Preparation of pyridinemonocarboxylic acids by catalytic vapour phase oxidation of alkylpyridines. II. Oxidation of 2-methyl-5-ethylpyridine to niacin

The vapour phase air oxidation of 2-methyl-5-ethylpyridine (MEP) has been investigated, and the various oxidation products identified. Using a doubly promoted vanadium catalyst, V₂O₅–TiO₂–K₂O, a 98% (mole) conversion of MEP was obtained with a yield of 36% for niacin and 18% for recirculatable products (i.e. products with an intact 3-picoline skeleton) at a temperature of 413°C and a space velocity of 5500 h^?1. In a comparison of the singly promoted catalysts, varying the atom ratio V/Ti, the catalyst with V/Ti = 100/25 was found to be most active. In a comparison of different preparation temperatures for the same catalyst, 1250°C was found to be most satisfactory. A reaction scheme is proposed with the corresponding rate constants and apparent activation energies.     

Kinetics and mechanism of the vapour phase oxidation of 3-picoline by nitric oxide over nickel oxide–aluminium oxide catalyst

The kinetics of the catalytic transformation of 3-picoline to 3-cyanopyridine by nitric oxide (NO) have been investigated over nickel oxide-aluminium oxide catalyst (2NiO·Al₂O₃) in a differential flow reactor between 300 and 360°C. A maximum yield of 98% was achieved with a catalyst having a Ni: Al atomic ratio of 1:1 and preheated in the presence of air at 600°C for 24 h. The rate equation R_n = k_pk_nP_pP_n/(k_pP_p + k_nP_n) deduced, assuming a steady state involving a two-stage irreversible oxidation-reduction process, represented the data most satisfactorily for conversion of 3-picoline to nicotinonitrile. A tentative mechanism for the reaction is proposed.     

Kinetics of the vapour phase oxidation of ethyl alcohol on vanadium pentoxide catalyst

The kinetics of V₂O₅-catalysed vapour phase oxidation of ethyl alcohol were studied with the help of a differential fixed-bed flow reactor. The partial pressures of alcohol, oxygen and water were varied in the ranges: 6–10 × 10^–3 atm, 1–10 % × 10^–1 atm, and 0–169 × 10^–3 atm respectively in the temperature range 228–264 °C. The rate equation: deduced by the assumptions of the steady-state redox mechanism, was found to conform to the experimental results. The energies of activation for the partial reactions, namely reduction and oxidation of the catalyst, were found to be 18.9 and 11.8 kcal/mol. The influence of different products was also studied in detail.     

Vanadia-molybdena catalysts for the oxidation of 2-picoline

A study has been made of the influence of catalyst composition on the gas phase oxidation of 2-picoline over mixed vanadium and molybdenum oxides supported on kieselguhr. It is shown that the formation of partial oxidation products is associated with the existence of a mixed oxide phase. The selectivity for the formation of pyridine-2-aldehyde reaches a maximum when one in six vanadium(V) ions in the V₂O₅ lattice is replaced by a molybdenum(VI) ion. It is suggested that the origin of the selectivity is the formation of isolated (V⁴⁺-O) species.     

Experimental investigation and mathematical modelling of water vapour corrosion of Ti3SiC2 and Ti2AlC ceramics and their mechanical behaviour

Commercially available Ti₃SiC₂ and Ti₂AlC ceramics were used in this study to investigate their wet corrosion and mechanical behaviour as they were under investigation for years for their applications in the field of nuclear as cladding materials and aerospace. The test coupons of dimension 3 × 4 × 40 mm³ and 3 × 4 × 20 mm³ were machined out from commercially available samples for the 3-pt bend test and wet corrosion test, respectively. The water vapour corrosion studies of these samples were carried out at 800 ℃, 1000 ℃, 1200 ℃ for 10, 20 and 100 h in gas flow condition containing 50 % steam + 50 % air. Phase analysis of the as-received Ti₃SiC₂ and Ti₂AlC ceramics revealed the presence of other impurity phases such as TiC and TiSi₂. The XRD patterns of the oxidised samples show the formation of rutile as the major phase in both materials. The oxidation layer formed on Ti₃SiC₂ sample was measured to be 280 μm after exposing the sample in steam for 100 h at 1200 °C. The water vapour corrosion studies reveal that Ti₂AlC has high oxidation resistance compared with the Ti₃SiC₂ due to the formation of protective layers of TiO₂ and Al₂O₃ which resulted in reduced weight gain and oxidation layer thickness. Three-point bend tests were conducted at room temperature for the samples after the water vapour corrosion test at 1000 °C/100 h. The TAC samples showed no degradation in the bending strength (244 MPa) whereas the TSC samples showed reduced strength of 320 MPa. The tensile strength of the samples was measured at room temperature and hydrothermal condition (250 °C and 250 bars pressure) and it was observed that Ti₃SiC₂ had high tensile strength (190 MPa) in hydrothermal conditions. The tensile strength results were validated using Finite element analysis (FEA) using ANSYS and the FEA results showed a negligible variance of 7 % compared with experimental method. Mathematical modelling based on one dimensional solution of diffusion equation combined with Deal-Grove model was employed to study and compare the oxidation thickness for the linear and parabolic models for the ceramics. The model was effective in validating the oxidation thickness of Ti₃SiC₂ showing that the experimental thickness was closer to that of mathematical model.     

Vanadium oxide catalysts on structured microfiber supports for the selective oxidation of hydrogen sulfide

Vanadium(V) oxide catalysts for the selective oxidation of hydrogen sulfide to sulfur on a nonporous glass-fiber support with a surface layer of a porous secondary support (SiO₂) are studied. The catalysts are obtained by means of pulsed surface thermosynthesis. Such catalysts are shown to have high activity and acceptable selectivity in the industrially important region of temperatures below 200°C. A glass-fiber catalyst containing vanadium oxide (10.3 wt % of vanadium) in particular ensures the complete conversion of H₂S at a temperature of 175°C and a reaction mixture hourly space velocity (RMHSV) of 1 cm³/(g_cat s) with a sulfur yield of 67%; this is at least 1.35 times higher than for the traditional iron oxide catalyst. Using a structured glass-fiber woven support effectively minimizes diffusion resistance and greatly simplifies the scaleup of processes based on such catalysts. Such catalysts can be used for the cleansing of tail gases from Claus units and in other processes based on the selective oxidation of H₂S.     

An in-situ Reduction/Oxidation XAS Study on the EL10V8 VO x /TiO2(Anatase) Powder Catalyst

The structural changes of the supported vanadium oxide in the V₂O₅/TiO₂(anatase) EUROCAT EL10V8 powder catalyst during reduction and oxidation at 420 and 490 °C were studied with in-situ X-ray absorption spectroscopy (XAS). The Vanadium K-edge XAS results are compared with pure bulk V₂O₅. For the reduction–oxidation cycle at 420 °C, similar structural changes as for bulk V₂O₅ were observed for the supported vanadium oxide: a reduction to the VO₂ structure and re-oxidation back to V₂O₅. After reduction at 490 °C however, a different structure was obtained: very regular “VO₆” octahedra with a V^2.8+ valence. This may point to a structural support effect.     

Studies on the conditions of synthesis of picolinic acid by heterogeneous catalytic oxidation of 2-picoline

Heterogeneous oxidation of 2-picoline over binary P–Ti, Sb–Ti, P–Sb, and V–Ti oxide catalysts was studied over the temperature range of 200–300°C. The vanadium–titanium catalysts based on titanium dioxide (anatase) were found to be the most selective for picolinic acid. With binary catalysts containing 20–50% of vanadium pentoxide, the selectivity for picolinic acid was 19–22% at the 36–74% conversion of 2-picoline. A distinguishing feature of these catalysts is regular surface stacking of V₂O₅ and TiO₂ crystallites.     

Catalytic role of vanadium(V) sulfate on activated carbon for SO2 oxidation and NH3-SCR of NO at low temperatures

Carbon-supported catalyst with vanadium(V) sulfate (V₂O₃(SO₄)₂) as active component was prepared, characterized and tested for SO₂ and NO catalytic removal. Result shows that this catalyst is very active towards SO₂ oxidation and selective catalytic reduction of NO with NH₃ in the low temperature range of 100–250 °C.     

Reactive synthesis for porous TiVAlC ceramics by TiH2,V,Al and graphite powders

Using the mixed powder of TiH₂, graphite, aluminum and vanadium as starting materials, porous TiVAlC ceramics were fabricated by the reactive synthesis technology at 1300 °C. The chemical steadiness of porous TiVAlC along with the effects of sintering temperature on the viscous permeability coefficient, strength, porosity, pore size and volume expansion rate of the porous TiVAlC were explored, and the mechanism of pore formation was also revealed. The preparation process includes five steps as follows: (i) the complete decomposition of stearic acid at 500 °C; (ii) the pyrolysis of TiH₂ at 700 °C, converting TiH₂ into hydrogen and titanium (iii) The solid-liquid chemical reaction of solid vanadium, titanium and molten aluminum at 700 °C, converting the mixture into V–Al and Ti–Al compounds; (iv) At 900–1100 °C, Surplus V and Ti interact with graphite to synthesize carbides of TiVC₂, VC, and TiC; (v) Reactive synthesized carbides (TiVC₂, VC, and TiC), Ti₂AlC, V–Al and Ti–Al compounds that yield porous TiVAlC at 1300 °C.     

Single step direct coating of 3-way catalysts on cordierite monolith by solution combustion method: High catalytic activity of Ce 0.98Pd0.02O2-δ

A new process of coating of active exhaust catalyst over γ-Al₂O₃ coated cordierite honeycomb is reported here. The process consists of (a) growing γ-Al₂O₃ on cordierite by solution combustion of Al(NO₃)3 and oxylyldihydrazide (ODH) at 600 °C and active catalyst phase Ce_0.98Pd_0.02O_2-δ on γ-Al₂O₃ coated cordierite again by combustion of ceric ammonium nitrate and ODH with 1.2 × 10⁻³ M PdCl₂ solution at 500 °C. Weight of active catalyst can be varied from 0.02 to 2 wt% which is sufficient but can be loaded even up to 12 wt% by repeating dip dry combustion. Adhesion of catalyst to cordierite surface is via oxide growth which is very strong. About 100% conversion of CO is achieved below 80 °C at a space velocity of 880 h⁻¹. At much higher space velocity of 21,000 h⁻¹, 100% conversion is obtained below 245 °C. Activation energy for CO oxidation is 8.4 kcal/mol. At a space velocity of 880 h⁻¹ 100% NO conversion is attained below 185 °C and 100% conversion of ‘HC’ C₂H₂ below 220 °C. At same space velocity 3-way catalytic performance over Ce_0.98Pd_0.02O_2-δ coated monolith shows 100% conversion of all the pollutants below 220 °C with 15% of excess oxygen. In this method, handling of nano material – powder is avoided.     

Room temperature synthesized spherical V-MCM-41: a catalyst for vapour phase oxidation of diphenylmethane

Mesoporous spherical Si-MCM-41 and V-MCM-41 materials with a variable Si/V ratio of 25, 50, 75 and 100 were prepared by an economical route at room temperature and characterized by various techniques for qualitative and quantitative understanding of vanadium species. The morphology and mesoporosity of the spherical particles were confirmed by SEM and TEM micrographs. The catalytic activity of the synthesized catalysts was tested for vapour phase oxidation of diphenylmethane to benzophenone using CO₂ free air as oxidant at atmospheric pressure. The conversion of diphenylmethane and selectivity for benzophenone were measured in the temperature range of 593?C713?K over V-MCM-41 catalysts synthesized by adopting room temperature method as well as by direct hydrothermal method. The catalytic performance was related to vanadium content on the surface of the catalysts.     

Kinetics of vapour phase oxidation of furfural on vanadium catalyst

Vapour phase oxidation of furfural over vanadium pentoxide catalyst was studied using an isothermal flow reactor in the temperature range of 220–280°C. Maleic anhydride and carbon dioxide are found to be formed from furfural by a parallel reaction scheme. The following rate equation based on the two-stage redox mechanism—the substance to be oxidized reduces the catalyst which in turn is reoxidized by oxygen from the feed—is found to explain the data satisfactorily.

The reoxidation of the reduced catalyst was found to be the rate controlling step.     

Behaviors of V-doped Titanium Mixed Oxides in the Catalytic Dehydrogenation of Ethylbenzene

By an acid-catalyzed sol–gel method the V-doped titanium oxides (VxDTOs, x _mol% of V/(V + Ti) molar ratio) were prepared and systematically characterized by the techniques of XRD, TEM, H₂-TPR, XPS and TGA, indicating that most of the vanadium in the catalyst was highly dispersed on the surface of and in the bulk phase of TiO₂. The effect of V⁵⁺ doping level (1–9 mol% V⁵⁺) on the surface of TiO₂ and VxDTOs catalytic performance was analyzed. From the catalytic activity evaluation of VxDTOs in the dehydrogenation of ethylbenzene to styrene in the presence of CO₂ (CO₂-EBDH) at 450 °C, V6DTOs catalyst had the highest activity. Its higher activity in CO₂ than in N₂ clearly shows that CO₂ markedly enhanced the dehydrogenation of ethylbenzene. The activity of V6DTOs catalyst could almost be resumed after regeneration by air while partly resumed after regeneration by CO₂.     

Liquid phase oxidation of 2-methyl pyridine to 2-pyridinecarboxylic acid over cobalt-doped SBA-3

Cobalt-doped SBA-3 was synthesized by cogellation method and was used as a catalyst for the oxidation of 2-methyl pyridine in acetic acid using aqueous hydrogen peroxide as oxidant. The catalyst exhibited very high substrate conversion (98%) and good product (2-pyridinecarboxylic acid) selectivity (93%). Fast hot catalyst filtration experiment proved that the catalyst acted as a heterogeneous one and it can be reused two times without losing its activity to a greater extent. The catalyst was characterized by X-ray diffraction, N₂ physisorption, diffuse reflectance UV–vis, and FT-IR.     

ACCELERATION OF THE WET OXIDATION REACTION OF PIPERAZINE BY HETEROGENEOUS Ru/TiO2 CATALYST

Wet air oxidation is a candidate technique for the effective treatment of wastewater contaminated by nitrogenous organic pollutants. Piperazine (PZ) is a cyclic diamine representing this class of compounds. In the present work, the wet oxidation reaction of PZ was studied for the first time. It was found that, in the studied range of temperatures of 180°–230°C and O₂ partial pressures of 0.69–2.07 MPa, the oxidation process was slow. Total organic carbon (TOC) conversion at 230°C and 0.69 MPa O₂ partial pressure was just 52% after 2 h. The investigated reaction was accelerated by a heterogeneous Ru/TiO₂ catalyst. Maximum TOC conversion (91%) was achieved during catalytic wet oxidation at 210°C and 1.38 MPa O₂ pressure. Kinetic data were collected over the range of temperatures 180°–210°C, O₂ partial pressures 0.34–1.38 MPa, and catalyst loading 0.11–0.66 kg/m³. The lumped TOC concentration decay was a two-step first-order process.     

Effects of mercury oxidation on V2O5–WO3/TiO2 catalyst properties in NH3-SCR process

The effects of mercury oxidation on V₂O₅–WO₃/TiO₂ SCR catalyst's physical and chemical properties have been investigated. Both fresh catalyst and mercury exposed catalyst have been examined by BET, XRD, XPS and catalytic activity measurements. Mercury oxidation promoted the V^5 + species transforming to the V^4 + species and consumed the lattice oxygen on the surface of catalyst. In addition, the NO conversion of mercury exposed catalyst decreased in the range of 200 °C to 300 °C. It suggested a competitive relationship between gaseous NH₃ and adsorbed mercury on the catalyst surface in that temperature range.     

Testing of a Ni‐Al2O3 Catalyst for Methane Steam Reforming Using Different Reaction Systems

Ni‐Al₂O₃ catalyst activity was tested for methane steam reforming using two different reaction systems: a catalyst particle bed (0.42–0.5 mm catalyst particles diluted in SiC) with a surface area‐to‐volume ratio SA/V of 910 m^–1 and a porosity ? of 52 % and a catalyst‐coated metal monolith with an SA/V of 3300 m^–1 and an ? of 86 %. Under a steam‐to‐carbon ratio of 2.5 and at a temperature of 700 °C, the highest specific reaction rates were found for the catalyst‐coated monolith. The high SA/V and ?, together with the high rate of heat transfer of the metal monolith were found to be responsible of this optimum behavior. However, in both systems, the Ni‐Al₂O₃ catalyst suffered a catalyst deactivation during operation.     

The beneficial effect of water vapour on the oxidation at 600 and 700 °C of a MoSi2-based composite

The oxidation characteristics of a MoSi₂-based composite in O₂ and O₂+10% H₂O at 600 and 700 °C were investigated. The effects of temperature and water vapour on oxidation were examined. The oxidation kinetics were studied using a thermobalance and furnace exposure, while the morphologies and compositions of the oxides were examined using XRD, ESEM/EDX, and SEM/EDX. We propose that oxidation proceeds by the initial formation of MoO₃ crystals and amorphous SiO₂ on the surface. The MoO₃ is then evaporated; as volatile (MoO₃)₃ species in O₂ and additional MoO₂(OH)₂ species in O₂+10% H₂O, which results in a porous, Mo-depleted oxide. However, the pores in the Mo-depleted SiO₂ scale heal, and a protective crystalline scale is established eventually. The vapour pressures of the abovementioned volatile species increase with temperature and/or water vapour content in the atmosphere, which leads to accelerated Mo depletion from the oxide scale. A shorter time elapses before the oxide scale is transformed into the relatively Mo-free protective SiO₂ scale, which results in less oxide being formed. Thus, the formed scale becomes thinner in O₂+10% H₂O than in O₂. Thereby the Mo removal is beneficial when water vapour is added to the exposure atmosphere.     

Oxidation mechanisms under water vapour conditions of ZrB2-SiC and HfB2-SiC based materials up to 2400 °C

This study aims at observing and understanding the oxidation mechanisms of ZrB₂-20 vol%SiC (ZS), HfB₂-20 vol%SiC (HS) and HfB₂-20 vol%SiC- 3 vol%Y₂O₃ (HSY) materials up to 2400 °C under water vapour conditions. After SPS sintering, fully densified samples were oxidized at several temperatures with 30 vol% H₂O/70 vol% Ar during 20 s. Weight variations as well as post-test microstructural and XRD analyses allowed understanding the influence of the composition on the oxidation behavior and the evolution of each oxide sublayer. Below 1550 °C, oxidation is limited, and thin oxide layers are observed. At 1900 and 2200 °C, ZS and HS show mechanical damage (cracks, spallation), while HSY keeps its structural integrity and interlayer adherence. The addition of Y₂O₃ reduces the damages due to thermal stresses in the material due to the stabilization of the cubic phase of HfO₂, and the formation of a Y₂Si₂O₇ interphase that mitigates thermal expansion mismatch between the SiC-depleted layer and the HfO₂ layer.