Effect of tourmaline additive on the crystal growth and activity of LaCoO3 for catalytic combustion of methane

LaCoO3/tourmaline was prepared as catalysts on the methane catalytic combustion. As additive tourmaline, its effect on crystal growth and catalytic activity of LaCoO3, were investigated via X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), H2-temperature programmed reduction(H2-TPR) and catalyst evaluation techniques. SEM and TEM indicated that the spontaneous polarizability of tourmaline made LaCoO3 particles grow dispersedly on tourmaline, alleviated the agglomeration and exposed more reactive sites. It was a main influence leading to the improvement of catalysts activity, exposed via catalyst evaluation device. Among the different additive proportion of compound samples, the 2% tourmaline added LaCoO3 showed an obvious enhancement activity compared to non-tourmaline sample—the light-off temperature was 454 °C and CH4 reached the full conversion at 563 °C.     

Synthesis of La_xK_(1–x)CoO_3 nanorod and their catalytic performances for CO oxidation

A series of Lax K1–x CoO3 nanorod oxides with perovskite structure were synthesized by sol-gel method using polyvinyl alcohol(PVA) as additive.These perovskite-type complex oxide catalysts were characterized by the techniques of X-ray diffraction(XRD),infrared(IR),Brumauer-Emmett-Teller(BET) and scanning electron microscopy(SEM).And the results showed that nanorods of La1–x Kx CoO3 perovskite-type complex oxides were fabricated by sol-gel method when the mass concentration of PVA was 4% and the calcined temperature kept at 700 ℃ for 4 h.The catalytic results of CO oxidation showed that the Lax K1–x CoO3 catalysts had high activity.LaCoO3 nanorods exposed more {110} plane than LaCoO3 nanoparticles,which was beneficial to the catalytic oxidation of CO.LaCoO3 nanorods had the best catalytic performance for the oxidation of CO.At 200 oC,the CO conversion could reach 100%.     

Synthesis and catalytic performance of macroporous La_(1-x)Ce_xCoO_3 perovskite oxide catalysts with high oxygen mobility for catalytic combustion of soot

The disordered macroporous-mesoporous La_(1-x)Ce_xCoO_3 catalysts were prepared by complexcombustion method with ethylene glycol as complexing agent at relatively low calcination temperature.The samples were characterized by means of X-ray diffraction,N2 adsorption-ndash;desorption,Xray photoelectron spectroscopy,transmission electron microscopy,hydrogen temperature-programmed reduction and soot temperature-programmed reduction,and so on.The results show that the use of complexing agent and relatively low calcination temperature increase the specific surface area of the catalyst and have abundant pore structure.The Ce ions introduced into lattice of LaCoO_3 mainly exist in the form of tetravalent.At the same time,Ce ions enhance the redox performance of the catalyst and the mobility of active oxygen species,which enhances the catalytic activity of the catalyst for soot combustion.The results of activity test show that La_(0.9)Ce_(0.1)CoO_3 catalyst exhibits the highest activity in the absence of NO and NO_2,and its T_(10),T_(50) and T_(90) are 371,444,and 497℃,respectively.At the same time,a possible reaction mechanism is proposed in this study based on the turnover frequency(TOF) calculated by isothermal anaerobic titrations,XPS and XRD results.     

Comparative study of La_(1-x)Ce_xMnO_(3+δ) perovskites and Mn-Ce mixed oxides for NO catalytic oxidation

A series of La_(1-x)Ce_xMnO_(3+δ)(x=D,0.05,0.1,0.2,and 0.3) perovskites and Mn-Ce mixed oxides were prepared.Their physico-chemical properties were systematically characterized and the NO oxidation activities of the catalysts were investigated.The La_(0.9)Ce_(0.1)MnO_(3+δ) has the best activity among all of the catalysts,with a maximum NO conversion of 85% at 300℃.The characterization results indicate that the doping of Ce improves the properties of the perovsidtes in terms of the specific surface area,the average valence state of Mn ions,the number of reactive oxygen species and the NO_x desorption behaviors.The Mn-Ce mixed oxide calcined at 500℃ shows a similar NO oxidation activity with La_(0.9)Ce_(0.1)MnO_(3+δ).However,the activity of the mixed oxide obtained at 750℃ decreases a lot,which results from the loss of active sites and active oxygen species.     

Effect of calcination temperature on steam reforming activity of Ni-based pyrochlore catalysts

This work served as the second part of a study evaluating the effect of calcination temperature(700-1000℃) on Ni-based lanthanum zirconate pyrochlore catalysts for methane steam reforming.A previous study(Haynes et al.Ceram.Int.2017(43) 16744) provided a thorough characterization of the material properties for the catalysts used here,and this study focuses on the evaluation of catalytic activity.The activity was assessed by two different experimental studies:the effect of reaction temperature using a temperature programmed surface reaction(TPSR),and the effect of reaction pressure.The results demonstrate a complex interaction between the Ni particles and surface LaO_x species under the methane steam reforming conditions.Specifically,the material calcined at the lowest temperature(700℃) possesses the highest activity and selectivity,which is attributed to smaller and more welldispersed Ni particles on the surface,and,more importantly,a lesser degree La enrichment at the surface.All catalysts were deactivated by steam to NiO under all conditions tested,but at certain low reaction pressure(p=0.23 MPa) conditions the materials calcined at 700-900℃ are able to completely recover equilibrium activity in-situ that is then robust and stable under both low and high reaction pressures(p=1.8 MPa) suggesting the formation of a synergistic relationship between Ni and La for syngas production.However,exposure of a fresh material to high reaction pressures leads to a rapid and irreversible loss in both CH4 conversion and syngas selectivity whether in the fresh(no pretreatment),or pretreated(steam,H_2 or Ar only at 800℃) form for any catalyst.The mechanism for deactivation appears to be due to the presence of LaO_x species that become mobile,possibly by the formation of La-OH,and covers the active Ni particles and inhibits sites responsible for the CH4 decomposition.     

In-situ generation of platinum nanoparticles on LaCoO3 matrix for soot oxidation

The LaCo_0.94Pt_0.06O₃ catalyst is reduced under 5% H₂/Ar at different temperatures to get Pt/LaCoO₃ with high catalytic activity for soot oxidation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR), O₂-temperature programmed desorption (O₂-TPD) and thermogravimetric analysis (TGA) were used to study the physicochemical properties of the catalyst. SEM and TEM results indicate that Pt nanoparticles (<10 nm) are grown homogeneously on the surface of the LaCoO₃ matrix after in-situ reduction. XRD shows that the reduced catalyst has a high symmetrical structure. TGA results indicate that all reduced catalysts exhibit an excellent activity, especially the catalyst reduced at 350 °C (T₁₀ = 338 °C, T₅₀ = 393 °C, T₉₀ = 427 °C). And perovskite is the primary active component. According to XPS study, the high symmetrical structure benefits the mobility of oxygen vacancy, and Pt nanoparticles induce the oxygen vacancy to move to its adjacent situation, resulting in more adsorbed oxygen on the surface of the reduced catalyst and increasing the activity. The possible reaction principle is also proposed.     

One-pot synthesis of Cu-Ce co-doped SAPO-5/34 hybrid crystal structure catalysts for NH_3-SCR reaction with SO_2 resistance

SAPO-34,SAPO-5/34 based catalysts doped with Cu,Ce as active components were synthesized via a one-pot hydrothermal method by using different amounts of additive(a-cellulose),and their catalytic activities were measured for selective catalytic reduction(SCR) of NO with NH3.The synthesized Cu-Ce co-doped products switch from cubic SAPO-34,to flower-like aggregated SAPO-5/34,hybrid crystal SAPO-5/34,and finally to spherical aggregated SAPO-34 with the increase of α-cellulose amount.The Cu-Ce co-doped SAPO-5/34 hybrid crystal structure catalysts with 0.75 mol ratios of C/P(Cu-Ce/SP-0.75)exhibit excellent NH3-SCR activity with higher than 90% NO_x conversion in the temperature range of 180-450℃,at WHSV of 20000 mL/(g·h).Furthermore,the catalyst displays outstanding sulfur resistance and NO_X conversion maintains above 90% at 200-450℃ after adding 100 ppm of SO_2.The characteristic results suggest that the high deNO_X performance of Cu-Ce/SP-0.75 is due to the enhanced accessibility,abundant activity species,excellent redox property and high adsorptive and activated capacity for NH3.     

Support interaction of Pt/CeO_2 and Pt/SiC catalysts prepared by nano platinum colloid deposition for CO oxidation

The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO_2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method,and their catalytic performance in CO oxidation was investigated.XRD,TEM,XPS and H_2-TPR were used to identify the states of Pt particles on the support surface,as well as their effect on the performance of the catalysts.Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity.Under the oxidative treatment at low temperature,the Pt-O-Ce interaction plays an important role in improving the catalytic activity.After calcining at high temperature,enhanced Pt-O-Ce interaction results in the absence of metallic Pt~0 on the support surface,as evidenced by the appearance of Pt~(2+) species.It is consistent with the XPS data of Pt/CeO_2,and is the main reason behind the deactivation of the catalyst.By contrast,either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt~0 state on the SiC surface even after aging at 800℃in an oxidizing atmosphere.Thus,the Pt/SiC shows better thermal stability than Pt/CeO_2.The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature,but strong interactions may induce serious deactivation of catalytic activity.     

Catalytic feasibility of Ce-doped LaCoO3 systems for chlorobenzene oxidation: An analysis of synthesis method

A family of Ce-doped LaCoO₃ perovskites are presented as possible catalysts for Cl–VOCs elimination. These materials with different contents of Ce were obtained through the citrate and the reactive grinding methods. The insertion of Ce in the original perovskite structure favours the presence of Co²⁺/Co³⁺ and Ce³⁺/Ce⁴⁺ redox pairs and a higher content of oxygen vacancies that enhances the catalytic performance in chlorobenzene combustion based on differential kinetics studies. The family obtained by the grinding method presents a performance as high as that synthesized by citrate method. Thus, the reactive grinding is a feasible green chemistry alternative to obtain a catalyst with the same performance as that obtained from traditional methods. Finally, the stability of samples was evaluated under total combustion reaction conditions showing an excellent activity during 45 h time on stream.     

Effect of surface manganese oxide species on soot catalytic combustion of Ce–Mn–O catalyst

Constructing cerium and manganese bimetallic catalysts with excellent catalytic performance for soot combustion is the research frontier at present. In order to find out the key factors for catalytic soot combustion of Ce–Mn–O catalysts, a series of Ce–Mn–O catalysts with different Ce/Mn proportions were prepared by co-precipitation method. The activity test results show that it increases first and then decreases with the increase of Mn content. The best catalytic activity is obtained for Ce_0.64Mn_0.36 catalyst, which shows a maximum rate temperature (T_m) at 306 °C for CO₂ production in TPO curve. Compared with non-catalytic soot combustion, the T_m decreases by more than 270 °C. Systematical characterization results suggest that when the adsorbed surface oxygen, lattice oxygen, specific surface area and total reduction amount of the catalysts reach a certain value, the key factors leading to the difference of catalytic activity become the readily reducible and highly dispersed surface manganese oxide species and contact performance of the external surface. The surface manganese oxide species is beneficial to improving the low-temperature reducibility of catalysts and the porous surface is conducive to the contact between catalyst and soot. Furthermore, for the soot combustion reaction containing only O₂, the promoting effect of Mn⁴⁺ is not obvious.     

Ce-Fe-Mn ternary mixed-oxide catalysts for catalytic decomposition of ozone at ambient temperatures

Ce-modified Mn-Fe mixed-oxide catalysts were prepared by a citric acid sol-gel method and characterized by X-ray diffraction,Raman,N_2 adsorption-desorption,infrared spectra H_2 temperature-programmed reduction and thermogravimetric analyses.Their catalytic properties were investigated in ozone(O_3)decomposition reaction.Results show that the small amount of rare earth metal Ce added during Mn-Fe(FM) mixed-oxide synthesis greatly improves the catalytic performance in O_3 decomposition.Among the prepared catalysts.the C_(0.04)(FM)_(0.96) mixed-oxide catalyst exhibits the highest catalytic activity and stability.The O_3 conversion over C_(0.04)(FM)_(0.96) is 98% after 24 h reaction at 25℃ under dry condition,and that over FM decreases to 90% after 16 h reaction.At 0℃,the O_3 conversion over C_(0.04)(FM)_(0.96) is 95% after 7 h reaction under dry condition.and that over FM slows down to 70%.Under humid condition(RH 65%),the O_3 conversion over C_(0.04)(FM)_(0.96) is 63% after 6.5 h reaction at 25℃.while that over FM decreases to 55%.When Ce is doped into Mn-Fe mixed oxides,the small amount of Ce enters the crystal lattice of MnO_2.and partial Fe is separated to form Fe_2O_3.This changes cause lattice distortion and increase defects and enable the as-synthesized Ce-Fe-Mn ternary mixed-oxide catalysts to acquire additional oxygen vacancies and increase their specific surface area,thereby increasing the number of reaction sites and enhancing the catalytic performance of the catalysts forO_3 decomposition.     

Rh/CeO2 composites prepared by combining dealloying with calcination as an efficient catalyst for CO oxidation and CH4 combustion

In this paper, a series of Rh/CeO₂ catalysts with three-dimensional porous nanorod frameworks and large specific surface area were prepared by chemical dealloying Al–Ce–Rh precursor alloys and then calcining in pure O₂. The effects of the Rh content and calcination temperature on CO oxidation and CH₄ combustion were studied, and the results reveal that the Rh/CeO₂ catalysts produced by dealloying melt-spun Al_91.3Ce₈Rh_0.7 alloy ribbons and then calcining at 500 °C exhibit the best catalytic activity, the reaction temperatures for the complete conversion of CO and CH₄ are as low as 90 and 400 °C, respectively. Furthermore, after 150 h of continuous testing at high concentrations of H₂O and CO₂, the nature of the catalyst is not irreversibly destroyed and can still return to its initial level of activity. This excellent catalytic activity is attributed to a portion of Rh being uniformly distributed on the CeO₂ nanorod surface in the form of nanoparticles, forming strong Rh–CeO₂ interfacial synergy. Another portion of Rh permeated into the CeO₂ lattice, which results in a significant increase in the number of oxygen vacancies in CeO₂, thus allowing more surface active oxygen to be adsorbed and converted from the gas phase. Moreover, the catalytic reaction can proceed even in an oxygen-free environment due to the excellent oxygen storage performance of the Rh/CeO₂ catalyst.     

Fabrication of La_(1-x)Ca_xFeO_3 perovskite-type oxides with macro-mesoporous structure via a dual-template method for highly efficient soot combustion

A series of three-dimensionally ordered macro-mesoporous(3DOMM) La_(1-x)Ca_xFeO_3(x=0-0.3)perovskite-type oxides were designed and successfully fabricated for the first time via a dual-template method.In which,PMMA and Brij-56 were employed as the hard template and soft template,respectively.It is found that 3 DOMM La_(1-x)Ca_xFeO_3 exhibits abundant wormlike mesoporous channels about 3 nm in diameter on macroporous skeleton walls.The excellent catalytic activity of soot combustion benefits from not only the well-designed hierarchical porous structure of catalyst,but also the redox electron pair of Fe~(3+)/Fe~(4+) induced by the doping of low-valent alkaline earth metal Ca to A-site of LaFeO_3.3DOMM La_(0.8)Ca_(0.2)FeO_3 exhibits superior catalytic performance for soot combustion,which shows T_(50) of396℃.It is 189℃lower than that without catalyst.A combination of structure and composition in the design of catalyst can be widely extended to other catalytic systems.     

Catalytic decomposition of ethyl acetate over La-modified Cu-Mn oxide supported on honeycomb ceramic

The La-modified Cu-Mn spinel oxide was successfully coated onto honeycomb ceramic by a washcoating method for complete catalytic decomposition of ethyl acetate.The La-modified Cu-Mn oxides were characterized by X-ray diffraction,X-ray fluorescence,H_2-temperature programmed reduction,Brunauer-Emmett-Teller method,field-emission scanning electron microscopy and high-resolution transmission electron microscopy.The effects of different precipitants and rare earth doping on the structure and catalytic performance of the catalysts were investigated.The results show that the CuMn_2 O_4 spinel with(NH_4)_2 CO_3 as a precipitant can form a larger specific surface area and a suitable pore size,which is beneficial to the absorption of ethyl acetate.Although the rare earth doping does not significantly change the crystal phase structure of the catalyst,it improves its reducibility and lowers the temperature of the catalytic decomposition.With respect to the catalytic decomposition of ethyl acetate,the rare earth-modified Cu-Mn oxide supported on honeycomb ceramic shows excellent catalytic performance with 100% conversion under the conditions of 239℃,space velocity of 12500 h~(-1) and1000 ppm.And the ethyl acetate removal rate is still 100% after 1440 min of continuous reaction.     

Cerium and ruthenium co-doped La_(0.7)Sr_(0.3)FeO_(3-δ) as a high-efficiency electrode for symmetrical solid oxide fuel cell

Symmetrical solid oxide fuel cells(SSOFCs) could be alternative energy conversion devices due to their simple fabrication process and low cost.Herein,perovskite La_(0.6)Ce_(0.1)Sr_(0.3)Fe_(0.95)Ru_(0.05)O_(3-δ)(LCSFR) was synthesized and evaluated as a high-performance electrode for SSOFCs based on the electrolyte of La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3-δ)(LSGM).LCSFR retains their stable perovskite crystal structure in both reducing and oxidizing atmospheres,though a minor amount of LaSrFeO_4 phase is present under reducing conditions.Morphology investigation shows that homogeneously dispersed Ru metallic nanoparticles are exsolved on the surface of LCSFR after being reduced.The polarization resistance(R_p) of LCSFR-CGO(Ce_(0.9)Gd_(0.1)O_(2-δ)) is about 0.11 Ω·cm~2 at 800℃ in air,while the value of R_p for LCSFR-CGO in wet H_2(3% H_2 O) increases up to 0.32 Ω·cm~2.The symmetrical LCSFR-CGOILSGMILCSFR-CGO cell demonstrates a performance with an open circuit potential(OCV) of 1.07 V and a maximum peak power density of 904 mW/cm~2 at 800℃ using wet H_2 as the fuel.This high performance indicates that LCSFR is a candidate electrode for SSOFCs.     

Sm-MnOx catalysts for low-temperature selective catalytic reduction of NOx with NH3: Effect of precipitation agent

A series of Sm–Mn mixed oxide catalysts were prepared via precipitation using various precipitants, namely Na₂CO₃ (NH₄)₂CO₃, and NH₃·H₂O, and evaluated for the selective catalytic reduction (SCR) of NO_x with NH₃ at low temperatures. Various characterisation techniques were used to determine the physicochemical properties of the catalysts, and it is found that their catalytic performance is greatly influenced by the nature of the precipitation agent used. It is found that Sm_0.1Mn–Na₂CO₃ and Sm_0.1Mn-(NH₄)₂CO₃ exhibit superior catalytic performance in the SCR reaction to that of Sm_0.1Mn–NH₃·H₂O due to an abundance of surface acid sites, high surface concentration of Mn⁴⁺, and high NO oxidation capacity. From in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) analysis, we conclude that the Sm–Mn catalysts follow both Eley-Rideal and Langmuir–Hinshelwood mechanisms, and that the Eley-Rideal mechanism is dominant at elevated temperatures.     

Er-modified MnOx for selective catalytic reduction of NOx with NH3 at low temperature: Promoting effect of erbium on catalytic performance

Various Er modified MnO_x catalysts were synthesized using co-precipitation approach and tested in the selective catalytic reduction of NO_x by ammonia(NH₃-SCR).Catalysts were analyzed with various characterization techniques,and it is found that the doping of Er can enormously enhance the catalytic performance of MnOx catalyst.MnEr_0.1 demonstrates advantageous catalytic performance in the NH₃-SCR reaction owing to rich surface acidic sites,hi...     

Role of cerium dopants in MoVNbO multi-metal oxide catalysts for selective oxidation of ethane

The effect of Ce on the structure of MoVNbCeO multi-metal oxide catalysts and the performance of ethane selective oxidation was investigated. These multi-metal oxide catalysts with superior oxidizability exhibit high catalytic activity, and vanadium acts as the active center for ethane oxidation reaction. The improved catalytic activity is related to the increased V⁵⁺ content on the catalyst surface, which results from the enhanced transformation of the electrons between V and Ce. Moreover, Ce effectively promotes oxygen adsorption, activation, and mobility. And the presence of Ce can also prevent MoO₃ formation and stabilize the Mo₅O₁₄-like structure. In addition, the catalyst with a moderate amount of Ce exhibits outstanding catalytic performance. Especially, the MVN-Ce catalyst with a Ce/V ratio of 0.1 exhibits the best performance: the total selectivity of the catalyst toward C₂H₄ and CH₃COOH is the highest (72%) at the ethane conversion of 31%. Therefore, MoVNbCeO multi-metal oxides are promising candidates for selective oxidation.     

Selective catalytic reduction of NO by NH_3 on cerium modified faujasite zeolite prepared from aluminum scraps and industrial metasilicate

This work was devoted to the study of the selective catalytic reduction of NO by NH_3 on calcined and hydrothermal treated cerium loaded zeolite catalysts.The parent faujasite zeolite Na-F(Si/Al=1.32 and S_(BET)=749 m~2/g) used as support for the preparation of the catalysts was obtained from industrial sodium metasilicate and aluminum scraps.As expected,the NO conversion increases with increasing the percentage of cerium in the structure of the faujasite zeolite.Total NO conversion into N_2 is reached at 400℃at a space velocity of 250 000 h~(-1).The high conversion is due to the redox shift between Ce~(3+)/Ce~(4+)and the strong acid sites related to the rare earth present in the framework that is the key in SCR of NO process.Moreover,the highest loaded cerium catalyst retains almost its activity after hydrothermal treatment at 850℃.This higher loading is desirable for both activity and stability provided that two stages of preparation are used to put the Ce ions in the sodalite cages.     

Effect of different supports on activity of Mn–Ce binary oxides catalysts for toluene combustion

The effects of support materials on catalytic performance were investigated in catalytic removal of toluene. And the Mn–Ce binary oxides as active components were supported on ZrO₂, SiO₂, γ-Al₂O₃ and TiO₂ support materials. Many techniques, including X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and NH₃-temperature-programmed desorption (NH₃-TPD), were used to characterize physicochemical properties. Among the different catalysts, the MnCe/ZrO₂ catalyst with the lowest specific surface area (39.7 m²/g) shows the best catalytic activity. In terms of toluene conversion, the activity order is as follows: MnCe/ZrO₂ > MnCe/TiO₂ ≈ MnCe/SiO₂ > MnCe/Al₂O₃. The better performance of MnCe/ZrO₂ should be attributed to the low-temperature reducibility, and abundant surface species (Mn⁴⁺ and lattice oxygen). And XPS and TPR results reveal that more surface abundant Mn and Ce elements generate good interaction in MnCe/ZrO₂. The weak interaction between metal oxide and support also boosts the dispersion and complete reduction of MnCe oxides at low temperature. In addition, the in-situ DRIFTS results clarify that the carbonate species are main intermediates in MnCe/ZrO₂ sample during surface reaction process.