Simple method for the simultaneous evaluation of combustion and selective oxidation catalysts

The conventional rapid combustion technique used for microanalysis of organic compounds has been modified for the simultaneous evaluation of combustion and selective oxidation catalysts. Using this technique, MnO₂ has been confirmed to be a good combustion catalyst. It was also possible to conclude that Fe₂O₃ and V₂O₅ are good selective oxidation catalysts at 250°C and 300°C, respectively. This simple and rapid method offers much scope for probing into the mechanism of oxidation of hydrocarbons.     

Catalytic oxidation of hydrogen over Au/TiO2 catalysts

Selective catalytic oxidation of hydrogen in the presence of hydrocarbons was studied in a fixed bed quartz reactor, over 3 wt%Au/TiO₂ and 5 wt%Au/TiO₂ catalysts. This reaction can be utilised in the production of light alkenes via catalytic dehydrogenation, providing in situ heat to the endothermic dehydrogenation reaction and simultaneously removing a fraction of the produced hydrogen. It is important to avoid the non-selective combustion of the hydrocarbons in the mixture. Both 3 wt%Au/TiO₂ and 5 wt%Au/TiO₂ are active for the combustion of hydrogen, but in a gas mixture with propane and oxygen the selectivity is dependent upon the feed ratio of hydrogen and oxygen. At 550 °C, with propane present, no carbon oxides are formed when the H₂:O₂ ratio is four, but at lower ratios some CO₂ and some CO is formed.     

基于化学链燃烧的吸收剂引导的焦炉煤气水蒸气重整制氢过程模拟

建立了基于化学链燃烧供能的吸收剂引导的焦炉煤气水蒸气重整制氢系统,该系统包含吸收剂引导的焦炉煤气重整反应器（SECOGSR）、燃料反应器和空气反应器。该系统能产生高纯H₂［93.23%（mol）］,仅通过冷凝即可实现CO₂的捕获,分离能耗低。采用Aspen Plus软件对吸收剂引导的焦炉煤气重整制氢过程进行了模拟,得到优化的反应条件为：温度650℃,压力1.5 MPa,Ca/C=1,H₂O/C=4。并对系统进行了模拟,以NiO/Y₂O₃/ZrO₂(0.73/0.022/0.248,摩尔比）为化学链燃烧的载氧体和载能体,在满足反应器自热平衡和系统吸放热平衡的基础上,重整1mol焦炉煤气,燃料反应器和空气反应器所需的焦炉煤气、空气及载氧体NiO/Y₂O₃/ZrO₂的量分别为0.139、0.648、3.11 mol。该系统消耗1 mol焦炉煤气的产H₂量为1.30 mol,捕获的CO₂的量为0.355 mol。     

Iron—molybdenum—oxide catalysts for selective oxidation of hydrogen sulfide to sulfur

The selective oxidation of hydrogen sulfide to sulfur was studied over iron-molybdenum oxides with various Fe-Mo ratios. Strong synergistic phenomenon in catalytic activity was observed for the Fe-Mo-O binary oxides. Under identical reaction conditions, the areal rates of the binary oxides were superior to those of the corresponding single oxide catalysts, which suggest that the new compound Fe₂(MO₄)₃ formed in the binary oxide is more active than Fe₂O₃ and MoO₃. The oxidation rates of H₂S were found to exhibit first-order dependence on the hydrogen sulfide concentration, which implies that the activation of H₂S is the rate-limiting step.     

Thermal oxidation of iron nanoparticles and its implication for chemical‐looping combustion

BACKGROUND: Chemical looping combustion (CLC) is a promising environmentally friendly technology in which the greenhouse gas CO₂ can be readily separated at high‐purity, therefore providing an effective method of carbon capture. Its performance, however, is limited by the kinetics of oxidation of the oxygen carrier, whose size is typically in the range of micrometers to millimetres. This paper reports a new idea using metallic nanoparticles as potential oxygen carriers to improve the performance of chemical looping combustion. RESULTS: A detailed experimental study of the heating and oxidation of iron nanoparticles in a simultaneous TGA/DSC system was conducted. Kinetic analysis revealed improved reactivity of iron nanoparticles, as shown by a reduction in the activation energy, which is highly dependent upon the conversion ratio. The implication and potential application of nanoscale metallic nanoparticles as oxygen carriers in CLC are discussed. CONCLUSION: Compared with conventional sized iron particles, the reduction of particle size to nanoscale can offer a number of advantages, such as increased reactivity, reduced mass resistance and enhanced heat transfer, however, a number of practical factors associated with increased specific surface area need to be assessed carefully. Copyright © 2010 Society of Chemical Industry     

Fe‐substituted Ba‐hexaaluminates oxygen carrier for carbon dioxide capture by chemical looping combustion of methane

Fe‐substituted Ba‐hexaaluninates (BFA‐x (x = 1–3), x indicates Fe content) oxygen carrier (OC) were found to exhibit excellent sintering‐resistance under cyclic redox atmosphere at 800°C thanks to the reservations of the structure during the CH₄ reduction step, thus preventing the agglomeration of particles during the subsequent reoxidation step. Lattice oxygen highly active for the total combustion of CH₄ was observed in the hexaaluminate structure and its chemical state was influenced by Fe content. The highest amount of active O coordinated with Fe³⁺ in the mirror plane (O‐Fe³⁺(M)) for the total combustion was reacted (0.77 mmol/g) for BaFe₃Al₉O₁₉ hexaaluminate OC. As a result, it exhibited the best reactivity with the CH₄ conversion of 83% and CO₂ selectivity of 100%. Moreover, superior regeneration and recyclability was also obtained, which originated from the fully recovery of O‐Fe³⁺(M) in the hexaaluminate structure. © 2015 American Institute of Chemical Engineers AIChE J, 62: 792–801, 2016     

以蜂窝陶瓷为载体的燃烧催化剂研究

采用蜂窝状载体,在蜂窝陶瓷基质上涂以助剂,制备了Pt-Pd为活性组分催化剂,考察了催化剂对CO、HC的净化效果及蜂窝催化剂的耐热性能。结果表明,添加助剂对催化剂的活性有很大的影响,可使HC的催化燃烧活性得到显著的提高;相对于无助剂催化剂,其丙烯的最低全转化温度降低了70℃。表明蜂窝Pt-Pd,助剂/A l2O3是一个很有应用潜力的低温烃类燃烧贵金属催化剂。     

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%.     

Reduction kinetics of a fluidizable nickel–alumina oxygen carrier for chemical‐looping combustion

This study investigates the kinetic modelling of oxygen carrier reduction by methane in the combustion reactor of the chemical‐looping combustion process. The species being reduced and the stability of the fluidizable oxygen carrier sample over repeated reduction–oxidation cycles are established using the temperature programmed reduction and oxidation and the pulse chemisorption characterization methods. The power‐law relation, the nucleation and nuclei growth model and the shrinking‐core models are considered to interpret the experimental kinetics of the oxygen carrier reduction. The obtained results show that the nucleation and nuclei growth model best describes the experimental data providing parameters with adequate statistical fitting indicators.     

Modeling of propane dehydrogenation combined with chemical looping combustion of hydrogen in a fixed bed reactor

A redox process combining propane dehydrogenation(PDH) with selective hydrogen combustion(SHC) is proposed, modeled, simulated, and optimized. In this process, PDH and SHC catalysts are physically mixed in a fixed-bed reactor, so that the two reactions proceed simultaneously. The redox process can be up to 177.0% higher in propylene yield than the conventional process where only PDH catalysts are packed in the reactor. The reason is twofold: firstly, SHC reaction consumes hydrogen and then shift...     

Model‐based analysis of chemical‐looping combustion experiments. Part I: Structural identifiability of kinetic models for NiO reduction

To guide the design of chemical‐looping combustion (CLC) systems, the use of accurate models is crucial. The reduction kinetics between NiO and CH₄ is uncertain, in regards to the most suitable kinetic mechanism and reaction network. A framework for structural identifiability analysis is developed and applied to evaluate the candidate kinetic models for the NiO‐CH₄ reaction. The identifiability of kinetic parameters of different model structures is analyzed and compared. Models that lack structural identifiability of their kinetic parameters are rejected in the analysis. From a total of 160 possible candidate models, 4 kinetic models are found to be identifiable with respect to their kinetic parameters and distinguishable from different model structures. This structural identifiability analysis paves the way for model‐based design of experiments, which is the subject of Part II of this work. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2419–2431, 2016     

Fe2O3 on Ce‐, Ca‐, or Mg‐stabilized ZrO2 as oxygen carrier for chemical‐looping combustion using NiO as additive

Oxygen‐carrier particles for chemical‐looping combustion have been manufactured by freeze granulation. The particles consisted of 60 wt % Fe₂O₃ as active phase and 40 wt % stabilized ZrO₂ as support material. Ce, Ca, or Mg was used to stabilize the ZrO₂. The hardness and porosity of the particles were altered by varying the sintering temperature. The oxygen carriers were examined by redox experiments in a batch fluidized‐bed reactor at 800–950°C, using CH₄ as fuel. The experiments showed good reactivity between the particles and CH₄. NiO was used as an additive and was found to reduce the fraction of unconverted CH₄ with up to 80%. The combustion efficiency was 95.9% at best and was achieved using 57 kg oxygen carrier per MW fuel. Most produced oxygen carriers appear to have been decently stable, but using Ca as stabilizer resulting in uneven results. Further, particles sintered at high temperatures had a tendency to defluidize. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

High performance of la‐promoted Fe2O3/α‐Al2O3 oxygen carrier for chemical looping combustion

Iron oxide supported oxygen carrier (OC) is regarded to a promising candidate for chemical looping combustion (CLC). However, phase separation between Fe₂O₃ and supports often occurs resulted from the severe sintering of supports during calcination, which leads to the sintering and breakage of Fe₂O₃ thus the decrease of redox reactivity. In this article, La‐promoted Fe₂O₃/α‐Al₂O₃ were used as OCs for CLC of CH₄ and for the first time found that the OC with the addition of 18 wt % La exhibited outstanding reactivity and redox stability during 50 cycles of CLC of CH₄. Such a superior performance originated from the formation of LaAl₁₂O₁₉ hexaaluminate (La‐HA) phase with not only small particle size but also excellent thermal stability at CLC conditions, which worked as a binder to prevent the phase separation thereby the sintering and breakage of active species α‐Fe₂O₃ were avoided during reaction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2827–2838, 2017     

Multicycle investigation of a sol‐gel‐derived Fe2O3/ATP oxygen carrier for coal chemical looping combustion

Fe‐based oxygen‐carrier particles with attapulgite (ATP) as a support material for coal chemical looping combustion (CLC) have been prepared using a sol‐gel approach. The multiredox characteristics of the prepared Fe4ATP6 (Fe₂O₃ to ATP mass ratio of 40:60) were experimentally examined in a batch fluidized bed reactor at 900°C. The experimental results indicated that the synergistic reactions between ATP and Fe₂O₃ increased the coal conversion. Fe4ATP6 exhibited high reactivity, particularly for low‐rank coals, in the CLC process. The improved pore structure and surface area were responsible for the high reactivity of Fe4ATP6. In 60 redox cycles, H₂ was mainly generated in the outlet gas as the carbon conversion efficiency had reached 95%, and both the coal combustion efficiency and CO₂ capture efficiency were greater than 95%. © 2015 American Institute of Chemical Engineers AIChE J, 62: 996–1006, 2016     

Model‐based analysis of chemical‐looping combustion experiments. Part II: Optimal design of CH4‐NiO reduction experiments

There is significant controversy in the reduction kinetics of chemical‐looping combustion (CLC) between NiO and CH₄. We propose an application of a model‐based framework to improve the quality of CLC experiments with respect to model discrimination and parameter estimation. First, optimal experiments are designed and executed to reject inadequate models and to determine a true model structure for the reaction kinetics of the CH₄‐NiO system. Then, kinetics with statistical significance is estimated from experiments aimed at reducing parameter uncertainty. To maximize the observability of the NiO reduction reactions, fixed bed experiments should exhibit a peak separation of the concentration profiles, an initial high methane slip, and low overall CO₂ selectivity. Several case studies are presented to check the adequacy of the recommended model and evaluate its predictive ability and extrapolation capabilities. The model resulting from this work is validated and suitable for application in process design and optimization. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2432–2446, 2016     

肉桂醛选择性加氢Co-Fe/硅藻土催化剂稳定性考察

通过肉桂醛在高压微反固定床上24 h的催化加氢反应,考察了肉桂醛选择加氢的催化剂Co-Fe/硅藻土稳定性。结果表明,肉桂醛选择加氢催化剂Co-Fe/硅藻土在反应初期存在反应的诱导期,诱导期后,肉桂醛转化率70%,肉桂醇选择性80%,肉桂醇收率可达60%以上,且催化性能趋于平稳,表现出良好的催化性能和稳定性。利用XRD、SEM、TG-DSC对反应前后催化剂结构进行表征,发现催化剂经24 h反应,结构不变,表面颗粒分布更细化,无积炭迹象。     

On the high‐gasification rate of Brazilian manganese ore in chemical‐looping combustion (CLC) for solid fuels

The high rate of char gasification observed when using a Brazilian manganese ore as compared to ilmenite is investigated in a batch fluidized‐bed reactor. Experiments were carried out at 970°C using petroleum coke, coal and wood char as fuel with a 50% H₂O in N₂ as fluidizing gas. A manufactured manganese oxygen carrier was also used, however, which presented a slower char conversion rate than the manganese ore. It is concluded that decrease in H₂ inhibition and oxygen release are unlikely to be the main responsible mechanisms for the ore's unexpected gasification rate. The ore was also mixed in different ratios with ilmenite and it was observed that the presence of even small amounts of ore in the bed resulted in increased gasification rate. Thus, the high‐gasification rate for the manganese ore could be due to a contribution from the impurities in the ore by catalyzing the gasification reaction. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4346–4354, 2013     

Performance of H‐ZSM‐5‐supported bimetallic catalysts for the combustion of polluting volatile organic compounds in air

The performance of H‐ZSM‐5‐supported bimetallic catalysts with chromium as the base metal in the combustion of ethyl acetate and benzene is reported. A reactor operated from 100 to 500 °C at a gas hourly space velocity (GHSV) of 32 000 h^?1 was used for study of the activity. A combination of 1.0 wt% chromium and 0.5 wt% copper yielded a catalyst (Cr_1.0Cu_0.5/Z) with improved conversion and carbon dioxide yield. Cr₂O₃ (Cr³⁺) and CuO (Cu²⁺) were the predominant metal species in the catalyst. In agreement with the Mars–van Krevelen model, improved reducibility of Cr³⁺ in the presence of Cu²⁺ led to an improvement in activity. The copper content in Cr_1.0Cu_0.5/Z also favored the formation of deep combustion products. Condensation and subsequent growth of coke precursors in the catalyst pores led to the formation of a softer and less aromatic coke fraction while dehydrogenation activity on acid sites formed a harder and more aromatic coke fraction. The use of Cr_1.0Cu_0.5/Z favored the formation of lower molecular weight intermediates, leading to reduction in formation of softer coke. Copyright © 2005 Society of Chemical Industry     

γ‐Alumina supported Cu‐Ni bimetallic catalysts: Characterization and selective hydrogenation of 1,3‐butadiene

Addition of a second metal often improves the selectivity of a supported catalyst for the hydrogenation of 1,3‐butadiene. Catalysts containing 15 wt% Ni and varying amounts of Cu were prepared and characterized by TPR, XRD and XPS. The Cu‐Ni interaction affects the reduction behavior of the catalysts. TPR result shows that the synergetic effect of copper and nickel modifies the capability of metal to combine with hydrogen in bulk phase. The Ni 2p spectra in XPS shows significant shifts toward lower binding energies with increasing copper loading. From XRD results it is represented that aggregation of nickel occurs more easily due to the copper addition. The adding of copper on Ni/Al₂O₃ makes the conversion rate decreased and increases the selectivity to 1‐butene.