Revealing active species of CePO4 catalyst for selective catalytic reduction of NOx with NH3

Revealing the active species of the catalyst is conducive to the design of more efficient catalyst.Herein,we tried to demonstrate the roles of amorphous and crystalline structures on CePO₄ catalyst during selective catalytic reduction(SCR) of NO_x by NH₃.Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO₄.Both amorphous and crystalline CePO₄ species on CePO-X samples can...     

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.     

Effects of supports and combined process on hydrogen purification over nickel supported catalysts

Hydrogen purification must be done to meet the different purposes of hydrogen utilization.In the present work,it is confirmed that the catalyst Ni/CeO_2 has the highest activity for total methanation(Total MET) of CO and CO_2,and is thus most suitable for hydrogen purification for ammonia synthesis.While,the catalyst Ni/ZrO_2 appears the best one for selective methanation of CO(CO-SMET) in the H_2-rich gas to produce clean fuel for proton exchange membrane fuel cell(PEMFC).In spite of this,the catalyst Ni/ZrO_2 without adding chlorine ions as promoter is not yet capable of removing the CO in the reformate gas to below 10 ppm in a wide reaction temperature range by the way of CO-SMET.Adding chlorine ions as promoter is indeed not favorable for practical application due to its gradual loss in the catalytic reaction as proved in our previous work.Therefore,a step to decrease CO_2 concentration(called as de-CO_2 step) is suggested to be set prior to the CO-SMET step in this work.It is proved that such combination of de-CO_2 step and CO-SMET step is efficient to achieve a deep removal of CO to below 10 ppm with a high selectivity more than 50% in a wide reaction temperature range of 220—280℃over the catalyst Ni/ZrO_2 without adding chlorine ions as promoter.The combined process has potential for practical application,at least in the large-scale power plant of PEMFC.     

Influence of calcination temperature for LaTi_(0.2)Fe_(0.8)O_3 on catalytic pyrolysis of bagasse lignin

LaTi_(0.2)Fe_(0.8)O_3(LTF)was prepared by the sol-gel method,and the effects of calcination temperature on the structure and properties were investigated,A new method of preparing aryl oxygen-containing compounds from bagasse lignin(BL)by the catalytic pyrolysis over LTF was proposed.The results show that LTF has cubic crystal phase and porous structure and its optimal calcination temperature is 800 ℃(LTF-800).In the test for catalytic pyrolysis of BL,with the addition of LTF-800,the yield of liquid product reaches the maximum; the contents of phenolics,guaiacols,syringols,phenylates and furans increase obviously,while those of benzenes,esters and carboxylic acid decrease.The total content of aryl oxygencompounds(including phenolics,guaiacols,syringols and phenylates)in liquid product is more than 74 wt%with the addition of LTF-800,larger than that obtained by single BL pyrolysis(62 wt%).LTF could avoid oxygen-containing functional groups from being excessively destroyed.It has nice regeneration performance by controlled combustion of char even after 5 cycles.     

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 influen...     

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.     

Promoting effect of microwave irradiation on CeO_2-TiO_2 catalyst for selective catalytic reduction of NO by NH_3

In this work we prepared several CeO₂-TiO₂ catalysts for the NH₃-SCR reactionusing co-precipitation with assistance of microwave irradiation. The catalytic NH₃-SCR activities over CeO₂-TiO₂ catalysts at low temperatures are largely enhanced by the treatment of microwave irradiation, the operation temperature window is also broadened. For better understanding the promotion mechanism, the catalyst prepared by conventional co-precipitation with and without microwave irradiation treatment was characterized with H₂-TPR, NH₃-TPD, XPS, XRD and BET. Microwave irradiation treatment accelerates the crystallite rate of CeO₂-TiO₂ catalysts, and greatly enlarges their surface area by adjusting their microstructures. The resistance to SO₂ and H₂O is also improved via regulating the hierarchical pore structure by the microwave irradiation. Microwave irradiation treatment can also improve the redox property and increase the acid sites over the catalyst surfaces. The result of in situ DRIFTS suggests that the microwave irradiation treatment generates more Brønsted acid sites on CeO₂-TiO₂-2 h catalyst, helpful in SCR reactions. XPS results show that after microwave irradiation on the CeO₂-TiO₂ catalysts, the surface demonstrates an elevated concentration of chemisorbed oxygen, consequently leading to better oxidation of NO to NO₂. Additionally, the molar ratio of Ce³⁺/Ce⁴⁺ has been elevated after being treated by microwave irradiation, a vital factor in enhancing the NH₃-SCR activities.     

CO2 sensing properties and mechanism of PrFeO3 and NdFeO3 thick film sensor

The CO_2 sensing of PrFeO_3 and NdFeO_3 sensors were investigated. Experimental results show that the resistances for PrFeO_3 and NdFeO_3 in CO_2 gas are larger than those in air and the responses for PrFeO_3and NdFeO_3 sensors increase with an increase in room-temperature relative humidity. When exposed to1000 ppm CO_2, the response of PrFeO_3 thick film based on nano-powders annealed at 700℃can reach8.44 at 160℃for the background of wet air with 58%of room-temperature relative humidity (RH),which is much larger than the corresponding value (3.03) in wet air with 25%RH. The sensing response S of NdFeO_3 thick-film sensor based on nano-powders annealed at 600℃to 3000 ppm CO_2 at the operating temperature 200℃can reach 2.36 for the background of wet air with 72%RH, which is larger than the corresponding value (1.83) in the air with 25%RH. Compared with other CO_2 sensing materials, the PrFeO_3 sensor has larger response at lower operating temperature for CO_2 gas and may be used as a new CO_2 sensing material.     

Effect of cerium oxide prepared under different hydrothermal time on electrocatalytic performance of Pt-based anode catalysts

In this paper,CeO_2 with a pore size of 2-4 nm was synthesized by hydrothermal method.The CeO_2 modified graphene-supported Pt catalyst was prepared by the microwave-assisted ethylene glycol reduction chloroplatinic acid method,and the effect of the addition of CeO_2 prepared by different hydrothermal reaction time on the catalytic performance of Pt-based catalysts was investigated.The microstructures of CeO_2 and catalysts were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),specific surface area and pore size analyzer(BET),scanning electron microscopy(SEM) and electron spectroscopy(EDAX),transmission electron microscopy(TEM),and the catalysts electrochemical performance was tested by electrochemical workstation.The results show that the catalytic performance of the four catalysts with CeO_2 is better than that of the catalyst without CeO_2.Adding CeO_2 with a specific surface area of 120.15 m~2/g prepared by hydrothermal reaction time of 39 h to Pt/C synthesis catalyst,its electrocatalytic performance,stability and resistance to poisoning are the best.The electrochemical active surface area is 102.83 m~2/g,the peak current density of ethanol oxidation is 757.17 A/g and steady-state current density of 1100 s is 108.17 A/g which shows the lowest activation energy for ethanol oxidation reaction.When the cyclic voltammogram is scanned for 500 cycles,the oxidation peak current density retention rate is 87.74%.     

Promoting effect and mechanism of neodymium on low-temperature selective catalytic reduction with NH3 over Mn/TiO2 catalysts

Series of Mn/TiO₂ catalysts modified with various contents of Nd for low-temperature SCR were synthesized. It can be found that the appropriate amount of Nd can markedly reduce the take-off temperature of Mn/TiO₂ catalyst to 80 °C and NO_x conversion is stabilized over 90% in the wide temperature range of 100–260 °C. 0.1Nd–Mn/Ti shows higher N₂ selectivity and better SO₂ resistance than Mn/Ti catalyst. The results reveal that Nd-doped Mn/TiO₂ catalyst exhibits larger BET surface area and better dispersion of active component Mn₂O₃. XPS results indicate that the optimal 0.1Nd–Mn/Ti sample possesses higher concentration of Mn⁴⁺ and larger amount of adsorbed oxygen at the surface compared with the unmodified counterpart. In situ DRIFTS show that the surface acidity is evidently increased after adding Nd, especially, the Lewis acid sites, and the intermediate (-NH₂) is more stable. The reaction mechanism over Mn/Ti and 0.1Nd–Mn/Ti catalysts obey the Eley-Rideal (E-R) mechanisms under low temperature reaction conditions. H₂-TPR results show that Nd–Mn/TiO₂ catalyst exhibits better low-temperature redox properties.     

Structure and luminescence properties of color-tunable phosphor Sr2La3(SiO4)3F:Tb3+,Sm3+

A series of single-phase and color-tunable phosphors Sr₂La₃(SiO₄)₃F:0.15Tb³⁺,xSm³⁺(SLSOF:0.15Tb³⁺,xSm³⁺) was prepared using solid-state route.The X-ray diffraction(XRD) was used to characterize the phase of the as-prepared samples.The synthesized phosphors have apatite-type structure without other impurities.Sm³⁺ and Tb³⁺ ions substitute La³⁺ into the lattice and form a single...     

Effect of tungsten oxide on ceria nanorods to support copper species as CO oxidation catalysts

In this work,tungsten oxide with different concentrations(0,0.4 at%,2.0 at% and 3.2 at%) was introduced to the ceria nanorods via a deposition-precipitation(DP) approach,and copper species of ca.10 at% were sequentially anchored onto the modified ceria support by a similar DP route.The aim of the study was to investigate the effect of the amount of tungsten oxide(0,0.4 at%,2.0 at%,and 3.2 at%) modifier on the copper-ceria catalysts for CO oxidation reaction and shed light on the structure-activity relationship.By the aids of multiple characterization techniques including N_2 adsorption,high-resolution transmission electron microscopy(HRTEM),powder X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),and temperature-programmed reduction by hydrogen(H_2-TPR) in combination with the catalytic performance for CO oxidation reaction,it is found that the copper-ceria samples maintain the crystal structure of the fluorite fcc CeO_2 phase with the same nanorod-like morphology with the introduction of tungsten oxide,while the textural properties(the surface area,pore volume and pore size) of ceria support and copper-ceria catalysts are changed,and the oxidation states of copper and tungsten are kept the same as Cu~(2+)and W~(6+)before and after the reaction,but the introduction of tungsten oxide(WO_3)significantly changes the metal-support interaction(transfer the CuO_x clusters to Cu-[O_x]-Ce species),which delivers to impair the catalytic activity of copper-ceria catalysts for CO oxidation reaction.     

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...     

Effect of impregnation strategy on catalytic hydrogenation behavior of PtCo catalysts supported on La2O2CO3 nanorods

Small Pt and Pt-Co nanoparticles (NPs) stabilized on La₂O₂CO₃ nanorods (LOC) were prepared by wet impregnation method, and probed in liquid-phase chemoselective hydrogenation of crotonaldehyde (CRAL) to crotyl alcohol (CROL). It is found that incorporation of Co atoms into Pt catalyst significantly improves the hydrogenation activity and desired selectivity to CROL as it destroys the Pt-lanthanum interfaces and results into the formation of Pt-Co particles. In addition, a close examination of catalyst surface and reactive performance suggests that the impregnation sequence of Pt and Co exerts great influence on the physicochemical property and the catalytic hydrogenation behavior of PtCo/LOC catalysts. As a result of the interaction between Pt and Co species, high alloying degree of Pt-Co NPs is obtained in the co-impregnated catalyst (Pt-Co/LOC), thus achieving the highest hydrogenation activity. The selective deposit of Co atoms onto the low-coordinated Pt sites leads to the smallest metal particle size and high dispersion of Pt-Co NPs over the Pt/Co/LOC, giving rise to the highest selectivity and yield to CROL.     

Effect of samarium and praseodymium addition on water gas shift performance of Co/CeO2 catalysts

The performance of Co supported over ceria and doped ceria (by Sm and Pr) catalysts towards the water gas shift reaction was studied for the removal of CO from syngas to produce high purity hydrogen for a fuel cell application. It is found that 1%Co/Ce-5%Sm-O yields the highest catalytic performance towards this reaction compared with undoped-Sm and doped-Pr. An addition of Sm onto ceria support reveals a small crystallite size with high surface area and well dispersed cobalt on ceria surface. Moreover, a presence of Sm increases the reducibility of cobalt species and surface oxygen. The positive effect of Sm on increasing the WGS activity of Co/CeO₂ is because Sm contributes to the reduction of Ce⁴⁺ to Ce³⁺ which gives rise to oxygen vacancies and facilitates the electron movement at the surface leading to an ease of surface reduction.     

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.     

Pseudo core-shell LaCoO_3@MgO perovskite oxides for high performance methane catalytic oxidation

Magnesia modified LaCoO_3 was prepared by a facile one-step sol-gel method and used for removal of dilute methane.Compared with the conventional doping technique,the obtained LaCoO_3@MgO-x exhibits pseudo core-shell structure and shows superior catalytic activity.The methane conversion exceeds90% at 532℃ on LaCoO_3@MgO-0.1,while only 60% of methane is conversed using the doped perovskite LaCo_(0.9)Mg_(0.1)O_3.The high catalytic performance of LaCoO_3@MgO-0.1 is mainly attributed to the adjustment of surface acid-base properties by the MgO shell structure.According to density functional theory(DFT) calculation,the methane is more likely to be adsorbed and cracked on LaCoO_3@MgO-0.1.The in situ DRIFTS shows that CH_3-O-CH_3 intermediate specie is formed.The pseudo core-shell structure also enhances the stability and the LaCoO_3@MgO-0.1 maintains high activity after working for 100 h.The above results demonstrate that surface modification by magnesia is an effective strategy for improving LaCoO_3 catalytic performance.     

Preparation of high performance YGdBCO films by low fluorine TFA-MOD process

YBCO films doped with different contents of gadolinium(Gd) were prepared by the low-fluorine(low-F)trifluoroacetate metal-organic deposition(MOD) method.The effects of flow rate and holding time of the firing(crystallization) stage on the superconducting properties of Y_xGd_(1-x)Ba_2 Cu_3 O_(7-δ)(YGdBCO) films were investigated.The phase formation and texture were characterized by the X-ray diffraction(XRD),which indicate that severe degradation of the microstructure will be induced with the inappropriate flow rate.The surface morphology and element distribution were investigated by the scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS).The results show that increasing the holding time of the firing stage is effective for the further decomposition of residual impurity phase on the surface.The mechanisms of the phase and surface evolution are also discussed.Finally,a high critical current density(J_c) value of 5.4 MA/cm~2 was achieved in the Y_(0.9)Gd_(0.1)BCO film fabricated by the cooperative control of the flow rate and holding time of the firing stage,which are contributed to the formation of excellent texture,homogeneous microstructure and dense surface of the YGdBCO films.     

Regulating local coordination environment of rhodium single atoms in Rh/CeO2 catalysts for N2O decomposition

Rh single atom catalysts(SACs) have been insensitively investigated recently due to the maximum utilization efficiency of Rh,one of the most expensive precious metals.Although great efforts have been made in the development and application of Rh SACs,there are few reports on the precise control of the local coordination environment of Rh single sites on CeO₂ and their catalytic performance for N₂O decomposition.Herein,Rh/CeO₂ catalysts with different Rh-O coordin...     

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.