A vanadium phosphorus oxide catalyst synthesized in rotating packed bed for high-efficiency selective oxidation of n-butane

Oxidation of n-butane to produce maleic anhydride (MA) by the vanadium phosphorus oxide (VPO) catalyst is important for the fine chemical industry. However, the improvement in MA yield exceeding 60% is still a big challenge. In this article, a VPO catalyst with increased MA yield originated from the tailored structure of VPO precursor prepared in a rotating packed bed (RPB) reactor with excellent micro-mixing efficiency. The activated VPO-RPB catalyst displayed the coexistence of X₁-VOPO₄ and α_I-VOPO₄ phases and enhanced reducibility of V⁴⁺ state. Remarkably, the MA yield in n-butane oxidation catalyzed by VPO-RPB reached up to 66%, showing an increment by 14% compared with VPO-STR prepared in a stirring tank reactor (STR). The VPO-RPB showed the repeatable catalytic performance and achieved a promising scale-up production. This work provides the experimental evidence of a dual-phase (X₁-VOPO₄ and α_I-VOPO₄) mechanism for n-butane oxidation, and reveals the structure–activity dependence of VPO catalyst.     

Influence of Rare-Earth and Bimetallic Promoters on Various VPO Catalysts for Partial Oxidation of n-Butane

Vanadium phosphorous oxide (VPO) catalyst was prepared using dihydrate method and tested for the potential use in selective oxidation of n-butane to maleic anhydride. The catalysts were doped by La, Ce and combined components Ce + Co and Ce + Bi through impregnation. The effect of promoters on catalyst morphology and the development of acid and redox sites were studied through XRD, BET, SEM, H₂-TPR and TPRn reaction of n-butane/He. Addition of rare-earth element to VPO formulation and drying of catalyst precursor by microwave irradiation increased the fall width at half maximum (FWHM) and reduced the crystallite size of the Vanadyl hydrogen phosphate hemihydrate (VOHPO₄ · 1/2 H₂O, VHP) precursor phase and thus led to the production of final catalysts with larger surface area. The Ce doped VPO catalyst which, assisted by the microwave heating method, exhibited the highest surface area. Moreover, the addition of promoters significantly increased catalyst activity and selectivity as compared to undoped VPO catalyst in the oxidation reaction of n-butane. The H₂-TPR and TPRn reaction profiles showed that the highest amount of active oxygen species, i.e., the V⁴⁺–O^? pair, was removed from the bimetallic (Ce + Bi) promoted catalyst. This pair is responsible for n-butane activation. Furthermore, based on catalytic test results, it was demonstrated that the catalyst promoted with Ce and Bi (VPOD1) was the most active and selective catalyst among the produced catalysts with 52% reaction yield. This suggests that the rare earth metal promoted vanadium phosphate catalyst is a promising method to improve the catalytic properties of VPO for the partial oxidation of n-butane to maleic anhydride.     

Preparation of Novel Composite VPO/Fumed Silica Catalyst for Partial Oxidation of n-Butane

By applying fumed SiO₂ and the deposition–precipitation method based on organic medium, the composite VPO/fumed SiO₂ catalysts were first prepared and tried for partial oxidation of n-butane to maleic anhydride. In the temperature range of 653–693 K the fumed SiO₂-based catalysts not only showed good activity but also maintained sufficiently high MA selectivity in comparison to some conventional supported VPO catalysts. As an example, the catalyst with 30% VPO content showed butane conversion of 60% and MA selectivity of 58 mol% at 673 K. The turnover rates of low loading samples are found to be higher than that of high loading sample as well as unsupported catalyst. Besides the unique interaction which may exist between VPO component and the fumed SiO₂ material, co-existence of dominant (VO)₂P₂O₇ and minor VOPO₄ in these non-equilibrated catalysts may be favorable for MA formation. Moreover, introducing the additive of polyethylene glycol (PEG) in the preparation medium can obviously enhance the dispersion of VPO component and hence lead to a more selective catalyst.     

温和条件下环己烷液相选择性氧化改性VPO催化剂

将La、Ce和Bi改性的钒磷氧化物（VPO）催化剂用于温和条件下液相催化氧化环己烷.发现Bi-VPO催化剂具有较好的液相催化氧化性能;Bi-VPO催化氧化环己烷的优化工艺条件是在10 ml乙腈中加入2 mmol的环己烷、0.01 g (V: 0.068 mmol)的Bi-VPO催化剂,在60 ℃下分次滴加3 ml (26 mmol) H₂O₂,反应12 h,环己烷的转化率为72%,环己酮和环己醇的收率分别为38%和34%.表明改性后的催化剂可大大提高VPO催化剂液相氧化环己烷的催化性能.     

Modeling and optimization of industrial Fischer–Tropsch synthesis with the slurry bubble column reactor and iron-based catalyst

To optimize industrial Fischer–Tropsch(FT) synthesis with the slurry bubble column reactor(SBCR) and ironbased catalyst, a comprehensive process model for FT synthesis that includes a detailed SBCR model, gas liquid separation model, simplified CO_2 removal model and tail gas cycle model was developed. An effective iteration algorithm was proposed to solve this process model, and the model was validated by industrial demonstration experiments data(SBCR with 5.8 m diameter and 30 m height), with a maximum relative error b 10% for predicting the SBCR performances. Subsequently, the proposed model was adopted to optimize the industrial SBCR performances simultaneously considering process and reactor parameters variations. The results show that C_(5+) yield increases as catalyst loading increases within 10–70 ton and syngas H_2/CO value decreases within1.3–1.6, but it doesn't increase obviously when the catalyst loading exceeds 45 ton(about 15 wt% concentration).Higher catalyst loading will result in higher difficulty for wax/catalyst separation and higher catalyst cost. Therefore, the catalyst loading(45 ton) is recommended for the industrial demonstration SBCR operation at syngas H_2/CO = 1.3, and the C_(5+) yield is about 402 ton" per day, which has an about 16% increase than the industrial demonstration run result.     

Effect of Ag, Cu, and Au Incorporation on the Diesel Soot Oxidation Behavior of SiO2: Role of Metallic Ag

The catalytic behaviors of Ag, Cu, and Au loaded fumed SiO₂ have been investigated for diesel soot oxidation. The diesel soot generated by burning pure Mexican diesel in laboratory was oxidized under air flow in presence of catalyst inside a tubular quartz reactor in between 25 and 600 °C. UV–Vis optical spectroscopy was utilized to study the electronic states of Ag, Cu, and Au(M) in M/SiO₂ catalysts. The soot oxidation was seen to be strongly enhanced by the presence of metallic silver on 3 % Ag/SiO₂ surface, probably due to the formation of atomic oxygen species during the soot oxidation process. The catalyst is very stable due to the stability of Ag⁰ species on the catalyst surface and high thermal stability of SiO₂. Obtained results reveal that though the freshly prepared 3 % Cu/SiO₂ is active for soot oxidation, it gets deactivated at high temperatures in oxidizing conditions. On the other hand, 3 % Au/SiO₂ catalyst does not present activity for diesel soot oxidation in the conventional soot oxidation temperature range. The catalytic behaviors of the supported catalyst samples have been explained considering the electron donating ability of the metals to generate atomic oxygen species at their surface.     

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.     

Ultrasonic Pretreatment Transesterification for Solid Basic-Catalyzed Synthesis of Fatty Acid Methyl Esters

Generally, ultrasound irradiation is required throughout the reaction for fatty acid methyl esters (FAME, namely, biodiesel) production, which is energy-consuming and difficult to scale-up. In order to improve the industrial application of ultrasonic technology, a systematic study of ultrasonic pretreatment solid basic (Na₂SiO₃)-catalyzed transesterification for FAME production from cottonseed oil was carried out, and the effect of ultrasonic waves on the properties of Na₂SiO₃ catalyst was assessed by X-ray diffraction (XRD), Fourier transform Infrared (FTIR) and scanning electron microscopy (SEM) characterization of fresh and collected catalysts. An ultrasonic frequency of 30 kHz, ultrasonic power of 200 W and ultrasonic pretreatment irradiation time of 30 min was determined to guarantee a satisfactory degree of transesterification. The optimum production was achieved in the reaction system at 45 °C with methanol/cottonseed oil molar ratio 5:1, catalyst dosage 3% and stirring speed 350 rpm resulting in a FAME yield of above 97% after 60 min of reaction under mechanical stirring with the ultrasonic pretreatment process. The new process has a shorter reaction time, a more moderate reaction temperature, a less amount of methanol and catalyst than only the mechanical stirring process without essential damage to activity and the structure of catalyst. These results are of great significance for applying the ultrasonic pretreatment method to produce FAME.     

Ammoxidation of 3-picoline to nicotinonitrile over vanadium phosphorus oxide-based catalysts

Ammoxidation of 3-picoline to nicotinonitrile was investigated on vanadium phosphorus oxide (VPO), VPO/SiO₂ and additive atom (Cu, Zr, Mn and Co) incorporated VPO catalysts under atmospheric pressure and at 673 K. For the purpose of comparison a conventional V₂O₅–MoO₃/Al₂O₃ catalyst was also studied under identical conditions. These catalysts were characterized by means of X-ray diffraction, electron spin resonance, infrared, ammonia chemisorption and BET surface area methods. The VPO-based catalysts show better performance than the V₂O₅–MoO₃/Al₂O₃ catalyst. Further, the VPO/SiO₂ and VPO catalysts exhibit better conversion and product selectivities than the additive-containing VPO catalysts. Better activity of VPO and VPO/SiO₂ catalysts was related to their high active surface area, higher surface acidity and lower oxidation state of vanadium. The redox couple between (VO)₂P₂O₇ (V⁴⁺) and α_I-VOPO₄ (V⁵⁺) phases appears to be responsible for the ammoxidation activity of VPO catalysts. © 1998 SCI.     

Controlling factors in the selective conversion of n-butane over promoted VPO catalysts at low temperature

Unpromoted and 1.2, 2.3 and 4.3 molar % Co:V cobalt-promoted vanadium-phosphorous-oxide (VPO) catalysts were synthesized via an organic route. The catalyst precursors were calcined and then conditioned in a reactor, forming the active vanadyl pyrophosphate (VO)₂P₂O₇ phase, which was confirmed via X-ray diffraction studies (XRD). The effect of co-promotion on the yield of maleic anhydride (MA) from n-butane oxidation was examined at different temperatures and gas hourly space velocities (GHSV). 2.3% Co:V was the optimum promoter loading for a high yield towards MA. Higher GHSV's proved to enhance the selectivity towards MA.

The catalysts were tested over a 200 h period, generally taking some 24 h to reach steady-state performance. The best performing catalyst yielded 45% MA at 275 °C and a GHSV of 7200 ml g⁻¹ h⁻¹, with an n-butane conversion of 73%, whilst all previously reported VPO catalysts produced far lower MA yields at this temperature.     

Oxidative desulfurization of dibenzothiophene over Fe promoted Co–Mo/Al_2O_3 and Ni–Mo/Al_2O_3 catalysts using hydrogen peroxide and formic acid as oxidants

This work reports the enhancing effect of a highly cost effective and efficient metal, Fe, incorporation to Co or Ni based Mo/Al_2O_3 catalysts in the oxidative desulfurization(ODS) of dibenzothiophene(DBT) using H_2O_2 and formic acid as oxidants. The influence of operating parameters i.e. reaction time, catalyst dose, reaction temperature and oxidant amount on oxidation process was investigated. Results revealed that 99% DBT conversion was achieved at 60 °C and 150 min reaction time over Fe–Ni–Mo/Al_2O_3. Fe tremendously enhanced the ODS activity of Co or Ni based Mo/Al_2O_3 catalysts following the activity order: Fe–Ni–Mo/Al_2O_3 NFe–Co–Mo/Al_2O_3 NNi–Mo/Al_2O_3 NCo–Mo/Al_2O_3, while H_2O_2 exhibited higher oxidation activity than formic acid over all catalyst systems. Insight about the surface morphology and textural properties of fresh and spent catalysts were achieved using scanning electron microscopy(SEM), X-ray diffraction(XRD), energy dispersive X-ray(EDX)analysis, Atomic Absorption Spectroscopy(AAS) and BET surface area analysis, which helped in the interpretation of experimental data. The present study can be deemed as an effective approach on industrial level for ODS of fuel oils crediting to its high efficiency, low process/catalyst cost, safety and mild operating condition.     

Regeneration studies of redox catalysts

Cited advantages of circulating fluidized bed reactors (CFB) include higher selectivity and conversion together with the ability to optimize the process conditions of each vessel independently—temperature, gas partial pressure and residence time. DuPont commercialized a CFB process to produce maleic anhydride in which a vanadium pyrophosphate (VPO) was cycled between a fast bed riser and an air fed regenerator. Together with VPO, we examined two other redox catalyst systems—MoVSb (acrylic acid from propane) and FeMoO (methanol to formaldehyde).The lattice oxygen capacity of the FeMoO catalyst was about five times higher than either the VPO or MoVSb with little adsorbed carbon but a significant quantity of chemisorbed water. Above 350 °C, carbon deposition was detected and increased with increasing temperature. Carbon deposition decreased with increasing temperature for the MoVSb system and its lattice oxygen capacity was slightly higher than for VPO. The carbon deposition pattern for VPO was the opposite of the MoVSb and increased with temperature. Based on a hydrogen and carbon mass balance during the catalyst re-oxidation treatment, the molecular composition of the adsorbed species were C₄H₆ and C₃H₃—like for the VPO and MoVSb, respectively.Based on the high lattice oxygen capacity, the formaldehyde reaction appears to be ideally suited for development in a CFB. Whereas the lattice oxygen contribution of the MoVSb is equivalent to VPO, less oxygen is required to produce acrylic acid (compared to maleic anhydride) so the incentive of developing a CFB process should be greater than for butane oxidation to maleic anhydride.     

A Study on VPO Specimen Supported on Aluminum-Containing MCM-41 for Partial Oxidation of n-Butane to MA

Dispersed vanadium–phosphorus oxide species supported on Al-MCM-41 with different vanadium loadings have been synthesized for the first time for partial oxidation of butane to MA. It was found that the VPO species was dispersed over the Al-MCM-41 support material, both in the internal channel and on the external surface. With increasing vanadium loading, n-butane conversion increased but MA selectivity decreased considerably under the same reaction conditions. At lower conversions (<30%), rather high MA selectivity (ca. 70%) can be achieved on the low loading sample. Compared with the amorphous structure of large pore SiO₂ support, the unique structure of the MCM-41 and the incorporated Al³⁺ in the framework do have an impact on the reaction behavior of the supported VPO specimen. The chemical nature of the supported VPO species and the interaction between the applied VPO species and the support was found to vary notably with the content of vanadium in the sample and likewise affected the related physico-chemical characteristics and their reaction behaviors.     

Adhesion optimization for catalyst coating on silicon-based reformer

CMZ (ca. 30.0 wt.% Cu, 20 wt.% Mn, and 50 wt.% Zn) catalyst was chosen for the partial oxidation of methanol (POM) reaction. To enhance adhesion between a silicon-based reactor and catalysts, boehmite and bentonite were used as binders. Changes in conditions such as pH value, ratio of bentonite/boehmite, amount of solid contents per area of substrate, and aging time have crucial effects on adhesion and result in variable performance of catalyst in POM reaction. Regarding optimized adhesion conditions, 13 wt.% weight loss was observed and methanol conversion could be kept at ca. 80–90% of original catalyst performance in a packed-bed reactor. However, poor performance was observed in the micro-channel reactor. The methanol conversion (C_MeOH), H₂ selectivity (S_H2), and H₂ yield (Y_H2) achieved 58%, 67%, 5.7 × 10^?6 mol/min in micro-channel reformer at 250 °C, respectively.     

Compact Reforming Process Using High-Performance and Long-Lived CO Preferential Oxidation over an Activated Ru/Al2O3 Catalyst for PEFC

Compact natural gas reforming process using high-performance and long-lived CO preferential oxidation (PROX) over an activated Ru/Al₂O₃ catalyst has been developed for residential polymer electrolyte fuel cell (PEFC) systems. The long-term durability of the catalyst was demonstrated for more than 40,000 h. After 40,000 h operation, CO was removed from a reformed gas to below 1 ppm on the activated Ru/Al₂O₃ catalyst at [O₂]/[CO] = 1.5. The high activity and selectivity of the catalyst were maintained for more than 40,000 h. Moreover, the start–stop durability for more than 3,000 cycles of the activated Ru/Al₂O₃ catalyst was also demonstrated without N₂ purge.     

Bismuth-Modified Vanadyl Pyrophosphate Catalysts

A 1 bismuth-doped VPO catalyst was prepared by refluxing Bi(NO₃)₃ and VOPO₄ 2H₂O in isobutanol. The incorporation of Bi into the VPO lattice lowered the overall V oxidation state from 4.24 to 4.08. It also lowered both the peak maximum temperature for the desorption of oxygen from the lattice from 1001K (undoped) to 964K with a shoulder at 912K and the peak maxima for H₂ temperature-programed reduction from 863, 1011 and 1143K (undoped) to 798, 906 and 1151K. The total oxygen desorbed from the Bi-doped catalyst was only one-fourth that of the undoped catalyst, while the amount of oxygen removed by TPR was roughly the same for both catalysts. These results suggest that in anaerobic oxidation, the Bi-doped catalyst will have roughly the same activity as in undoped catalyst in C₄ hydrocarbon oxidation but will have a higher selectivity to products such as olefins and maleic anhydride.     

Progress of vanadium phosphorous oxide catalyst for n-butane selective oxidation

The utilization of lighter alkanes into useful chemical products is essential for modern chemistry and reducing the CO₂ emission. Particularly, n-butane has gained special attention across the globe due to the abundant production of maleic anhydride (MA). Vanadium phosphorous oxide (VPO) is the most effective catalyst for selective oxidation of n-butane to MA so far. Interestingly, the VPO complex exists in more or less fifteen different structures, each one having distinct phase composition and exclusive surface morphology and physiochemical properties such as valence state, lattice oxygen, acidity etc., which relies on precursor preparation method and the activation conditions of catalysts. The catalytic performance of VPO catalyst is improved by adding different promoters or co-catalyst such as various metals dopants, or either introducing template or structural-directing agents. Meanwhile, new preparation strategies such as electrospinning, ball milling, hydrothermal, barothermal, ultrasound, microwave irradiation, calcination, sol–gel method and solvothermal synthesis are also employed for introducing improvement in catalytic performance. Research in above-mentioned different aspects will be ascribed in current review in addition to summarizing overall catalysis activity and final yield. To analyze the performance of the catalytic precursor, the reaction mechanism and reaction kinetics both are discussed in this review to help clarify the key issues such as strong exothermic reaction, phosphorus supplement, water supplement, deactivation, and air/n-butane pretreatment etc. related to the various industrial applications of VPO.     

An Extremely Active Pt/Carbon Nano-Tube Catalyst for Selective Oxidation of CO in H2 at Room Temperature

Pt catalyst supported on carbon nano-tube (CNT) was extremely active for the selective oxidation of CO in H₂ at room temperature, which was remarked contrast to the Pt supported on an active carbon (Vulcan carbon) and a graphite powder. Complete oxidation of CO was attained on a 5 wt.% Pt/CNT catalyst (0.8 g) at ca. 40 °C when the O₂/CO ratio in a flow of H₂ (20 mL/min) + CO (3.0 mL/min) + O₂ + N₂ was adjusted to be larger than 0.75 at the total flow rate of 100 mL/min. Specific activity of the Pt/CNT catalyst was explained by efficient provision of reactant molecules diffusing on CNT surface to Pt particles.     

Catalytic Removal of Toluene over Co3O4–CeO2 Mixed Oxide Catalysts: Comparison with Pt/Al2O3

The catalytic oxidation of toluene, chosen as VOC probe molecule, was investigated over Co₃O₄, CeO₂ and over Co₃O₄–CeO₂ mixed oxides and compared with the catalytic behavior of a conventional Pt(1 wt%)/Al₂O₃ catalyst. Complete toluene oxidation to carbon dioxide and water was achieved over all the investigated systems at temperatures below 500 °C. The most efficient catalyst, Co₃O₄(30 wt%)–CeO₂(70 wt%), showed full toluene conversion at 275 °C, comparing favorably with Pt/Al₂O₃ (100% toluene conversion at 225 °C).     

A Thermodynamic Investigation of the Redox Properties of VPO Catalysts

Abstract  

The redox properties of a vanadium phosphorus oxide (VPO) catalyst with a V:P ratio of one were investigated using Coulometric Titration at 873 K. Equilibrium between (VO)₂P₂O₇ and VOPO₄ exists at a P(O₂) of 3 × 10⁻⁴ atm, corresponding to ΔG of −60 kJ/mol O₂. This value for VPO is significantly lower than that measured with other vanadium-containing catalysts that have been studied. Furthermore, compared to other vanadium catalysts, V⁺⁴ was stabilized against further reduction at lower P(O₂). These redox thermodynamics may help to explain the unique catalytic properties of VPO catalysts for partial oxidation of butane to maleic anhydride.