Catalytic Combustion Of Propane Research Articles

Modulation mechanism of Mn-O strength in α-MnO2 catalyst for high-efficiency catalytic combustion of propane

The cleavage of C-H with high energy impedes the catalytic combustion of propane. Herein, α-MnO2 with modulation of Mn-O strength by changing the calcination temperature was applied in propane catalytic combustion. α-MnO2 calcinated at 350 °C (α-MnO2-350) exhibited superior performance (T20=150 °C, T90= 220 °C) in propane oxidation due to the synergistic effect of oxygen vacancies (OVs) and Lewis acidity. Density functional theory (DFT) calculations revealed that the lowest o-vacancy formation energy on α-MnO2-350 (Evo=0.74 eV) with its lowest Mn-O strength prompted the existence of abundant OVs and propane oxidation. Moreover, the highest Lewis acidity in α-MnO2-350 displayed the strongest propane adsorption, promoting the activation of C-H. The mineralization of propane on α-MnO2-350 dropped steeply after 68 h while could recover to 90 % in long-term water vapor stability test owing to the H2O adsorbed at OVs and the carbonaceous intermediates adsorbed at the Lewis acid sites.

CO and Propane Combustion on La0.8Sr0.2CoxFe1−xO3−δ Perovskites: Effect of Fe-to-Co Ratio on Catalytic Activity

Perovskites are promising alternative catalysts for oxidation reactions due to their lower cost compared to noble metals, and their greater thermal stability. The catalytic oxidation of CO is essential in order to control CO emissions in a series of applications whereas the catalytic combustion of propane is considered an economical and environmentally acceptable solution for energy production and gaseous pollutant management, since propane is among the organic compounds involved in photochemical reactions. This work concerns the effect of the Co/Fe ratio in the B-sites of a series of eight La0.8Sr0.2CoxFe1−xO3−δ perovskites, with x ranging from 0 to 1, on the catalytic activity towards CO and C3H8 oxidation. The perovskite oxides were synthesized using the combustion synthesis method and characterized with respect to their specific surface areas, structures, and reduction properties. Increasing the Co/Fe ratio resulted in an increase in CO and propane conversion under both oxidative and stoichiometric conditions. The increase in Co content is considered to facilitate the formation of oxygen vacancies due to the lower redox stability of the cobalt cations compared to iron cations, favoring oxygen ion mobility and oxygen exchange between the gas phase and the oxide surface, thus enhancing the catalytic performance.

Mo-modified Pt/CeO2 nanorods with high propane catalytic combustion activity: Comparison of phosphoric, sulphuric and molybdic acid modifications

Catalytic combustion is the most commonly used reaction to purify VOCs. The activation and dissociation of the CH bond over the catalyst becomes a key factor in controlling the rate of the reaction. To identify the factors promoting CH bond decomposition and the roles played by the acidity of the catalyst in propane catalytic combustion, molybdic acid, phosphoric acid, and sulfuric acid were used to acidify CeO2 nanorods, and Pt was then loaded onto the nanorods. The Mo acid modified Pt/CeO2 catalyst purified more than 90% of propane at a high space velocity of 150,000 mL/(g·h) and 300 °C, which is a significant improvement over the Pt/CeO2 catalyst. XRD patterns and TEM images showed that the crystal structure and morphology of CeO2 were not damaged by acid modification. XPS, in situ CO-DRIFTs, NH3-TPD, H2-TPR and other characterization methods were used on Mo acid modified catalysts to explore the reasons for the improved catalytic performance. The results showed that Pt2+ and Pt4+ coexist on 1% Pt/CeO2-18Mo catalyst, and there are more acidic sites, redox sites and adsorbed oxygen. The reaction order test showed the reaction order of molybdic acid modified catalyst to oxygen is -0.4, which is higher than other catalysts, meaning that oxygen is difficult to inhibit the reaction on the catalyst surface. Finally, in situ DRIFTs proved that 1% Pt/CeO2-18Mo catalyst had strong propane adsorption and activation capacity. This catalyst provides new insight into how VOCs can be eliminated more efficiently, green and economically.

Catalytic combustion of propane over Mg-modified Co1.5Mn1.5O4 spinel catalysts: Boosting C-H cleavage with Lewis acid and oxygen vacancies

Rational modulation of surface electronic structure can optimize the adsorption and activation of reactant molecules on the catalyst surface, which is crucial for catalytic elimination of hydrocarbons. Herein, a facile low-valence Mg doping strategy was applied to synthesize highly active and stable Co-Mn binary oxide (CMO) catalyst. Lewis acid sites and oxygen vacancies were purposefully introduced on CMO through the surface electron deficit caused by the substitution of doped Mg for host metals. For the CMO catalyst modified by appropriate amount of Mg (CMO-Mg0.05), the Co-Mn spinel with lattice expansion is significantly modified through substitution of Co or Mn ions with Mg2+, resulting in generation of abundant higher metal oxidation state species (Co3+, Mn4+) and oxygen vacancies. The best performance for catalytic propane combustion was achieved on CMO-Mg0.05 catalyst, with the T90 at 255 °C under high space velocity (60,000 ml g−1 h−1). Meanwhile, clear improvements on stability and water resistance were also achieved after the modification of Mg in CMO catalyst. Combined with C3H8-TPD, in-situ DRIFTS and various characterizations, it can be revealed that the synergistic effect of Lewis-acid sites and oxygen vacancies would remarkably promote the process of propane dissociative adsorption and mineralization. This work not only gives insight into the Mg dopants in boosting CH activation on CMO catalyst, but also provides a potential strategy for fabricating highly active hydrocarbon combustion catalysts.

Catalytic Combustion of Propane over Ce-Doped Lanthanum Borate Loaded with Various 3d Transition Metals

Ce-doped LaBO3 (Ce0.05La0.95BO3) and a corresponding incorporation with 3d transition metals (TMs) were prepared and evaluated for eliminating propane. Our results showed the catalytic activity toward propane combustion has a close relationship with the loaded TMs, which promoted oxygen vacancies density and further enhanced the reduction and acidity of this material. This eventually led to 90% propane conversion at 718 K for a Cu-loaded Ce0.05La0.95BO3 catalyst. During 10 h of catalytic propane oxidation, the propane-elimination rate was maintained very well, with no degradation of the catalyst.

A simple model catalyst study to distinguish the roles of different oxygen species in propane and soot combustion

It is important yet difficult to distinguish the specific roles of superficial Oxn- and interfacial lattice oxygen in catalytic combustion, especially over catalysts consisting of reducible metal oxides. In this study, based on the comparison of two natural counterparts with similar structure — CeO2 (an Oxn- generator) and Pr6O11 (a lattice oxygen contributor), it is suggested that the catalytic combustion of propane under lean-burn conditions followed a typical Mars-van Krevelen mechanism, in which catalyst lattice oxygen represented the dominant reactive phases while superficial Oxn- played negligible roles. As for soot combustion, adsorbed Oxn- represented more sustainable oxidants than lattice oxygen (drained easily at the beginning of the reactions). Such a comparison is readily achieved and widely applicable, which may shed light on the identification of dominant reactive phases for various oxidation reactions over oxide-based catalysts.

Effects of the Reaction Parameters and Light Hydrothermal Aging for Catalytic Combustion of Propane over Co-Mn-Ce Catalyst

A composite oxides’ Co-Mn-Ce catalyst was synthesized by a coprecipitation method, and the experiment was carried out to study the effects of reaction parameters and light hydrothermal aging on propane combustion over the Co-Mn-Ce catalyst. The influence of reaction temperature, propane concentration, oxygen concentration, water vapor, and hydrothermal aging was studied during the catalytic combustion of propane. The propane conversion significantly decreased by 10% when the propane concentration increased at 300°C and then further decreased from 80% to 40% as water vapor concentration increased from 0 to 10 vol.%. In addition, water vapor also prolonged the time required to reach equilibrium. After hydrothermal treatment, the catalyst obtained the lowest oxidation capacity of propane. Furthermore, the results of in situ DRIFTs and O2 temperature programmed desorption (O2-TPD) demonstrated that there were fewer oxygen species after hydrothermal aging, and carbonates were the main intermediates formed during the catalytic oxidation of propane.

Effects of catalyst preparation methods on the performance of La2MMnO6 (M=Co, Ni) double perovskites in catalytic combustion of propane

Effects of catalyst preparation methods on the performance of La2MMnO6 (M=Co, Ni) double perovskites in catalytic combustion of propane

Surface Modification of Cobalt‐Manganese Mixed Oxide and Its Application for Low‐Temperature Propane Catalytic Combustion

AbstractThe Co−Mn mixed metal oxide was firstly fabricated using Co(NO3)2, KMnO4 and K2CO3. The tuned catalysts, donated as xM‐Co3Mn1 (x=0, 0.025, 0.05 and 0.1), were synthesized by selective dissolve method (SD). The physicochemical properties induced by different acid concentrations on catalysts were explored via a series of characterization techniques. Compared with the original material, the catalysts treated by SD had higher advantages in enriching crystal defects, surface Co2+ and adsorbed oxygen species as well as increasing the specific surface areas (SSA). Among acid‐treated catalysts, 0.05 M‐Co3Mn1 exhibited the best catalytic activity, while the T50 and T90 were 71 and 117 °C lower than the original one. Meanwhile, 0.05 M‐Co3Mn1 showed excellent stability and great regeneration ability.

Catalytic Combustion of Propane over Pt-Mo/ZSM-5 Catalyst: The Promotional Effects of Molybdenum

To improve propane combustion activity and illustrate the promotional effects of molybdenum doping, Pt-Mo/ZSM-5 catalysts with different Mo amounts were prepared by the co-impregnation method. XRD, Raman, H2-TPR, NH3-TPD, in situ DRIFTs, XPS and other characterizations were performed. The results indicated that the concentration of Pt0 in Pt/ZSM-5 catalyst increased after the doping of Mo and the content of Pt0 had a positive correlation with the reaction turnover frequency value. The propane combustion activity of Pt/ZSM-5 catalyst was significantly improved after the doping of molybdenum species. Among all the catalysts, Pt-6Mo/ZSM-5 catalyst (Pt/ZSM-5 with 6 wt.% Mo modification) showed the lowest T50 and T90 for propane catalytic combustion. Moreover, the Pt-Mo/ZSM-5 catalyst exhibited outstanding catalytic stability.

Catalytic combustion of propane on Pd-modified Al–La–Ce catalyst – from reaction kinetics and mechanism to monolithic reactor tests and scale-up

Abstract A propane combustion catalyst was prepared by supporting of Pd on optimized multiphase composition, containing Al2O3, La2O3 and CeO2 aiming for possible application in catalytic converters for abatement of propane in waste gases. The catalyst characterization has been made by N2- physisorption, XRD, SEM/EDX, TEM and XPS. The obtained values for reaction order towards propane and oxygen are 0.57 and 0.14, respectively. The negative reaction order towards the water vapour (−0.26) shows an inhibition effect of the water molecules. According to the kinetics model calculations, the reaction pathway over Pd-modified La–Ce catalyst proceeds most probably through Langmuir–Hinshelwood mechanism with adsorption of propane and oxygen on different types of sites, dissociative adsorption of oxygen, whereupon water molecules compete with propane molecules for one and the same type of adsorption sites. For practical evaluation of the synthesized material, a sample of Pd/Al2O3–La2O3–CeO2, supported on rolled Al-containing stainless steel (Aluchrom VDM®) to form a single monolithic channel was prepared and tested. Two-dimensional heterogeneous models were used to simulate the propane combustion from laboratory reactor to full-scale adiabatic monolithic converter for ensuring an effective abatement of propane emissions.

Sol–gel citrate procedure to synthesize Ag/Co3O4 catalysts with enhanced activity for propane catalytic combustion

The Co3O4 and Ag/Co3O4 catalysts with varying content of Ag were fabricated via sol–gel citrate procedure, which were used for propane total oxidation. First, Ag+ and/or Co2+ ions coordinate with citric acid to form silver and/or cobalt citrate complex, then calcined to produce Ag/Co3O4 catalysts. Among all the catalysts, the 6%Ag/Co3O4 sample exhibited a much higher catalytic performance, with 90% conversion of propane at only 228 °C, which was 24 °C lower than that of pure Co3O4 catalyst. Characterization results showed that the introduction of Ag decreased the particle size of Co3O4, increased the Co3+/(Co3++Co2+) ratio and surface adsorption oxygen content, and enhanced the low-temperature reducibility, which resulted in the outstanding catalytic performance.

Preparation of Ag-Mn/γ-Al2O3-TiO2 catalysts by complexation-impregnation process with citric acid and its application in propane catalytic combustion

A series of Ag-Mn/γ-Al2O3-TiO2 catalysts were prepared by different impregnation procedures. The catalysts were characterized by BET, XRD, TEM, XPS and H2-TPR, and the catalytic properties were investigated by propane catalytic combustion. Results show that compared with the conventional impregnation method, complexation-impregnation procedure with citric acid promotes the dispersion of Ag and Mn particles on the surface of catalyst and strengthens the interaction between Ag and Mn, so as to increase the relative content of reactive oxygen species and improve the reducibility of catalysts, which further improves the catalytic activity of propane combustion reaction. Especially, the Ag1Mn3/γ-Al2O3-TiO2 catalyst prepared by complexation-impregnation process with citric acid exhibits the best activity for propane catalytic combustion with 90% conversion at 263°C.

Modeling the propane combustion process within a micro-catalytic porous combustor by using the lattice Boltzmann method

Understanding the micro-catalytic porous combustion mechanisms is vital importance in improving the energy conversion efficiency of a combustion process. However, the investigation on this issue is still challenging due to the complex multiple physicochemical and thermal coupled transport mechanisms occurring in this process. In this work, a coupled lattice Boltzmann model is developed for modeling propane catalytic combustion process within a micro-catalytic porous combustor, in which the coupled transport mechanisms including multi-component gases flow, mass and heat transfers, as well as the heterogeneous catalytic combustion reaction are fully considered. Then, a systematic analysis regarding operating conditions and pore structure parameters was performed to disclose the micro-catalytic porous combustion mechanisms and dominated factors in determining the conversion efficiency. Results show that the conversion efficiency of propane in the micro-catalytic porous combustor majorly depends on the equivalence ratio, gas temperature and support materials properties. With an increment of the equivalence ratio, the conversion efficiency was improved firstly and then reduced, and an optimal combustion performance can be achieved where the equivalence ratio is equal to the chemical equivalent value. As the gas temperature increases, the conversion efficiency rises tremendously. To achieve a desirable combustion performance, the high gas temperature (> 700 K) should be maintained. Moreover, the support materials change the heat transfer and heat loss of the combustor, and the support materials with a low thermal conductivity or thermal diffusivity can reduce the heat loss and therefore enhance the conversion efficiency.

Total Oxidation of Propane over a Ru/CeO2 Catalyst at Low Temperature.

Ruthenium (Ru) nanoparticles (∼3 nm) with mass loading ranging from 1.5 to 3.2 wt % are supported on a reducible substrate, cerium dioxide (CeO2, the resultant sample is called Ru/CeO2), for application in the catalytic combustion of propane. Because of the unique electronic configuration of CeO2, a strong metal-support interaction is generated between the Ru nanoparticles and CeO2 to stabilize Ru nanoparticles for oxidation reactions well. In addition, the CeO2 host with high oxygen storage capacity can provide an abundance of active oxygen for redox reactions and thus greatly increases the rates of oxidation reactions or even modifies the redox steps. As a result of such advantages, a remarkably high performance in the total oxidation of propane at low temperature is achieved on Ru/CeO2. This work exemplifies a promising strategy for developing robust supported catalysts for short-chain volatile organic compound removal.

Catalytic combustion of propane over mixed oxides derived from CuxMg3−xAl hydrotalcites

Cu-based mixed oxides (CuxMg3−xAlO-800s, x=0, 0.5, 1.0, 1.5, 2.0 and 3.0) were prepared by calcinations of corresponding CuxMg3−xAl ternary hydrotalcites (CuxMg3−xAl-HTLCs) at 800°C and used for catalytic combustion of propane. The CuxMg3−xAl ternary hydrotalcites and derived combustion catalysts were well characterized to investigate the dependence of the performance of propane catalytic combustion with their structure and components. The results showed that Cu can replace Mg in a wide range of Cu/Mg ratios to form CuxMg3−xAl-HTLCs with the unique layered structure of hydrotalcite, though the Cu substitution significantly deteriorates the thermal stability of the CuxMg3−xAl-HTLCs. It was found that calcinations at 800°C completely transformed the CuxMg3−xAl-HTLCs to CuxMg3−xAlO-800 mixed oxides, containing spinel, periclase and tenorite oxide phases. The TPR results revealed those catalysts derived from hydrotalcites were easier to be reduced than the simply mixed oxides, this was due to the strong interactions among the components existing in the CuxMg3−xAlO-800 materials. The CuxMg3−xAlO-800 catalysts exhibit superior catalytic activity in propane combustion to Pd/Al2O3 and the mechanically mixed oxides. The excellent activities of the CuxMg3−xAlO-800 were attributed to the strong interaction among the component oxides as observed by the XRD, TG-DSC and TPR characterizations.

Dry citrate-precursor synthesized nanocrystalline cobalt oxide as highly active catalyst for total oxidation of propane

A set of nanocrystalline cobalt oxide (Co 3O 4)-based catalysts have been prepared by means of an innovative soft reactive grinding (SRG) procedure. The catalysts exhibited excellent activities and high stabilities for propane catalytic combustion. Complete conversion has been achieved at reaction temperatures as low as 240 °C. Comparing with the highly active Co 3O 4 catalysts in the current literature, the catalysts in this work show exceptionally high specific rate for propane total oxidation (ca. 91.3 mmol C 3 m − 2 h − 1 at 200 °C). A correlation between the O 2-TPD results and the activity for Co 3O 4 reveals that a high concentration of superficial electrophilic oxygen (O −) species is important for achieving a high activity. The prominent lattice distortion induced by prolonged citrate-precursor grinding is suggested to play a key role in creating and maintaining a high density of surface defects, which leads to highly activity and stability of the cobalt spinel catalyst.

Stability and performance of catalytic microreactors: Simulations of propane catalytic combustion on Pt

A pseudo-two-dimensional (2D) model is developed to analyze the operation of platinum-catalyzed microburners for lean propane–air combustion. Comparison with computational fluid dynamics (CFD) simulations reveals that the transverse heat and mass transfer is reasonably captured using constant values of Nusselt and Sherwood numbers in the pseudo-2D model. The model also reasonably captures the axial variations in temperatures observed experimentally in a microburner with a 300 μ m gap size. It is found that the transverse heat and mass transport strongly depend on the inlet flow rate and the thermal conductivity of the burner solid structure. The microburner is surface reaction limited at very low velocities and mass transfer limited at high velocities. At intermediate range of velocities (preferred range of reactor operation), mass transfer affects the microburner performance strongly at low wall conductivities, whereas transverse heat transfer affects stability under most conditions and has a greater influence at high wall conductivities. At sufficiently low flow rates, complete fuel conversion occurs and reactor size has a slight effect on operation (conversion and temperature). For fast flows, propane conversion strongly depends on residence time; for a reactor with gap size of 600 μ m , a residence time higher than 6 ms is required to prevent propane breakthrough. The effect of reactor size on stability depends on whether the residence time or flow rate is kept constant as the size varies. Comparisons to homogeneous burners are also presented.

Application of a CFD Code (FLUENT) to Formulate Models of Catalytic Gas Phase Reactions in Porous Catalyst Pellets

A method is described by which a CFD code known as FLUENT, may be adapted to model the reactions that take place inside catalyst structures. To test the CFD code, simulations of gas flow in a circular tube are performed and compared with analytical solutions. Then the coupled processes of diffusion and chemical reaction, combined with heat and mass transfer effects are modelled in a catalyst pellet. To illustrate the technique, the catalytic combustion of propane is simulated in spherical and cylindrical shaped pellets, at gas temperatures from 500 to 700 K and at atmospheric pressure. To help validate the approach adopted, the results of the CFD simulations are compared with solutions obtained from a one-dimensional model using MATLAB. It is shown that the CFD simulations provide comparable results with MATLAB, and that the CFD code can provide valuable additional information about temperature and concentration gradients in and around the catalyst pellet—this is not available in a simple one-dimensional approach. It is discussed how the technique could be extended to model reactions in a packed bed which would be a valuable design tool.

05/02815 CFD simulation of the effect of upstream flow distribution on the light-off performance of a catalytic converter

A method is described by which a CFD code known as FLUENT, may be adapted to model the reactions that take place inside catalyst structures. To test the CFD code, simulations of gas flow in a circular tube are performed and compared with analytical solutions. Then the coupled processes of diffusion and chemical reaction, combined with heat and mass transfer effects are modelled in a catalyst pellet. To illustrate the technique, the catalytic combustion of propane is simulated in spherical and cylindrical shaped pellets, at gas temperatures from 500 to 700 K and at atmospheric pressure. To help validate the approach adopted, the results of the CFD simulations are compared with solutions obtained from a one-dimensional model using MATLAB. It is shown that the CFD simulations provide comparable results with MATLAB, and that the CFD code can provide valuable additional information about temperature and concentration gradients in and around the catalyst pellet—this is not available in a simple one-dimensional approach. It is discussed how the technique could be extended to model reactions in a packed bed which would be a valuable design tool.