低水比乙苯脱氢制苯乙烯催化剂的开发

在铁系催化剂基础上通过引入活性助剂、选择性助剂、抗积炭助剂及创造条件促使铁钾形成K₂Fe₂₂O₃₄晶相，开发出了能适应低水比条件下使用的催化剂。1 000 h稳定性试验和催速老化试验结果表明，催化剂具有良好的活性稳定性，强度高，可以应用于工业装置。     

低钾型乙苯脱氢催化剂的研制

通过引入活性调节剂，双重性能调节剂，结构稳定剂等助催化剂，利用4段连续升温活化技术，制备出了氧化钾质量分数为10％的乙苯脱氢催化剂。结果表明，在反应温度610－620℃，空速0.8-1.0h^-1，水油质量比1.6-2.0的条件下，乙苯转化率，苯乙烯收率，苯乙烯选择性分别为80％，75％，95％，催化剂钾流失现象得到缓解，抗湿性能良好。     

高收率乙苯脱氢催化剂GS-12的工艺条件研究

介绍了高收率乙苯脱氢催化剂GS-12的特性,研究了乙苯脱氢反应温度、水蒸汽与乙苯物质的量比、空速与转化率和选择性的关系,确定了乙苯脱氢催化剂GS-12在实际生产中适宜的工艺条件。工业应用表明,GS-12催化剂活性较高,能够适应较低水蒸汽与乙苯物质的量比,机械强度高,抗粉化性能好,床层阻力降小,使用寿命预期在30个月以上,综合性能达到国际先进水平。     

Kinetics of the dehydrogenation of ethylbenzene to styrene over unpromoted and K-promoted model iron oxide catalysts

The dehydrogenation of ethylbenzene to styrene over unpromoted and potassium-promoted model iron oxide catalysts has been studied using ultrahigh vacuum techniques in conjunction with elevated pressure reaction kinetics. Model iron oxide catalysts were prepared by oxidizing a polycrystalline Fe sample that was subsequently dosed with metallic potassium. At 875 K the unpromoted catalyst exhibited a turnover frequency of 5×10^–4 molecules/ site s and an activation energy of 39 kcal/mol, both in excellent agreement with the results found for an analogous iron oxide powder catalyst. Potassium promotion increased the turnover frequency to 1.0×10^–3 molecules/site s and lowered the activation energy to 36 kcal/mol for the dehydrogenation reaction. Similarities between the activation energies on the unpromoted and promoted catalysts indicate that the active site is the same on both catalysts. Creation of the active site was dependent upon the formation of an Fe³⁺ metastable species, consistent with the formation of a KFeO₂ phase, upon the addition of potassium.     

Dehydrogenation of ethylbenzene to styrene over Fe2O3/Al2O3 catalysts in the presence of carbon dioxide

An Fe₂O₃ (10 wt%)/Al₂O₃ (90 wt%) catalyst prepared by a coprecipitation method was found to be effective for dehydrogenation of ethylbenzene to produce styrene in the presence of CO₂ instead of steam used in commercial processes. The dehydrogenation of ethylbenzene over the catalyst in the presence of CO₂ was considered to proceed both via a one-step pathway and via a two-step pathway. CO₂ was found to suppress the deactivation of the catalyst during the dehydrogenation of ethylbenzene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reaction mechanism and kinetics for hydrolytic dehydrogenation of ammonia borane on a Pt/CNT catalyst

A reaction mechanism is proposed for hydrolytic dehydrogenation of ammonia borane on a Pt/CNT catalyst. A combination of thermodynamic analysis and FTIR measurement reveals that B‐containing byproducts are mainly in the form of an NH₄B(OH)₄‐B(OH)₃ mixture rather than NH₄BO₂ reported previously. The revised main reaction is , involving the B–H, B–N, and O–H bond cleavages. Isotopic experiments using D₂O instead of H₂O as reactant or introducing D₂ into the reaction atmosphere suggest the O–H bond cleavage being in the rate‐determining step, and an unfavorable occurrence of the chemisorbed H₂O dissociation (i.e., the direct O–H bond cleavage), respectively. Different reaction pathways with indirect O–H bond cleavages are analyzed, and then is suggested as the rate‐determining step. Subsequently, a Langmuir–Hinshelwood kinetic model is developed, which fits well with the experimental data. © 2016 American Institute of Chemical Engineers AIChE J, 63: 60–65, 2017     

Morphology and deactivation behaviour of Co–Ru/γ‐Al2O3 Fischer–Tropsch synthesis catalyst

Deactivation of Co–Ru/γ‐Al₂O₃ Fischer–Tropsch (FT) synthesis catalyst along the catalytic bed over 850 h of time‐on‐stream (TOS) was investigated. Catalytic bed was divided into four parts and structural changes of the spent catalysts collected from each catalytic bed after FT synthesis were studied using BET, ICP, XRD, TPR, carbon determination, H₂ chemisorption and oxygen titration techniques. Rapid deactivation was observed during first 200 h of FT synthesis. In this case, the deactivation rate was not dependent on the number of the catalyst active sites. It was zero order to CO conversion and independent of the size of active sites. Beyond the TOS of 200 h, the deactivation could be simulated with a power law expression: . The physical properties of the catalyst charged in 1st half of the reactor did not change significantly. Interaction of cobalt with alumina and formation of mixed oxides of the form xCoO·yAl₂O₃ and CoAl₂O₄ was increased along the catalytic bed. Percentage reducibility and dispersion decreased by 2.4–25.5% and 0.5–8.8% for the catalyst in the beds 1 and 4, respectively. Particle diameter increased by 0.8–6.1% for the catalyst in the beds 1 and 4 respectively suggesting higher rate of sintering at last catalytic bed. The amount of coke formation in the 4th catalytic bed was 6 times more than that of in bed 1.     

CeO2‐CrOy/γ‐Al2O3 redox catalyst for the oxidative dehydrogenation of propane to propylene

CeO₂‐CrO_y loaded on γ‐Al₂O₃ was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N₂ adsorption‐desorption measurements, H₂‐temperature‐programmed reduction, O₂‐temperature‐programmed desorption, NH₃‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H₂‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO₂ can enhance the oxygen capacity of CrO_y. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO₂ can inhibit the evolution of lattice oxygen (O^2?) to electrophilic oxygen species (O₂^?), causing the average CO_x (CO and CO₂) selectivity to decrease from 9.64% to 6.31%.     

Oxidative dehydrogenation of 4-vinylcyclohexene into styrene over ZrO2 catalyst promoted with Fe2O3 and CaO

The oxidative dehydrogenation of 4-vinylcyclohexene (VCH) into styrene was carried out in the presence of oxygen over a ZrO₂ catalyst promoted with Fe₂O₃ and CaO. Intrinsically, ZrO₂ showed high dehydrogenation activity, which resulted in 80% styrene selectivity with 45% conversion at 425 °C and LHSV 3 h⁻¹. When the ZrO₂ was further promoted with calcium and iron, CaO/Fe₂O₃/ZrO₂, the highest styrene selectivity of 88.9% was obtained as well as the lowest deactivation. The deactivation of catalyst was prohibited properly through the introduction of oxygen in the reactant together with the modification of Fe₂O₃/ZrO₂ with CaO. The CaO/Fe₂O₃/ZrO₂ showed constant catalytic activity and selectivity for more than 50 h without deactivation. The selectivity of styrene was strongly influenced by the mole ratio of O₂/VCH and 95% selectivity with 80% conversion was obtained at O₂/VCH mole ratio of 6 over Fe₂O₃/ZrO₂. It is thought that the oxidative dehydrogenation proceeds through the dehydrogenation (DH) of ring-hydrocarbon of VCH followed by selective combustion of hydrogen (SHC) and the high selectivity of styrene was achieved by the bi-functional role of ZrO₂ for DH and SHC reactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Utilization of carbon dioxide as soft oxidant for oxydehydrogenation of ethylbenzene to styrene over V2O5–CeO2/TiO2–ZrO2 catalyst

Vanadium oxide and cerium oxide doped titania–zirconia mixed oxides were explored for oxidative dehydrogenation of ethylbenzene to styrene utilizing carbon dioxide as a soft oxidant. The investigated TiO₂–ZrO₂ mixed oxide support with high specific surface area (207 m² g⁻¹) was synthesized by a coprecipitation method. Over the calcined support (550 °C), a monolayer equivalent (15 wt.%) of V₂O₅, CeO₂ or a combination of both were deposited by using wet-impregnation or co-impregnation methods to make the V₂O₅/TiO₂–ZrO₂, CeO₂/TiO₂–ZrO₂ and V₂O₅–CeO₂/TiO₂–ZrO₂ combination catalysts, respectively. These catalysts were characterized using X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature preprogrammed reduction (TPR), CO₂ temperature preprogrammed desorption (TPD) and BET surface area methods. All characterization studies revealed that the deposited promoter oxides are in a highly dispersed form over the support, and the combined acid–base and redox properties of the catalysts play a major role in this reaction. The V₂O₅–CeO₂/TiO₂–ZrO₂ catalyst exhibited a better conversion and product selectivity than other combinations. In particular, the addition of CeO₂ to V₂O₅/TiO₂–ZrO₂ prevented catalyst deactivation and helped to maintain a high and stable catalytic activity.     

Coking kinetics of a Cr2O3/Al2O3 catalyst during 1-butene dehydrogenation: Effect of H2 partial pressure

The influence has been studied of the partial pressure of hydrogen (0–30 kPa) upon the coking rate of a Cr₂O₃/Al₂O₃ commercial catalyst during 1-butene dehydrogenation. Coke deposition has been analysed using a monolayer-multilayer reversible coke growth model (MMRC model). This model provides good fits to the experimental data, within the range of partial pressure of H₂ studied, and allows us to estimate the main kinetic parameters involved in the coking-deactivation process. The results obtained reveal a dual effect of hydrogen: competition against 1-butene for the active sites and the removal of coke precursors from the catalyst surface. Bom effects diminish the coking rate as the H₂ partial pressure is increased.     

Kinetics of oxidative cracking of n‐hexane to olefins over VOx/Ce‐Al2O3 under gas phase oxygen‐free environment

The kinetics of oxidative cracking of n‐hexane to olefins using lattice oxygen of VO_x/Ce‐Al₂O₃ is investigated. The TPR/TPO analysis shows a consistent reducibility (79%) of VO_x/Ce‐Al₂O₃ in repeated redox cycles. The total acidity of the sample is found to be 0.54 mmol/g with 22% are strong acid sites that favors olefin selectivity. The oxidative cracking of n‐hexane in a fluidized CREC Riser simulator gives approximately 60% olefin selectivity at 30% n‐hexane conversion. A kinetic model is developed considering (1) cracking, (2) oxidative dehydrogenation (ODH), and (3) catalyst deactivations. The proposed cracking mechanism considers adsorption, C–H and C–C bond fission and desorption as elementary steps and implemented by pseudo steady state hypothesis. A Langmuir‐Hinshelwood mechanism is found to represent the ODH reactions. The developed model fits the experimental data with favorable statistical indicators. The estimated specific reaction rate constants are also found to be consistent with the product selectivity data. © 2016 American Institute of Chemical Engineers AIChE J, 63: 130–138, 2017     

Comparison of a new immobilized Fe3+ catalyst with homogeneous Fe3+–H2O2 system for degradation of 2,4‐dinitrophenol

BACKGROUND: Heterogeneous Fenton catalysts have been used to treat various organic pollutants in an aqueous environment. The present study has investigated the degradation of 2,4‐dinitrophenol (2,4‐DNP), a priority pollutant generated by such industries as pharmaceuticals, pesticides, pigments and dyes. Degradation of 2,4‐DNP (100 mg L^?1) was studied using Fe³⁺ loaded on Al₂O₃ as a heterogeneous catalyst in the presence of H₂O₂, and the efficiency compared with the homogeneous Fe³⁺/H₂O₂ based Fenton‐like process. The effect of different parameters for both processes, such as catalyst loading, H₂O₂ concentration, initial solution pH, initial substrate concentration and temperature were investigated and the optimum operating conditions determined. RESULTS: Under optimal operating conditions of the homogeneous system ([Fe³⁺] 125 mg L^?1; [H₂O₂] 250 mg L^?1; pH 3; room temperature), 92.5% degradation was achieved in 35 min for an initial 2,4‐DNP concentration of 100 mg L^?1. In the case of immobilized Fe (Fe³⁺–Al₂O₃ catalyst), degradation improved to 98.7% under the condition 10 wt% [Fe³⁺–Al₂O₃] 1 g L^?1 catalyst loading; [H₂O₂] 250 mg L^?1; pH 3; at room temperature for the same duration. CONCLUSIONS: This study demonstrated the stability and reusability of the prepared heterogeneous catalyst. This process is a viable technique for treatment of aqueous solutions containing contaminants. Copyright © 2012 Society of Chemical Industry     

Oxidative dehydrogenation of ethylbenzene to styrene with CO2 over SnO2–ZrO2 mixed oxide nanocomposite catalysts

SnO₂–ZrO₂ nanocomposite catalysts with different compositions ranging from 0 to 100% of SnO₂ were prepared at room temperature by co-precipitation method using aqueous ammonia as a hydrolyzing agent. X-ray diffraction, transmission electron microscopic characterization revealed the SnO₂–ZrO₂ nanocomposite behavior. Acid–base properties of these catalysts were ascertained by temperature-programmed desorption (TPD) of NH₃ and CO₂. Both acidic and basic sites distribution of the nanocomposite catalysts is quite different from those of respective single oxides (SnO₂ or ZrO₂). Catalytic activity of these nanocomposite catalysts for ethylbenzene dehydrogenation (EBD) to styrene in the presence of excess CO₂ was evaluated. The change in the acid–base bi-functionality of the nanocomposite catalysts in comparison with single oxides had profound positive influence in enhancing the catalytic activity.     

Influence of technological parameters on the epoxidation of 1‐butene‐3‐ol over titanium silicalite TS‐2 catalyst

BACKGROUND: The influence of technological parameters on the epoxidation of 1‐butene‐3‐ol (1B3O) over titanium silicalite TS‐2 catalyst has been investigated. Epoxidations were carried out using 30%(w/w) hydrogen peroxide at atmospheric pressure. The major product from the epoxidation of B3O was 1,2‐epoxybutane‐3‐ol, with many potential applications. RESULTS: The influence of temperature (20–60 °C), 1B3O/H₂O₂ molar ratio (1:1–5:1), methanol concentration (5–90%(w/w)), TS‐2 catalyst concentration (0.1–6.0%(w/w)) and reaction time (0.5–5.0 h) have been studied. CONCLUSION: The epoxidation process is most effective if conducted at a temperature of 20 °C, 1B3O/H₂O₂ molar ratio 1:1, methanol concentration (used as the solvent) 80%(w/w), catalyst concentration 5%(w/w) and reaction time 5 h. Copyright © 2009 Society of Chemical Industry     

Selective oxidation and ammoxidation of propane on a Mo–V–Te–Nb–O mixed metal oxide catalyst: a comparative study

A comparative study on the selective oxidation and the ammoxidation of propane on a Mo–V–Te–Nb–O mixed oxide catalyst is presented. The catalyst has been prepared hydrothermally at 175 °C and heat-treated in N₂ at 600 °C for 2 h. Catalyst characterization results suggest the presence mainly of the orthorhombic Te₂M₂₀O₅₇ (M = Mo, V and Nb) bronze in samples before and after use in oxidation and ammoxidation, although some little modifications have been observed after its use in ammoxidation reaction. Propane has been selectively oxidized to acrylic acid (AA) in the 340–380 °C temperature range while the ammoxidation of propane to acrylonitrile (ACN) has been carried out in the 360–420 °C temperature interval. The steam/propane and the ammonia/propane molar ratios have an important influence on the activity and the selectivity to acrylic acid and acrylonitrile, respectively. The reaction network in both oxidation and ammoxidation reactions as well as the nature of active and selective sites is also discussed. The catalytic results presented here show that the formation of both ACN and AA goes through the intermediate formation of propene.