Industrial catalysts used in commercial processes for the production of maleic anhydride are mainly Vanadium Phosphorous Oxide (VPO) catalysts. The VPO catalyst used is Vanadyl Pyrophosphate (VO)2P207 made from its precursor Vanadium Phosphorous Hemi-Hydrate VOHP04.O.5H20 in an non-aqueous medium. In order for the VPO catalyst to perform optimally, a metal promoter, Ru, was selected as the doping agent in this study. Four catalysts of different metal doping concentrations (undoped, 0.2%, 0.6% and 1%) were subjected to the oxidation of n-butane. Promoters are added to facilitate the oxidation of n-butane to maleic anhydride. n-Butane gas is now being used in many industrial processes, in fixed bed reactors to convert the gas to maleic anhydride. Catalysts were calcined under high temperatures under a nitrogen atmosphere. It was found that with an increase in reaction temperature, there was an increase in conversion of n-butane to maleic anhydride. Selectivity of the product also showed an increase with an increase in temperature at a Gas Hourly Space Velocity (GHSV) of 1960-2170hr-1. Catalysts were characterized using different techniques such as Electron Dispersive X-Ray Spectroscopy, Inductively Coupled Plasma-Atomic Emission Spectroscopy, Fourier Transform - Infra Red, Average Oxidation State, Brunauer Emmett and Teller (surface area), X-Ray Diffraction and Scanning Electron Microscopy. The 0.6% Ru promoted VPO catalyst showed to be most effective in terms of conversion, selectivity and yield, at a temperature of 450°C as compared to the other catalysts studied. The catalysts degenerated after being subjected to higher temperatures. The selectivity obtained by this catalyst was at 70.2% and the yield obtained was 37%. This study showed that with an increase in Ru up to a certain concentration (0.6%), an increase in selectivity and yield was observed, thereafter, with additional Ru doping, a decrease in selectivity and yield was obtained. / Thesis (M.Sc.)-University of Natal, 2003.

Co promoted and unpromoted vanadium-phosphorous-oxide (VPO) catalysts were synthesized via an organic route. The catalyst precursor was calcined and then conditioned in a reactor, forming the active vanadyl pyrophosphate, (VO)2P2O7, phase. Different promoter loaded catalysts were synthesized and their effect on the yield of maleic anhydride (MA) from n-butane oxidation was examined at different temperatures and gas hourly space velocities (GHSV). The catalysts were tested as a powder. The catalysts were examined in the oxidation of n-butane gas, over air as an oxidant, in a specially designed and constructed continuous flow, fixed-bed catalytic micro-reactor equipped with an on-line gas chromatography (GC) monitoring system. A thermal conductivity detector (TCD) was employed for carbon oxide monitoring and a flame ionization detector (FID) for all other products. The catalysts were characterised by X-ray diffraction (XRD) to determine the phases present in the precursor, calcined and used catalysts. The Brunauer-Emmet-Teller (BET) surface area was calculated for the different promoter loaded catalysts. Fourier transform infrared (FT-IR) spectra, via the KBr pellet method, and attenuated total reflectance (ATR) spectra were recorded to determine the anions present in the bulk and surface of the catalyst respectively. Energy dispersive X-ray (EDX) and inductively couple plasma-atomic emission spectroscopic (ICP-AES) techniques were employed to determine the elemental composition on the surface and in the bulk of the catalyst respectively. Scanning electron microscopic (SEM) images of the catalysts during different stages of their investigation were recorded. The average vanadium oxidation state (AV) in the bulk of the catalyst was determined via a titrimetric method. The catalysts were optimized to a high yield and selectivity of MA. The operating temperature, GHSV and promoter loading on the catalyst were the parameters that were changed during the testing of the catalyst. Different stages of the catalyst's life were characterised via the techniques mentioned above. The catalysts were monitored over a 200-hour period on average, usually taking approximately 24 hours to equilibrate. One such Co promoted catalyst yielded 45 % MA at 275°C and GHSV of 2878 hr-1 on equilibration, with an n-butane conversion of 73 %, whilst all previously reported VPO catalysts produce far lower MA yields at this temperature. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO[4subscript][dot in middle of line]0.5H[2subscript]O (the precursor) followed by in-situ activation to produce (VO)[2subscript]P[2subscript]O[subscript]7 (the active phase). These catalysts considerably improve their performance when prepared as nanostructured materials and this study discusses an alternative synthesis method based on sol-gel techniques capable of producing nanostructured VPO. Vanadium(V) triisopropoxide oxide was reacted with ortho-phosphoric acid in tetrahydrofuran (THF). This procedure yielded a gel of VOPO[4subscript] with interlayer entrapped molecules. The gels were dried at high pressure in an autoclave with controlled excess and composition of THF-2-propanol mixtures. The surface area of the obtained materials was between 50 and 120 m[2superscript]/g. Alcohol produced by the alkoxide hydrolysis and incorporated along with the excess solvent reduced the vanadium during the drying step. Therefore, after the autoclave drying, the solid VOPO[4subscript] was converted to the precursor; and, non-agglomerated platelets were observed. Use of additional 2-propanol increased the amount of precursor in the powder but reduced its surface area and increased its crystallite size. In general, sol-gel prepared catalysts were significantly more selective than the traditionally prepared materials, and it is suggested that the small crystallite size obtained in the precursor influenced the crystallite size of the active phase increasing their selectivity towards maleic anhydride. The evaluation of these materials as catalysts for the partial oxidation of n-butane at 673 K under mixtures of 1.5% n-butane in air yielded selectivity of 40% at 50% conversion compared to 25% selectivity at similar level of conversion produced by the traditionally prepared catalysts. Variations in the catalytic performance are attributed to observed polymorphism in the activated materials, which is evidenced by remarkable differences in the intrinsic activity. All precursors and catalysts were characterized by IR, XRD, SEM and BET, and the products of the catalytic tests were analyzed by GC.