The ammoxidation of substituted toluenes to their corresponding nitriles over silica-supported vanadium phosphorus oxide (VPO/SiO2) catalysts has been studied. the effects of carrier silica, the addition of phosphorus...The ammoxidation of substituted toluenes to their corresponding nitriles over silica-supported vanadium phosphorus oxide (VPO/SiO2) catalysts has been studied. the effects of carrier silica, the addition of phosphorus, the substituents and the loadings have been discussed. Compared with unsupported VPO, the VPO/SiO2 catalysts have higher catalytic activity for ammoxidation of substituted toluenes and much lower reaction temperature. XRD shows that vanadium phosphorus oxides exist as amorphous phase and disperse to a high degree on the silica surface in 10%loading catalyst. When the loadings are over 10%, the crystalline α-VOPO4 would emerge, which would decrease the yield and selectivity. Additional phosphorus can form composite oxides with vanadia and play concerted catalytic function, which increase the selectivity of nitriles remarkably. Different substituents or same substituents on different positions have different influences because of the variant electronic stability of intermediates, the hindered accessibility of methyl group or the chemisorption state of the substrate molecule on the electrophilic catalyst surface.展开更多
The water acidity has significant influences on the structures of both catalytic precursors and catalysts as well as catalytic performances. If the pH of water is higher than or equal to 3.0, the precursors contain pu...The water acidity has significant influences on the structures of both catalytic precursors and catalysts as well as catalytic performances. If the pH of water is higher than or equal to 3.0, the precursors contain pure (VO) 2P 2O 7·2H 2O and activated catalysts have (VO) 2P 2O 7 and β VOPO 4. When the pH of the water is lower than 3.0, the precursors are made up of (VO) 2P 2O 7·2H 2O and (VO) 2P 2O 7·4H 2O and the activated catalysts consist of (VO) 2P 2O 7 as well as α VOPO 4. Among the catalysts which had experienced water treatment, the catalyst has the best selectivity and highest mass yield to maleic anhydride when pH is 3.0. But all the catalysts show a similar activity for butane oxidation regardless of the pH. Furthermore, the more the (VO) 2P 2O 7·4H 2O in the catalyst, the lower the selectivity and mass yield to maleic anhydride. The (VO) 2P 2O 7·4H 2O in the precursor can be eliminated by controlling the water treatment with pH≥3.0 to ensure the catalyst having excellent behavior.展开更多
VPO are well-known catalysts for the oxidation of n-butane to maleic anhydride. The catalytic behavior is influenced by several factors, such as the phase composition and the vanadium oxidation state of VPO catalysts....VPO are well-known catalysts for the oxidation of n-butane to maleic anhydride. The catalytic behavior is influenced by several factors, such as the phase composition and the vanadium oxidation state of VPO catalysts. These catalysts have been characterized by means of XRD and XPS, but it is difficult to detect the presence of low concentrations of VOPO<sub>4</sub> phases展开更多
VPO polymer β NH 4(VO 2)(HPO 4) was synthesized from the mixture of NH 4VO 3 and NH 4H 2PO 4 in aqueous acidic solution. This hydrogenphosphate vanadate crystallizes in the orthorhombic space group Pbca with a=0.680 ...VPO polymer β NH 4(VO 2)(HPO 4) was synthesized from the mixture of NH 4VO 3 and NH 4H 2PO 4 in aqueous acidic solution. This hydrogenphosphate vanadate crystallizes in the orthorhombic space group Pbca with a=0.680 60(8) nm, b=0.925 70(5) nm, c=1.773 70(2) nm, V=1.117 5(3) nm 3, Z=8, D c=1.743 g·cm -3 , μ=88.54 cm -1 and R=0.051. The structure is built up from VO 5 square pyramid linked by trans vertices through the bridged oxygen atom to form an one dimensional isolated chain of {VO 2HPO 4} n- nunning along the a axis.展开更多
Phase composition, surface characterization and catalytic performance of VPO and thulium doped VPO catalysts were investigated by means of NH3-TPD, XPS,XRD and IR. Experimental results showed that when Tm/V (atomic ra...Phase composition, surface characterization and catalytic performance of VPO and thulium doped VPO catalysts were investigated by means of NH3-TPD, XPS,XRD and IR. Experimental results showed that when Tm/V (atomic ratio) ＜0.10, both Bronsted and Lewis acidities on the surface of VPO catalysts with the addition of thulium were stronger than those of VPO catalyst, the doped catalyst accelerated the dehydrogena tion step of the oxidation reaction of n-butane. Conversion of n-butane and selectivity to maleic anhydride were enhanced. While Tm/V■0.10, the surface acidity of the catalysts was decreased and the activity of catalysts was dropped.展开更多
文摘The ammoxidation of substituted toluenes to their corresponding nitriles over silica-supported vanadium phosphorus oxide (VPO/SiO2) catalysts has been studied. the effects of carrier silica, the addition of phosphorus, the substituents and the loadings have been discussed. Compared with unsupported VPO, the VPO/SiO2 catalysts have higher catalytic activity for ammoxidation of substituted toluenes and much lower reaction temperature. XRD shows that vanadium phosphorus oxides exist as amorphous phase and disperse to a high degree on the silica surface in 10%loading catalyst. When the loadings are over 10%, the crystalline α-VOPO4 would emerge, which would decrease the yield and selectivity. Additional phosphorus can form composite oxides with vanadia and play concerted catalytic function, which increase the selectivity of nitriles remarkably. Different substituents or same substituents on different positions have different influences because of the variant electronic stability of intermediates, the hindered accessibility of methyl group or the chemisorption state of the substrate molecule on the electrophilic catalyst surface.
文摘The water acidity has significant influences on the structures of both catalytic precursors and catalysts as well as catalytic performances. If the pH of water is higher than or equal to 3.0, the precursors contain pure (VO) 2P 2O 7·2H 2O and activated catalysts have (VO) 2P 2O 7 and β VOPO 4. When the pH of the water is lower than 3.0, the precursors are made up of (VO) 2P 2O 7·2H 2O and (VO) 2P 2O 7·4H 2O and the activated catalysts consist of (VO) 2P 2O 7 as well as α VOPO 4. Among the catalysts which had experienced water treatment, the catalyst has the best selectivity and highest mass yield to maleic anhydride when pH is 3.0. But all the catalysts show a similar activity for butane oxidation regardless of the pH. Furthermore, the more the (VO) 2P 2O 7·4H 2O in the catalyst, the lower the selectivity and mass yield to maleic anhydride. The (VO) 2P 2O 7·4H 2O in the precursor can be eliminated by controlling the water treatment with pH≥3.0 to ensure the catalyst having excellent behavior.
文摘VPO are well-known catalysts for the oxidation of n-butane to maleic anhydride. The catalytic behavior is influenced by several factors, such as the phase composition and the vanadium oxidation state of VPO catalysts. These catalysts have been characterized by means of XRD and XPS, but it is difficult to detect the presence of low concentrations of VOPO<sub>4</sub> phases
文摘VPO polymer β NH 4(VO 2)(HPO 4) was synthesized from the mixture of NH 4VO 3 and NH 4H 2PO 4 in aqueous acidic solution. This hydrogenphosphate vanadate crystallizes in the orthorhombic space group Pbca with a=0.680 60(8) nm, b=0.925 70(5) nm, c=1.773 70(2) nm, V=1.117 5(3) nm 3, Z=8, D c=1.743 g·cm -3 , μ=88.54 cm -1 and R=0.051. The structure is built up from VO 5 square pyramid linked by trans vertices through the bridged oxygen atom to form an one dimensional isolated chain of {VO 2HPO 4} n- nunning along the a axis.
文摘Phase composition, surface characterization and catalytic performance of VPO and thulium doped VPO catalysts were investigated by means of NH3-TPD, XPS,XRD and IR. Experimental results showed that when Tm/V (atomic ratio) ＜0.10, both Bronsted and Lewis acidities on the surface of VPO catalysts with the addition of thulium were stronger than those of VPO catalyst, the doped catalyst accelerated the dehydrogena tion step of the oxidation reaction of n-butane. Conversion of n-butane and selectivity to maleic anhydride were enhanced. While Tm/V■0.10, the surface acidity of the catalysts was decreased and the activity of catalysts was dropped.
