Catalytic Oxidation Of N-butane Research Articles

Synthesis of self-assembled nanorod vanadium oxide bundles by sonochemical treatment

Self-assembled nanorod of vanadium oxide bundles were synthesized by treating bulk V 2O 5 with high intensity sonochemical technique. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and temperature-programmed reduction (TPR) in H 2. Catalytic behaviour of the materials over anaerobic n-butane oxidation was studied through temperature-programmed reaction (TPRn). Catalytic evaluation of the sonochemical treated V 2O 5 products was also studied on microreactor. XRD patterns of all the vanadium samples were perfectly indexed to V 2O 5. The morphologies of the nanorod vanadium oxides as shown in SEM and TEM depended on the duration of the ultrasound irradiation. Prolonging the ultrasound irradiation duration resulted in materials with uniform, well defined shapes and surface structures and smaller size of nanorod vanadium oxide bundles. H 2-TPR profiles showed that larger amount of oxygen species were removed from the nanorod V 2O 5 compared to the bulk. Furthermore, the nanorod vanadium oxide bundles, which were produced after 90, 120 and 180 min of sonochemical treatment, showed an additional reduction peak at lower temperature (∼850 K), suggesting the presence of some highly active oxygen species. TPRn in n-butane/He over these materials showed that the nanorod V 2O 5 with highly active oxygen species showed markedly higher activity than the bulk material, which was further proven by catalytic oxidation of n-butane.

Cluster-Based Modeling of Fluidized Catalytic Oxidation of n-Butane to Maleic Anhydride

A mathematical model is proposed for the partial oxidation on n-butane to maleic anhydride (MAN) in a gas-solid fluidized bed reactor. The reactor consists of two regions, i.e., a lower dense region and an upper dilute region. The dynamic two-phase structure was used for modeling the lower dense bed hydrodynamics. The upper region hydrodynamics was modeled by a cluster based approach. This allows the porosity distribution to be calculated for plug flow reactor model assumed for the gas phase in this region. The basic assumption in the cluster based approach is that the solid particles move only as clusters and the amount of single particles in the upper region is negligible. The mathematical model was obtained from coupling the kinetic sub-model, obtained from the literature, with this hydrodynamics sub-model. Comparing the results of the model with the experimental data available in the literature showed close agreement. Two other methods (i.e., particle based approach and short-cut) were also tested in this work. However, it was found that the cluster based approach modeling is quite suitable for the fluidized bed reactor used in this study. The short-cut method seems reasonably applicable for the prediction of the overall conversion but does not provide any local information (such as concentration profiles, yield, etc.) within the fluidized bed reactor.

Characteristic features of Raman band shifts of vanadium oxide catalysts exchanged with the [formula omitted] tracer and active sites for reoxidation

The oxide oxygen ions of V 2O 5 catalyst were exchanged with 18 O tracer by a reduction–oxidation method and by a catalytic oxidation of n-butane using 18 O 2. The Raman band shifts of the V 2O 5 exchanged with 18 O by the methods were examined. The band at 700 cm −1 was shifted to lower frequencies more preferentially than the band of VO oxygen at 998 cm −1. Applying the correlation between the Raman bands and stretching modes as described in the literature, the positions of oxide ions and anion vacancies for reduction and reoxidation were estimated. The anion vacancies corresponding to the V–O species in the V square with 1.88 and 2.02 Å distances seem to be active sites for oxygen insertion. The similar conclusions were obtained for Mo containing V 2O 5 catalyst.

Anisotropic oxidation of crystallites of vanadyl pyrophosphate

Anisotropic oxidation of crystallites of vanadyl pyrophosphate ((VO)2P2O7) has been demonstrated by Raman spectroscopy with samples having different microstructures. Oxidation of these samples by O2 produced X1 phase,α- andβ-VOPO4 phases. The relative peak intensity of the X1 phase to the other phases correlated well with the ratio of the (100) plane to the side planes (surface area-basis). This correlation showed that the (100) plane was oxidized to X1 phase and the side planes toα- andβ-VOPO4. For example, thin plate-like (VO)2P2O7, of which the (100) fraction is 98%, was oxidized almost exclusively to X1 phase. But when it was fractured into small plates to increase the side planes and then oxidized,α- andβ-VOPO4 were detected in addition to the X1 phase. These results are consistent with our previous conclusion that the (100) plane of (VO)2P2O7 is selective, but side planes are non-selective for catalytic oxidation ofn-butane.

Redox processes of surface of vanadyl pyrophosphate in relation to selective oxidation ofn-butane

Oxidation and reduction processes of the surface of vanadyl pyrophosphate ((VO)2P2O7) have been studied by means of Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry, and “micro-pulse” reaction ofn-butane in relation to the selective oxidation ofn-butane. Oxidation of (VO)2P2O7 by O2 was carried out to controlled extents by changing the reaction temperature and period. When (VO)2P2O7 was oxidized at 733 K for 2 h, about one layer of the surface of (VO)2P2O7 was oxidized to the X1 phase, which was reported previously by the authors, as deduced from the amount of O2-uptake and spectroscopic changes. Reductions of the surface X1 phase and β-VOPO4 were carried out by a “micro-pulse” reaction with n-butane at 733 K. The reduction byn-butane changed the surface X1 phase to (VO)2P2O7 and, at the same time, gave maleic anhydride with selectivities ranging from 13 to 40%. The selectivity was less than 10% in the case of β-VO)2PO4. These results suggest that the redox cycle between the X1 phase and (VO)2P2O7 in the surface layer is involved in the catalytic oxidation ofn-butane to maleic anhydride.

Spectroscopic Study of the Vanadium-Phosphate Catalyst Used in the Selective Oxidation of n-Butane to Maleic Anhydride

UV—VIS and electron spin resonance spectra were used to investigate the electronic structure of the vanadium—phosphate catalyst used in the selective oxidation of n-butane to maleic anhydride during its preparation as well as in the course of its interaction with oxygen and n-butane or with a mixture of these two substances. V 3+ and V 4+ were identified in the catalyst. It has been shown that V 3+ ions can act as electron donor (via the transition V 3+ → V 4+) during the adsorption of oxygen and thus participate in the catalytic oxidation of n-butane.

ChemInform Abstract: Selective Oxidation of Lower Alkanes over Oxide Catalysts

The selective oxidation of alkanes to alkenes, alkadienes, and oxygen-containing products is of great industrial importance. In this review, recent progress in the selective oxidations of C1-C4 alkanes over oxide catalysts has been described.Typical examples reported recently for oxidation of CH4 to C2H6, C2H4, HCHO and CH3OH are summarized in Table 1 and those for C2H6 and C3H8 are in Table 2. The catalytic oxidation of n-butane to maleic anhydride which has been industrialized by using V-P mixed oxide catalysts has been reviewed in more detail. V-P mixed oxide having P/V ratio of 1 - 1.2 have often been claimed as active catalysts. Hovever, by comparing the catalysis of crystalline phases with P/V = 1 (α-, β-VOPO4, etc.), it has been indicated that crystalline (VO) 2P2O7 is the effective phase. Its structural and redox characteristics are discussed based on the recent literature.

Structure sensitivity of the catalytic oxidation of n-butane to maleic anhydride

Disorder along the (020) cleavage plane of the (VO)2P2O7 catalyst considerably enhances the activity of the selective oxidation of n-butane to maleic anhydride.