Low-temperature catalytic combustion of trichloroethylene over MnO_(x)-CeO_(2)mixed oxide catalysts

The cerium-based catalysts were investigated for the catalytic co mbustion of trichlo roethylene(TCE)and exhibit a surprising catalytic activity.MnO_(x)was doped into CeO_(2)by a citric acid(CA)sol-gel method,and the effect of Mn content on the physicochemical properties and catalytic activities of MnO_(x)-CeO_(2)mixed oxides was investigated systemically.The introduction of MnO_(x)into CeO_(2)can evidently improve the catalytic activity and reaction stability of the CeO_(2)catalyst,and the catalytic activity can be maintained for more than 100 h at 250℃under air atmosphere.Moreover,a possible reaction mechanism and a catalytic cycle for the catalytic combustion of TCE over the MnO_(x)-CeO_(2)mixed oxide catalysts are proposed.

Screening non-noble metal oxides to boost the low-temperature combustion of polyethylene waste in air

Globally,the efficient utilization of polymer wastes is one of the most important issues for current sustainable development topics.Herein,a green and efficient low-temperature combustion approach is proposed to deal with polymer wastes and recover heat energy,simultaneously alleviating the environment and energy crisis.Non-noble metal oxides(Al_(2)O_(3),Fe_(2)O_(3),NiO_(2),ZrO_(2),La_(2)O_(3)and CeO_(2)) were prepared,characterized and screened to boost the low-temperature combustion of polyethylene waste at 300℃ in air.The mass change,heat release and CO_(x) formation were studied in details and employed to evaluate the combustion rate and efficiency.It was found that CeO_(2)significantly enhanced the combustion rate and efficiency,which was respectively 2 and 7 times that of non-catalytic case.An interesting phenomenon was observed that the catalytic performance of CeO_(2) in polyethylene low-temperature combustion was significantly improved by the 7-day storage in the room environment or water treatment.XPS analysis confirmed the co-existence of Ce^(3+) and Ce^(4+) in CeO_(2),and the 7-day storage and water treatment promoted the amount of Ce^(3+),which facilitated the formation of the oxygen vacancies.That may be the reason why CeO_(2) exhibited excellent catalytic performance in polyethylene low-temperature combustion.

Catalytic performance and kinetics of Au/γ-Al_2O_3 catalysts for low-temperature combustion of light alcohols

Au/γ-Al2O3 catalysts were prepared by deposition-precipitation method for the catalytic combustion of low concentration alcohol streams(methanol,ethanol,iso-propanol and n-propanol).The catalysts were characterized by X-ray photoelectron spectroscopy(XPS),X-ray diffractometry(XRD) and energy dispersive X-ray micro analysis(EDS) techniques.The XPS results showed that there was only Au0 on the surface of catalysts.The XRD patterns showed that Au was presumably highly dispersed over γ-Al2O3.The temperatures for complete conversion of methanol,ethanol,iso-propanol and n-propanol with concentration of 2.0 g/m3 were 60,155,170 and 137 ℃,respectively,but they were completely mineralized into CO2 and H2O at 60,220,260 and 217 ℃ respectively over the optimized catalyst.The activity of the catalyst was stable in 130 h.The kinetics for the catalytic methanol elimination followed quasi-first order reaction expressed as r=0.652 8c0+0.084 2.The value of apparent activation energy is 54.7 kJ/mol in the range of reaction temperature.

The Fusion Model of Catalytic Combustion and Thermal Conductivity

The further development of catalytic elements has been plagued by activation and binary problems.The automatic shift model that has emerged in recent years helps components achieve full range.However,the detection data still remains unstable in the shift area(7%∼13%).This paper proposes a Catalytic Combustion and Thermal Conductivity(CCTC)model for the specified range,which can be explained fromtwo aspects based on the existing methods.On the one hand,it uses iterative location search to process heterogeneous data,judges the prediction position of data points,and then givesweight evaluation.On the other hand,it corrects the abnormal points,determines the abnormal points in the horizontal direction,and gives the replacement value through the data of adjacent points.The experimental results show that the CCTC model reduces the sum of variance from 17 of the automatic shift model to 13,and the comparison of experimental variance is reduced by 23%.In the full-scale real-time data,the experimental variance of CCTC model and automatic shift model is reduced by 18%.In conclusion,CCTC is a cross section stability framework for full-scale methane measurement,in which the specified heterogeneous combination and anomaly point correction methods improve the stability.

Catalytic combustion of methane over nano ZrO_2-supported copper-based catalysts

The nano ZrO2-supported copper-based catalysts for methane combustion were investigated by means of N2 adsorption, TEM, XRD, H2-TPR techniques and the test of methane oxidation. Two kinds of ZrO2 were used as support, one （ZrO2-1） was obtained from the commercial ZrO2 and the other （ZrO2-2） was issued from the thermal decomposition of zirconium nitrate. It was found that the CuO/ZrO2-2 catalyst was more active than CuO/ZrO2-1. N2 adsorption, H2-TPR and XRD measurements showed that larger surface area, better reduction property, presence of tetragonal ZrO2 and higher dispersion of active component for CuO/ZrO2-2 than that of CuO/ZrO2-1. These factors could be the dominating reasons for its higher activity for methane combustion.

Catalytic combustion of diesel soot over K_2NiF_4-type oxides La_(2-x)K_xCuO_4

Nanostructure K2NiF4 type oxides La2-xKxCuO4 complex oxides were prepared using the Sol-Gel method, characterized by X-Ray Diffraction （XRD）, Fourier Transform Infrared （FT-IR）, and Scanning Electron Microscopy （SEM）. The catalytic activity for soot combustion was evaluated by the Temperature-Programmed Reaction （TPO） technique. The results demonstrated that the substitution quality of K^＋ for La^3＋ at the A-site would increase the catalytic activities of La2-xKxCuO4 for soot combustion greatly; the substitution quality affected the structure and catalytic activity obviously. The La1.8K0.2CuO4 complex oxides with tetrahedral structures had the best catalytic activity for soot combustion, and the ignition temperature of soot combustion was lowered from 490 to 320 ℃.

Preparation and Physicochemical Characterization of La_(1-x)Ce_xCoO_(3+δ) Perovskite Catalyst and Its Methane Catalytic Combustion

Perovskite oxide LaCoO_3 methane catalytic material was synthesized with citric acid complexation and bubbling method. The effect of doped cerium was studied on the series of La_(1-x)Ce_xCoO_(3+δ) materials by means of BET, XRD and SEM techniques. Their catalytic behaviors were studied with methane catalytic complete combustion as probe reaction. The results show that doped cerium has great effect on crystal phase formation. When doped cerium is less than 0.3 ((molar) ratio), the crystal phase of oxide has little changed. When doped cerium is up to 0.5, Co_3O_4 phase is obviously discovered and the perfectibility of LaCoO_3 perovskite crystal phase is deteriorated. When x is over 0.7, perovskite crystal phase is weakened or completely disappeared. Considering the crystal phase of oxides, the optimum doped cerium is about 0.3. The perovskite oxides can be formed at a low calcinations temperature of 700 ℃. When x is 0.3, the highest catalytic activity of T_(10%) (390 ℃) and T_(90%) (603 ℃) is obtained on the series of La_(1-x)Ce_xCoO_(3+δ) materials calcined at 800 ℃.

Influence of chromium modification on the properties of MnO_x-FeO_x catalysts for the low-temperature selective catalytic reduction of NO by NH_3

Catalytic properties of MnOx-FeOx complex oxide （hereafter denoted as Mn-Fe） catalysts modified with different loadings of chromium oxide were investigated by using the combination of physico-cbemical techniques, such as N2 physisorption, X-ray diffraction （XRD）, high-resolution transmission electron microscope （HRTEM）, in situ Fourier transform infrared spectroscopy （in situ FT-IR） and temperature-programmed reduction （TPR） and their catalytic activities were evaluated with the selective catalytic reduction （SCR） of NOx by NH3. It was found that with the addition of Cr, more NO could be removed in the low-temperature window （below 120 ℃）. Among the tested catalysts, Mn-Fe- Cr （2 ： 2 ： 1） catalyst exhibited the best catalytic performance at 80 ℃ with the NO conversion higher than 90%. The combination of the reaction and characterization results indicated that （1） the strong interaction among tertiary metal oxides existed in the catalysts when Cr was appropriately added, which made the active components better dispersed with less agglomeration and sintering and the largest BET specific surface area could be obtained; （2） Cr improved the low-temperature reducibility of the catalyst and promoted the formation of the active intermediate （-NH3＋）, which favored the low-temperature SCR reaction.

Remove cooking fume using catalytic combustion over Pt/La-Al_2O_3

Five monolithic catalysts with low noble metal content were prepared by irnmerge method （Pt/γ=Al2O3, Pt/La-Al2O3, Pt/YSZ-AI203, Pt＋Pd/La-Al2O3 and Pd/La-Al2O3） and their activity measurements were carried out in a conventional fixed-bed flow reactor. The results show that La-Al2O3 can promote activity of the prepared catalysts and can decrease the complete conversion temperature of cooking fume. The Pt/La-Al2O3 catalyst has the highest activity and can be applied in wide range of gas hourly space velocity （GHSV）. Some characterizations （XRD, TPR） were carried out with the objective to explain differences in catalytic behaviors. The prepared catalyst showed a great potential for application.

Recent advances in catalytic combustion of AP-based composite solid propellants

Composite solid propellants(CSPs) have widely been used as main energy source for propelling the rockets in both space and military applications. Internal ballistic parameters of rockets like characteristic exhaust velocity, specific impulse, thrust, burning rate etc., are measured to assess and control the performance of rocket motors. The burn rate of solid propellants has been considered as most vital parameter for design of solid rocket motors to meet specific mission requirements. The burning rate of solid propellants can be tailored by using different constituents, extent of oxidizer loading and its particle size and more commonly by incorporating suitable combustion catalysts. Various metal oxides(MOs),complexes, metal powders and metal alloys have shown positive catalytic behaviour during the combustion of CSPs. These are usually solid-state catalysts that play multiple roles in combustion of CSPs such as reduction in activation energy, enhancement of rate of reaction, modification of sequences in reaction-phase, influence on condensed-phase combustion and participation in combustion process in gas-phase reactions. The application of nanoscale catalysts in CSPs has increased considerably in recent past due to their superior catalytic properties as compared to their bulk-sized counterparts. A large surface-to-volume ratio and quantum size effect of nanocatalysts are considered to be plausible reasons for improving the combustion characteristics of propellants. Several efforts have been made to produce nanoscale combustion catalysts for advanced propellant formulations to improve their energetics. The work done so far is largely scattered. In this review, an effort has been made to introduce various combustion catalysts having at least a metallic entity. Recent developments of nanoscale combustion catalysts with their specific merits are discussed. The combustion chemistry of a typical CSP is briefly discussed for providing a better understanding on role of combustion catalysts in burning rate enhancement. Available information on different types of combustion nanocatalysts is also presented with critical comments.

Progress and key challenges in catalytic combustion of lean methane

As a primary type of clean energy,methane is also the second most important greenhouse gas after CO_(2)due to the high global warming potential.Large quantities of lean methane(0.1–1.0 vol%)are emitted into the atmosphere without any treatment during coal mine,oil,and natural gas production,thus leading to energy loss and greenhouse effect.In general,it is challenging to utilize lean methane due to its low concentration and flow instability,while catalytic combustion is a vital pathway to realize an efficient utilization of lean methane owing to the reduced emissions of polluting gases(e.g.,NOxand CO)during the reaction.In particular,to efficiently convert lean methane,it necessitates both the designs of highly active and stable heterogeneous catalysts that accelerate lean methane combustion at low temperatures and smart reactors that enable autothermal operation by optimizing heat management.In this review,we discuss the in-depth development,challenges,and prospects of catalytic lean methane combustion technology in various configurations,with particular emphasis on heat management from the point of view of material design combined with reactor configuration.The target is to describe a framework that can correlate the guiding principles among catalyst design,device innovation and system optimization,inspiring the development of groundbreaking combustion technology for the efficient utilization of lean methane.

Effects of carrier and Mn loading on supported manganese oxide catalysts for catalytic combustion of methane

Supported manganese oxide catalysts were prepared by incipient wetness impregnation method for methane catalytic combustion, and effects of the support （Al2O3, SiO2 and TiO2） and Mn loading were investigated. These catalysts were characterized with N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed reduction techniques. Methane conversion varied in a large range depending on supports or Mn loading. Al2O3 supported 15% Mn catalyst exhibited better activity toward methane catalytic oxidation. The manganese state and oxygen species played an important role in the catalytic performance,

TiO_2-Supported Binary Metal Oxide Catalysts for Low-temperature Selective Catalytic Reduction of NO_x with NH_3

Binary metal oxide（MnOx-A/TiO2）catalysts were prepared by adding the second metal to manganese oxides supported on titanium dioxide（TiO2）,where,A indicates Fe2O3,WO3,MoO3,and Cr2O3.Their catalytic activity,N2 selectivity,and SO2 poisonous tolerance were investigated.The catalytic performance at low temperatures decreased in the following order：Mn-W/TiO2〉Mn-Fe/TiO2〉Mn-Cr/TiO2〉Mn-Mo/TiO2,whereas the N2 selectivity decreased in the order：Mn-Fe/TiO2〉Mn-W/TiO2〉Mn-Mo/TiO2〉Mn-Cr/TiO2.In the presence of 0.01%SO2 and 6%H2O,the NOx conversions in the presence of Mn-W/TiO2,Mn-Fe/TiO2,or Mn-Mo/TiO2 maintain 98.5%,95.8%and 94.2%, respectively,after 8 h at 120°C at GHSV 12600 h？ 1 .As effective promoters,WO3 and Fe2O3 can increase N2 selectivity and the resistance to SO2 of MnOx/TiO2 significantly.The Fourier transform infrared（FTIR）spectra of NH3 over WO3 show the presence of Lewis acid sites.The results suggest that WO3 is the best promoter of MnOx/TiO2,and Mn-W/TiO2 is one of the most active catalysts for the low temperature selective catalytic reduction of NO with NH3.

Study on the active sites of Cu-ZSM-5 in trichloroethylene catalytic combustion with air

The catalytic activity of Cu-ZSM-5 in trichloroethylene （TCE） combustion increases with the increasing skeletal Cu amount and however decreases with the increase of surface amorphous CuO, which is detected by infrared spectroscopy （IR） and diffuse reflectance ultraviolet-visible spectroscopy （DRS-UV-vis）, therefore the skeletal Cu species are concluded to be the active sites for the TCE combustion.

Catalytic Combustion of Methane over Ti-Pillared Clay Supported Copper Catalysts

A natural montmorillonite, produced from Laiyang of Shandong Province, was pillared by Tipolyeations to form Ti-pillared clay (Ti-PILC), and characterized by BET surface area, infrared spectra and thermal analysis. The characterization results show that Ti-PILC has a larger surface area and more hydroxyl groups than that of the natural clay, thus was used as the catalytic carriers to prepare supported Cu catalysts (Cu/Ti-PILC). The 20%Cu/Ti-PILC with 10mmol/g of Ti/clay shows a high catalytic performance of methane combustion in the temperature range of 400 500℃.

Catalytic combustion study of soot on Ce_(0.7)Zr_(0.3)O_2 solid solution

The Ce0.7Zr0.3O2 solid solution and CeO2 were prepared using the sol-gel method. The phase structure, crystallite sizes and the reducibility of the catalysts were characterized by XRD and H2-TPR techniques. XRD results indicated that Zr^4＋ had replaced part of Ce^4＋ to form a fluorite-like solid solution, which was favorable to obtain ultrafine nanoparticles. The ratio of main HE consumption for Ce0.7Zr0.3O2：CeO2 was 4.4：1.0, implying that the solid solution could improve the reducibility compared to the single CeO2. The Ce0.7Zr0.3O2 solid solution catalyst showed a sharp combustion peak at 397 ℃, which was 200 ℃ lower than that of the single soot. The good catalytic activity of the Ce0.7Zr0.3O2 was attributed to the formation of nano-CeO2-based solid solution, which enhanced the reducibility and then improved the combustion activity. As Ce0.7Zr0.3O2 could be easily reduced to Ce0.7Zr0.3O2-x meanwhile, after oxygenation, the Ce0.7Zr0.3O2.x was recovered to Ce0.7Zr0.3O2 completely. A catalytic combustion reaction mechanism was proposed： the Ce0.7Zr0.3O2 was reduced to Ce0.7Zr0.3O2-x by the reaction with carbon and then it was recovered to Ce0.7Zr0.3O2-x by the interaction with O2.

Catalytic Combustion of Methane over MnO_x/ZrO_2-Al_2O_3 Catalysts

MnO_x/Al_2O_3 and MnO_x/ZrO_2-Al_2O_3 catalysts were prepared by incipientwetness impregnation of Mn(CH_3COO)_2 on the corresponding supports, followed by thecharacterization using X-ray diffraction (XRD), temperature programmed reduction (TPR) and BETsurface area techniques. The result shows the BET surface area of ZrO_2-Al_2O_3 is lower than thatof Al_2O_3 due to the loading of ZrO_2. However the resulted MnO_x/ZrO_2-Al_2O_3 catalyst exhibitshigher activity for methane combustion than MnO_x/Al_2O_3, because the addition of ZrO_2 ontoAl_2O_3 is beneficial for the dispersion of Mn species and the improvement of the lattice oxygenactivity in MnO_x, subsequently the activation of methane during combustion. The optimum loading ofZr in MnO_x/ZrO_2-Al_2O_3 is in the range of 5%-10% correlated with the calcination temperatures ofcatalyst supports.

Catalytic combustion of ethyl acetate over CeMnO_x and CeMnZrO_x compounds synthesized by coprecipitation method

Ce0.6Mn0.4O2 catalysts with different sources of manganese and Ce0.6-xZrxMn0.4O2 mixed oxide catalysts were prepared by coprecipitation method and were characterized by N2 adsorption-desorption,TPR,XRD,and XPS techniques.The activities of the prepared catalysts for ethyl acetate combustion,and the effects of calcination temperature and space velocity on catalytic activity were investigated.The results showed that partial replacement of Mn（NO3）2 with KMnO4 as sources of manganese could improve activities of catalysts.Ce0.45Zr0.15Mn0.4O2 catalyst exhibited the best catalytic activity and high thermal stability,e.g.,T90 could be still below 210℃ even if space velocity was up to 20000h-1.

Catalytic Combustion of Diesel Soot over K_2NiF_4-type Oxides La_(2-x)K_xCuO_4

The K2NiF4 type oxides, La2-x KxCuO4 complex oxides with nanometric size were prepared by sol-gel method. The characters of these samples were analyzed by H2-TPR, XRD, FT-IR and SEM. The catalytic activity for soot combustion was evaluated by temperature-programmed reaction （TPO） technique. The results demonstrate that the substitution of K^＋ for La^3＋ at A-site will increase the catalytic activities of La2-xKxCuO4 to soot combustion greatly, and the substitution quantity affects the structure and catalytic activity obviously. The La1.8 K0.2 CuO4 complex oxides with tetrahedral structure has the best catalytic activity for soot removal reaction, the ignition temperature of soot combustion is decreased from 490 to 320℃.

Characterization of Pr-CeO_2 Nano-crystallites Prepared by Low-temperature Combustion&Hydrothermal Synthesis

Pr-CeO2 Nano-crystalline red pigments were prepared by low-temperature combustion with a later hydrothermal treatment using Ce（NO3）3·6H2O and Pr6O11 as raw materials. The phase composition, coloring mechanism and morphology of pigments were analyzed by XRD, SEM, EDS and XPS. Results showed that Pr-CeO2 solid solution with a fluorite structure was obtained by the diffusion of Pr^＋3 into CeO2 crystal lattice during the synthesis process. XPS analysis indicated that Pr^＋3 substitutes Ce^＋4 in CeO2 and is compensated by oxygen vacancies. Compared with low-temperature combustion synthesis, the Pr-CeO2 pigments prepared with a subsequent hydrothermal treatment have an average grain size of about 16.70 nm, and the crystallinity and red tonality are improved.