suggested, and a ‘K‐acid＇bifunctional process may be a critical factor to the formation of anisole.
基金supported by the U.S.Department of Energy,DOE/EPSCOR(Grant DESC0004600)
文摘The cleavage of the alkoxy(Ar-O-R) ether bond present in anisole is an interesting hydrodeoxygenation(HDO) reaction, since this asymmetric group contains two different C–O bonds, Caryl–O or Calkyl–O, which could potentially cleave. Recent work on the HDO of anisole over Pt, Ru, and Fe catalysts has shown that a common phenoxy surface intermediate is formed on all three metals. The subsequent reaction path of this intermediate varies from metal to metal, depending on the metal oxophilicity. Over the less oxophilic Pt, phenol is the only primary product. By contrast, on the more oxophilic Fe catalyst, the sole primary product is benzene instead of phenol. On Ru, with intermediate oxophilicity, both benzene and phenol are primary products. In this contribution, we have investigated Rh catalysts of varying surface nanostructures. A combination of experimental measurements and computational calculations was used to explore the effects of varying metal coordination number, an additional parameter that can be used to control the oxophilicity of a metal. The results confirm that metal oxophilicity is a good descriptor for HDO performance of metal catalysts and it can be controlled via selection of metal type and/or metal extent of coordination. Small Rh metal clusters with low coordination metal sites are more active for the deoxygenation pathway but also quickly deactivated while large clusters with high coordination sites are more active toward hydrogenation and more stable.
文摘为了有效地检测和监测葡萄酒中的木塞污染物,更好把控葡萄酒的品质,建立了自动顶空-固相微萃取-气相色谱三重四级杆质谱(Automatic headspace-solid phase microextraction combined with gas chromatography-triple quadrupole mass spectrometry,Auto-HS-SPME-GC-MS/MS)检测葡萄酒中9种卤代苯甲醚和卤代苯酚类木塞污染物的方法。实验中,卤代苯酚类化合物与乙酸酐发生在线衍生化反应得到乙酰化产物,卤代苯甲醚和卤代苯酚乙酰化产物再通过HS-SPME浓缩富集后经GC-MS/MS检测,同位素内标法定量。通过优化自动固相微萃取的实验条件,对葡萄酒和起泡酒的样品进行了测定。结果表明,方法线性范围为3~300 ng/L,相关系数R^(2)为0.9988~0.9999,线性关系良好。方法检出限为1 ng/L,9种目标物加标回收率在63.7%~118.4%之间,具有较好的准确度;相对标准偏差为2.0%~16.4%,说明实验方法及仪器具有良好的精密度。该方法自动化程度高且可靠稳定,适用于葡萄酒中卤代苯甲醚、卤代苯酚类化合物的痕量检测。
