Ce-modified AlZr pillared clays supported-transition metals for catalytic combustion of chlorobenzene

In this article, we provided a one-step hydrothermal method to prepare composite AlZr pillaring agents, and synthesized AlZr-pillared clays (AlZr-PILC) via ion exchange. Compared with conventional methods, our method successfully shortened synthetic routes and greatly reduced consumption of the materials. Then, AlZr-PILC-supported manganese and cerium oxide catalysts were obtained by impregnation method. The compositions and properties of these catalysts were characterized by some technical means. The energy dispersive X-ray spectroscopy clearly shows the existence of Mn, Ce, and O, which indicates the successful loading of the active components on the surface of AlZr-PILC. Meanwhile, the results of X-ray diffraction (XRD) and N₂ adsorption experiments demonstrate that the synthesized AlZr-PILC outperforms the raw clays (Na-mmt) and mononuclear Al-PILC in the catalytic combustion of chlorobenzene. XRD and high-resolution transmission electron microscopy also proves that the high activity of them is related to the high dispersion of the oxides and the exposure of more active sites. H₂-temperature-programmed reduction shows that cerium can promote the redox cycles of the manganese system through the strong interactions between MnO₂, CeO₂ and AlZr-PILC. In particular, MnCe(9:1)/AlZr-PILC shows the best catalytic activity in the catalytic combustion of chlorobenzene.     

MCM-41 supported nano-sized CuO-CeO_2 for catalytic combustion of chlorobenzene

In this paper,MCM-41 was synthesized by a soft template technique and MCM-41 supported CuO-CeO_2 nano-sized catalysts with different Cu/Ce molar ratios were prepared by a deposition-precipitation method.N_2 adsorption,HRTEM-EDS,H_2-TPR,XPS characterization,as well as catalytic activity and durability tests for the catalytic combustion of chlorobenzene(CB) were conducted to explore the relationship between the structure and catalytic performance of the catalysts.It is revealed that cuCe(6:1)/MCM-41 has the highest activity and can completely catalyze the degradation of CB at 260℃.The reasons for the high activity of the catalysts are as follows:MCM-41,a type of mesoporous material which has large pore size and large specific surface area,is suitable as a catalyst carrier.The average diameter of nano-sized CuO and CeO_2 particles is about 3-5 nm and adding CeO_2 improves the dispersion of active component CuO,which are highly and evenly dispersed on the surface of MCM-41.Characterization results also explain why MCM-41 supported CuO-CeO_2 with appropriate proportion can highly enhance the catalytic activity.The reason is that CeO_2 acting as an oxygen-rich material can improve the mobility of oxygen species through continuous redox between Ce~(4+)and Ce~(3+),and improve the catalytic performance of CuO for CB combustion.Besides,CuCe(6:1)/MCM-41 also displays good durability for CB combustion,both in the humid condition and in the presence of benzene,making it a promising catalytic material for the elimination of chlorinated VOCs.     

Synergetic catalytic removal of chlorobenzene and NOx from waste incineration exhaust over MnNb0.4Ce0.2Ox catalysts: Performance and mechanism study

Nb doped MnCe_0.2O_x complex oxides catalysts prepared via a homogeneous precipitation method were investigated for synergistic catalytic removal of NO_x and chlorobenzene (CB) at low temperatures. The MnNb_0.4Ce_0.2O_x catalyst with a molar ratio of Nb/Mn = 0.4 exhibits excellent activity and the NO_x and CB removal efficiency reaches 94.5% and 96% at 220 °C, respectively. Furthermore, the NO_x and CB removal efficiency of MnNb_0.4Ce_0.2O_x still remains above 80% after injecting 300 ppm SO₂ and 7 vol% H₂O for 36 h. In addition, the presence of CB and NO_x + NH₃ can improve the NO_x and CB removal efficiency of MnNb_0.4Ce_0.2O_x, respectively. The analysis results from N₂-BET, Py-IR, H₂-TPR and NH₃-TPD reveal that the introduction of Nb increases the average pore size, pore volume and surface area, promoted the growth of Lewis acid amount obviously, and enhances redox ability of MnCe_0.2O_x at 100–250 °C. Moreover, the molecular migration process of NO_x, NH₃, CB and SO₂ in NH₃-SCR and CB oxidation reaction over MnNb_0.4Ce_0.2O_x catalysts were systematically studied. In situ DRIFTS, FT-IR and XPS also confirm that the adsorption of sulfate species and SO₂ on the surface of MnNb_0.4Ce_0.2O_x is inhibited effectively by the introduction of Nb in the presence of SO₂ and H₂O. Moreover, Nb additives also enhance the structural stability of MnNb_0.4Ce_0.2O_x, due to the interactions among Mn, Nb and Ce. The NH₃-TPD, H₂-TPR and in situ DRIFTS results also confirm that the MnNb_0.4Ce_0.2O_x still retains abundant acid sites and high redox ability in the presence of SO₂ and H₂O. In summary, MnNb_0.4Ce_0.2O_x catalysts represent a promising and effective candidate for controlling NO_x and CB at low temperatures.     

Low temperature catalytic oxidation of NO over different-shaped CeO2

To investigate the effect of CeO₂ nanomaterial morphology on its performance for NO catalytic oxidation. Three kinds of CeO₂ nanomaterials including CeO₂ nanorods, nanospheres and nanoparticles were prepared by hydrothermal method and used for catalytic oxidation of NO at low temperature. The experimental results show that CeO₂ nanorods are of the best catalytic performance. Characterization techniques including TEM, XRD, H₂-TPR, NO-TPD and XPS were used to determine the relationship between the morphology of CeO₂ nanomaterial and its catalytic performance. TEM images show that CeO₂ nanorods predominantly exposed (110) and (1 0 0) planes, while CeO₂ nanospheres and CeO₂ nanoparticles predominantly exposed (1 1 1) plane. The excellent catalytic performance of CeO₂ nanorods could be ascribed to the low crystallinity, high reducibility, strong NO adsorption ability and the presence of more surface chemisorbed oxygen.     

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.     

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.     

Understanding the role of tungsten on Pt/CeO2 for vinyl chloride catalytic combustion

Spherical CeO₂ synthesized by the hydrothermal process was used as support to prepare Pt/WO₃/CeO₂,and the effects of tungsten(W) contents on activity,stability and polychlorinated by-products were investigated to understand the role of W for vinyl chloride(VC) catalytic oxidation.The introduction of12 wt% W to Pt/CeO₂(P12 WC) exhibits the highest catalytic activity with 90% conversion of VC at 250℃,meanwhile the stability improves and the polychlorinat...     

Core-shell MnCeOx catalysts for NO oxidation and mild temperature diesel soot combustion

Environmental contamination such as soot particles and NO_x has aroused extensive attraction recently.However,the main challenge lies in the oxidation of soot at mild temperature with the assistance of NO_x.Here,a series of core-shell MnCeO_x catalysts were successfully synthesized by hydrothermal method and employed for low-temperature catalytic oxidation of soot in the presence of NO_x.X-ray diffraction(XRD),inductively coupled plasma-optical emission sp...     

High activity of CeO_2-TiO_2 composites for deep oxidation of 1,2-dichloroethane

CeO_2-TiO_2 catalysts prepared by different methods were investigated for deep oxidation of 1,2-dichloroethane(DCE),as a typical representative of the chlorinated volatile organic compounds(CVOCs).Characterization analysis reveals that CeO_2-TiO_2 catalysts prepared by sol-gel and coprecipitation methods exhibit higher specific area,CeO_2 and TiO_2 particles are highly dispersed into each other and the reducibility and mobility of active oxygen species are obviously promoted due to the strong interaction between the two catalysts CeO_2 and TiO_2,resulting in higher catalytic activity for DCE oxidation to and less chlorinated byproduct.The high calcination temperature would lead to the formation of a new monoclinic phase Ce_(0.3)Ti_(0.7)O_2 and sintering,which is the main reason for the catalytic activity for DCE oxidation markedly decreases.     

Acid modified carrier on catalytic oxidation of dichloromethane over CeO2/HZSM-5 catalysts

In this study, a series of Hydrogen-Zeolite Socony Mobil-5-X (HZSM-5-X) catalysts were prepared by acid modification, then Ce/HZSM-5-X (X = 0, 0.2, 0.4, 1.0, 2.0) catalysts were prepared by impregnation method. The catalytic performance of the catalysts on dichloromethane (DCM) oxidation was investigated. Through different characterizations, HZSM-5-X exhibit high specific surface area, good redox ability, rich acidity and much suitable acidic site distribution after acid treatment. Among them, Ce/HZSM-5-0.4 shows better catalytic activity with the lowest by-product and the best CO₂ yield. Its T₉₀ is 302 °C and the CO₂ yield of T₉₀ is more than 80 wt%, which demonstrates that the acid modification of carrier plays the positive effect on the catalytic capacity for DCM oxidation.     

A mechanic insight into low-temperature catalytic combustion toward ethylene oxide over Pt-Ru/CuCeOx bimetallic catalyst

The catalytic oxidation performance toward ethylene oxide(EO) and the consequent mechanism were investigated on the Pt-Ru/CuCeO_x bimetallic catalyst,which was prepared by a distinct method combining stepwise adsorption and subsequent impregnation.The catalytic tests show that the introduction of Ru into the Pt catalyst,so as to form Pt-Ru bimetallic active sites,can greatly increase the oxidation activity of the catalyst,as evidenced by the extremely lower full oxidation temperature(1...     

Effect of Na~+ on catalytic performance of CoCe/ZSM-5 catalysts for oxidation of toluene

A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene.To study the effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts,a series of different Si/Al ZSM-5 zeolites and catalysts doped with Na were synthesized.The experimental results show that 0.71 wt%Na+can inhibit active growth,generate more active small crystal grains,and promote improvement of the catalytic activity by the grain boundary segregation block mechanism,and the catalyst with 0.71 wt%of Na shows toluene conversion of 90 vol%at 250℃.Over 0.71 wt%of Na+content will neutralize the acid centre of the catalyst,lowering the specific surface area of the catalyst and resulting in a gradual decrease in the catalytic activity.     

Storage-reduction strategy for NOx reduction from gas turbine exhaust with W-Ti-CeOx catalyst in natural gas power plants

Traditional vanadium-based selective catalytic reduction(SCR) deNO_x catalyst can hardly adapt to the gas conditions(much high NO2/NO_x ratio at lower temperature) of the start-up and low loading periods for a gas turbine.Therefore,a W-Ti-CeO_x catalyst with NO_x storage and reduction(NSR)function was developed in this work for gas turbine exhaust NO_x elimination.The experimental results reveal that W-Ti-CeO_x catalyst exhibits high NO...     

Application of MnCeOx supported on palygorskite and Al(OH)3 for HCHO oxidation: Catalytic performance and stability

Indoor formaldehyde (HCHO) is an important air pollutant, while it is very difficult to reduce HCHO to low-level (e.g. <0.08 mg/m³). Catalytic oxidation at ambient temperature has been increasingly recognized as one of the important methods to mitigate HCHO pollution due to its good effectiveness, stability, and recyclability. To further improve the activity of catalytic oxidation, this study develops the integrated MnCeO_x catalysts supported on palygorskite (Pal) and aluminium hydroxide (Al(OH)₃). Our results indicate that the synergistic interaction in MnCeO_x through the oxygen transfer mechanism from the oxygen reservoir CeO₂ to MnO_x significantly improves the activity. Pal, Al(OH)₃, etc. were applied as the supports with a focus on their dispersion, microstructure, strength, and relative role. MnCeO_x can be anchored on the surface of Al(OH)₃ with high dispersion. With the integrated catalyst, HCHO concentration decreases from 1.012 to 0.086 mg/m³ within 48 h. Higher oxidation activity of MnCeO_x powder may be ascribed to the amount of active components on the surface. The incorporation of ZSM–5 and activated carbon can improve the adsorption of HCHO, and all integrated catalysts exhibit stronger activities, with HCHO being degraded to the level lower than 0.08 mg/m³. Meantime, the samples exhibit good stability and strength (20.2 MPa) without obvious decrease over five consecutive stability experiments.     

Controllable synthesis of argentum decorated CuOx@CeO2 catalyst and its highly efficient performance for soot oxidation

In this paper, CuO_x@Ag/CeO₂ catalysts were synthesized by simple wet-chemical method and equal volume impregnation method. The obtained catalysts were subjected to soot temperature programmed oxidation (soot-TPO) activity tests and were further characterized by various techniques such as X-ray diffraction (XRD), transmission electron microscopy/high-resolution transmission electron microscopy (TEM/HR-TEM), N₂ physisorption, X-ray photoelectron spectroscopy (XPS) and H₂-temperature programmed reduction (H₂-TPR). The results show that CuO_x@Ag/CeO₂ synthesized presents well controlled core-shell structures, with nano-cube like Cu₂O as the core and Ag decorated polycrystalline CeO₂ grafting layers as the shell. Such core-shell structured CuO_x@Ag/CeO₂ can successfully construct a secondary oxygen delivery channel (CuO_x → CeO₂ → Ag) to effectively transfer bulk oxygen of the catalyst to the soot, resulting in its excellent soot oxidation activity compared to CuO_x@CeO₂. The potential benefiting effect by Ag introduction over Cu@Ag/Ce can be concluded as: (i) pumping lattice oxygen and accelerating gaseous O₂ dissociation to generate significantly increased active surface oxygen content; (ii) modulating a moderate surface oxygen vacancies concentration to maintain more highly active O₂^– species.     

Mesoporous CeO_2-C hybrid spheres as efficient support for platinum nanoparticles towards methanol electrocatalytic oxidation

The development of direct methanol fuel cells(DMFCs) is partially limited by the poor kinetics of methanol oxidation reaction(MOR) at the anode side.It was reported that the interaction between Pt and CeO_2 enhances the electrocatalytic performance of Pt catalyst for MOR.In this work,a hybrid material(CeO_2-C) composed of CeO_2 and carbon was successfully prepared by a simple hydrothermal method followed by calcination in inert atmosphere.The hierarchically porous nanostructure and especially good electronic conductivity of CeO_2-C make it an excellent support for Pt particles for application in electrocatalytic process.TEM investigation reveals that triple-phase interface of Pt,carbon and CeO_2 forms in Pt/CeO_2-C catalyst.Performance of the as-prepared catalyst for MOR was studied in alkaline medium.The Pt/CeO_2-C catalyst shows superior catalytic performance for MOR compared with Pt/CeO_2 and the physical mixture of Pt/CeO_2 and acetylene black(Pt/CeO_2+C).The significantly improved performance can be attributed to the synergetic effect between Pt particles and CeO_2-C support,and the better conductivity of CeO_2-C.This study provides a possible method to expand the application potential of CeO_2 materials in MOR,and may also be used in other electrocatalytic process.     

Active manganese oxide on MnOx–CeO2 catalysts for low-temperature NO oxidation: Characterization and kinetics study

MnO_x–CeO₂ catalysts were synthesized to investigate the active sites for NO oxidation by varying the calcination temperature. XRD and TEM results showed that cubic CeO₂ and amorphous MnO_x existed in MnO_x–CeO₂ catalysts. High temperature calcination caused the sintering of amorphous MnO_x and transforming to bulk crystalline Mn₂O₃. H₂-TPR and XPS results suggested the valence of Mn in MnO_x–CeO₂ was higher than pure MnO_x, and decreased with the increasing calcination temperature. The turnover frequency (TOF) was calculated based on the initial reducibility according to H₂-TPR quantitation and kinetic study. The TOF results indicated that the initial reducibility of amorphous MnO_x with high valence manganese ions was equivalent to the active sites for NO oxidation. It can be inferred that the amorphous MnO_x plays a key role in low-temperature NO oxidation.     

Fabricating PdCe/OMS-2 catalysts with boosted low-temperature activity for toluene deep degradation

Porous cryptomelane-type octahedral molecular sieve(OMS-2) with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds(VOC) catalytic elimination.However,complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability.Here,a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the p...     

Catalytic performance of Zr-doped CuO-CeO_2 oxides for CO selective oxidation in H_2-rich stream

Zr-doped CuO-CeO_2 catalysts for CO selective oxidation were designed and prepared by the hydrothermal method and coprecipitation. The experimental samples were characterized by means of N_2 adsorption-desorption isotherms, powder X-ray diffraction, temperature-programmed reduction and Xray photoelectron spectroscopy. It is observed that the catalyst prepared by hydrothermal method exhibits larger specific surface area, smaller crystalline size and higher dispersion of active components compared with those of the catalyst obtained by coprecipitation. Meanwhile, redox properties of copper oxide are improved significantly and highly dispersed copper species providing CO oxidation sites are present on the surface. Furthermore, adsorptive centers of CO and active oxygen species increase on the copper-ceria interfaces. The Zr-doped CuO-CeO_2 catalyst prepared by hydrothermal method possesses superior catalytic activity and selectivity for selective oxidation of CO at low temperature compared with those of the sample prepared by coprecipitation. The temperature corresponding to 50% CO conversion is only 73 ℃ and the temperature span of total CO conversion is expanded from 120 to 160 ℃.     

FeCe nanocomposite with high iron content as efficient catalyst for generation of CO_x-free hydrogen via ammonia decomposition

FeCe nanocomposite catalysts with different iron contents were synthesized by a facile co-precipitation method.The as-prepared materials were characterized by various techniques including powder X-ray diffraction(XRD),N_2 adsorption/desorption and high-resolution transmission electron microscopy(HRTEM).Catalyst with the highest iron content(90 FeCe) shows the best activity for the hydrogen generation via ammonia decomposition.83% NH_3 conversion is achieved at 550℃ and nearly full conversion of NH_3 is realized at 600℃ with a GHSV of 24000 cm~3/(g_(cat)·h).The large content and small size crystal particles of iron species are responsible for the good catalytic performance.Temperatureprogrammed reduction by hydrogen(H_2-TPR) was performed to investigate the interaction between cerium and iron species.It is found that slight cerium can exert strong interaction with iron compound thus effectively prevent the self-aggregation of active iron species,so as to improve the catalytic activity for ammonia decomposition.