Dynamic structure of Mo-O species in Ag-Mo-P-O catalyst for oxidative dehydrogenation of propane

The dynamic structure of Mo-O species in Ag-Mo-P-O catalyst was studied by in situ confocal microprobe laser Raman spectroscopy (LRS) and catalytic test. The results indicate Mo-O species of MoO3 transformed to Mo-O species of AgMoO2PO4 in C3H8/O-2/N, (3/1/4) flow at 773 K. This behavior is closely relative to oxidative dehydrogenation of propane and intrinsic properties of Mo-O species. The Mo-O species of AgMoO2PO4 may be active species for oxidative dehydrogenation of propane

Effect of redox properties on selective oxidation of propane to acrolein over molybdate-based catalyst

The Ag-0.3 Mo0.6Ox and Ce0.1Ag0.3MoP0.6Oy catalysts were prepared and characterized by XRD, TPR, LRS, XPS and EPR techniques. And the catalytic performance of the catalysts for selective oxidation of propane to acrolein was studied. The results showed that the higher propane conversion with higher selectivity for acrolein was obtained on Ce0.1Ag0.3MoP0.6Oy catalyst, In addition, the possible intermediates, propene and propanol, were favorable for the transformation to acrolein on Ce0.1Ag0.3MoP0.6Oy catalyst. After Ce was doped in Ag0.3MoP0.6Ox, the CeO2 and Ce2MoO6 could be measured. The addition of Ce to Ag0.3MoP0.6Ox improved the reducibility and the concentration of Mo5+ owing to the formation of redox couple Mo6+ + Ce3+ === Mo5+ + Ce4+, leading to the higher propane conversion and the higher selectivity for acrolein

Dynamic structure of Mo-O species in Ag-Mo-P-O catalyst for oxidative dehydrogenation of propane

In order to understand the relationship between catalytic performance and structure of Ag-Mo-P-O caalyst for oxidative dehydrogenation of propane, the dynamic structure of Mo-O species in the catalyst was studied by in-situ confocal microprobe LRS and XRD. The catalyst was mainly Composed Of MoO3 and AgMoO2PO4 phases. The Mo-O species was monitored by in-situ confocal microprobe LRS in different atmosphere. 3C(3)H(8)-lO(2)-N-2 flow, only the Raman hands of Mo-O species in AgMoO2PO4 were detected at 773 K. In O-2 flow, the Mo-O species in MoO3 and in AgMoO2PO4 could be detected at all the investigated temperatures. In 7C(3)H(8)-43N(2) flow, the intensity of Raman bands belonging to Mo-O species in both MoO3 and AgMoO2PO4 gradually decreased and finally disappeared as temperature increasing. At that time, the catalyst was exposed to 3C(3)H(8)-lO(2)-4N(2) flow, the Raman bands belonging to Mo-O species in AgMoO2PO4 was detected. Subsequently, the catalyst was switched to O-2 flow, the Raman bands of Mo-O species in MoO3 and in AgMoO2PO4 were detected again, The results of catalytic test showed higher conversion of propane with higher selectivity for propene in 3C(3)H(8)-IO2-4N(2) flow at 773 K. The transformation of Mo-O species is due to the intrinsic properties of Mo-O species. The Mo-O species of AgMoO2PO4 might be active species for Oxidative dehydrogenation of propane

Studies on VPO/SiO2 catalyst for selective oxidation of propane

VPO catalyst is one of promising catalysts for selective oxidation of C4H10 and C3H8. The catalysts VPO and VPO/SiO2 with different VPO loading were prepared. Using BET, XRD, LRS, XPS, H-2-TPR and C3H8-TPD techniques, the physicochemical properties of the catalysts, such as structure, reducibility, vanadium oxidation states and V-O bond, as well as the interaction between C3H8 and the catalysts, were comparatively investigated. The catalytic performance of the catalysts in selective oxidation of C3H8 was also tested. VPO/SiO2 had higher specific surface area and reducibility than VPO. In addition, the binding energy of V 2p(3/2) on VPO/SiO2 was higher than that on VPO, which indicated that the coordination environment of V changed and Vdelta+ (4 < delta < 5) might exist on VPO/SiO2. Compared with VPO, the stronger interaction between C3H8 and VPO/SiO2 was observed. The interaction between Si and V occurred on VPO/SiO2, which modified its physicochemical properties and in return changed its catalytic performance. In the case of VPO/SiO2, (VO)(2)P2O7 was the main phase (oxidation state) and highly dispersed on SiO2. With the increase of VPO loading, the reduction temperature of the catalyst and binding energy of V 2p(3/2) changed slightly, and the intensity of V-O bond and the H-2 consumption in TPR increased, indicating that the amount of V-O species increased on the surface. On the other hand, with the increase of VPO loading, the C3H8 conversion increased while the CA Selectivity reduced, and the acrolein selectivity appeared the maximum value on 5% VPO/SiO2 catalyst

In-situ FT-IR study of high pressure syngas conversion over Rh/SiO2 and Rh/NaY catalysts

High pressure syngas [V(CO) : V(H-2) = 1] conversion over unpromoted Rh catalyst supported on silica and zeolite NaY were studied at 250 degreesC with an in-situ. IR cell that avoided contamination of iron carbonyls. Change of the syngas pressure produced no effect on the IR spectrum of Rh/SiO2; bridged and linear CO on Rh clusters were the only detectable surface species under 0.1 to 1.0 MPa of flowing syngas. In addition to the bridged and linear CO species, two types of dicarbonyls [Rh(I)(CO)(2)] and a small amount of Rh-6(CO)(16) were formed when Rh/NaY was exposed to 0.1 MPa syngas. Increasing of the syngas pressure to 1. 0 MPa over Rh/NaY resulted in transformation of the dicarbonyls to Rh-6(CO)(16) and probably a mononuclear medium carbonyl featuring an absorption 2042 cm(-1). The detectable reaction products adsorbed on Rh/NaY catalyst under 1.0 MPa were monodentate and bidentate acetates. These surface species were maintained even after releasing the syngas pressure back to 0.1 MPa. Thus, a remarkable difference exists in the effect of syngas pressure on the strtucture of Rh catalysts: reconstruction of Rh catalyst under high pressure of syngas occurs in zeolite NaY but not on silica. Reactivity of the adsorbed surface species toward hydrogen after the catalyst reconstruction suggests that the monodentate acetate groups are responsible for the selective formation of acetic acid from syngas over the Rh/NaY catalyst

Selective oxidation of propane to acrolein over MoPO/SiO2 catalyst

The selective oxidation of propane to acrolein over the MoPO/SiO2 catalyst has been studied. MoO/SiO2 exhibits only activity for the oxidative dehydrogenation of propane to propene. The propane conversion and acrolein selectivity are evidently increased by the addition of P to MoO/SiO2. The catalysts were characterized by XRD, Raman spectroscopy, H-2-TPR, NH3-TPD and FT-IR spectroscopy. The XRD and Raman results show that crystalline MoO3 is dominant on the silica-supported molybdenum oxide catalyst, while polymolybdate species are present on P-doped catalysts. Compared to the P-O-P stretching vibration at 905 cm(-1) in PO/SiO2, the P-doped sample exhibits the Raman band of the asymmetric PO4 stretching mode at 1085 cm(-1). Therefore, Mo-O-P bonds are likely to be formed on the P-doped catalyst, and the active sites are isolated by the phosphorus in MOPO/SiO2, preventing the growth of crystallized MoO3. These changes in structure and thus the improvement in reducibility of the MoPO/SiO2 catalyst may be responsible for the increase in propane conversion and acrolein selectivity. Furthermore, the results of FT-IR spectroscopy of pyridine adsorption and NH3-TPD show that both Bronsted and Lewis acid sites on the surface of the P-doped sample are stronger than those on MoO/SiO2. These suggest that the addition of phosphorus modifies the surface structure and enhances the surface acidity of the supported catalyst, thus improving the behavior of the catalyst

Preparation of nanoscale ytterbia by wet chemical methods

Several wet chemical methods, such as conventional precipitation, microemulsion route and homogeneous precipitation, have been used to prepare nanosized ytterbium oxides. After being calcined at 650 degreesC, well-dispersed spherical particles with size of about 10 nm characterized by TEM observations can be prepared by hydrogen peroxide- or CTAB-aided precipitation process. XRD results show that the as-prepared samples are cubic ytterbium oxides with the crystal sizes of 9.4 nm for hydrogen peroxide-aided way and 6.9 nm for CTAB-containing route. Nitrogen adsorption characterization at 77 K indicates that (i) the present microemulsion process gives a sample with the lowest specific surface area compared with other methods, (ii) ytterbium oxides with specific surface areas of 47.7 m(2)/g (equivalent diameter of 13.6 nm) and 63.2 m(2)/g (equivalent diameter of 10.3 nm) can be prepared by hydrogen peroxide-aided way and CTAB-containing homogeneous precipitation process, respectively. The interaction between the surfactants and the hydrous ytterbia may play an important role in the thermal stability of the derived Yb2O3

Low-temperature catalytic performance of nanostructured Ti-Ni-O prepared by modified sol-gel method

Nanosized Ti-Ni-O catalysts prepared by a modified sol-gel method had been investigated in the oxidative dehydrogenation of ethane and propane to the corresponding alkene. The best yield is obtained over the 9.1wt% Ti-Ni-O catalyst. The results of catalyst characterization indicated that there is strong interaction between TiO2 and NiO. It is observed that a decline in temperature for low-temperature oxygen desorption and an augmentation in reduction difficulty of the catalysts would result in poor activity and enhanced alkene selectivity, respectively, over the Ti-Ni-O catalysts in the oxidative dehydrogenation reactions