Low-temperature SCR activity and SO_2 deactivation mechanism of Ce-modified V_2O_5–WO_3/TiO_2 catalyst

The promotion effect of ceria modi fi cation on the low-temperature activity of V2O5-WO3/TiO2 catalyst was evaluated for the selective catalytic reduction of NO with NH3(NH3-SCR). The catalytic activity of 1 wt% V2O5-WO3/TiO2 was signi fi cantly enhanced by the addition of 8 wt%ceria, which exhibited a NO x conversion above 80% in a broad temperature range 190–450 1C. This performance was comparable with 3 wt%V2O5-WO3/TiO2, indicating that the addition of ceria contributed to reducing the usage of toxic vanadia in developing low-temperature SCR catalysts. Moreover, V1 Ce WTi exhibited approximately 10% decrease in NOx conversion in the presence of 60 ppm SO2. The characterization results indicated that active components of V, W and Ce were well dispersed on TiO2 support. The synergetic interaction between Ce and V species by forming V–O–Ce bridges enhanced the reducibility of VCe WTi catalyst and thus improved the low-temperature activity. The sulfur poisoning mechanism was also presented on a basis of the designed TPDC(temperature-programmed decomposition) and TPSR(temperatureprogrammed surface reaction) experiments. The deposition of(NH4)2SO4on V1 Ce WTi catalyst was much smaller compared with that on V1 Ti.On the other hand, the oxidation of SO2 to SO3was signi fi cantly promoted on the CeO2-modi fi ed catalyst, accompanied by the formation of cerium sulfates. Therefore, the deactivation of this catalyst was mainly attributed to the vanishing of the V–Ce interaction and the sulfation of active ceria.     

The influence of molar ratios of Ce/Zr on the selective catalytic reduction of NOx with NH3 over Fe2O3-WO3/CexZrl-xO2 （0 〈 x 〈 1） monolith catalyst

A series of CexZrl_xO2 （0 ≤ x ≤ 1） with dif- ferent molar ratios of Ce/Zr were syhthesized via coprecip- itation method, and Fe2O3-WO3/CexZrl-xO2 monolithic catalysts were prepared, for selective catalytic reduction of nitrogen oxides by ammonia （NH3-SCR）. The structural properties and redox behavior of the catalysts were com- prehensively characterized by N2 physisorption, X-ray diffraction （XRD）, X-ray photoelectron spectra （XPS）, H2-temperature programmed reduction （H2-TPR） and activity measurement for NH3-SCR. The results showed that the NH3-SCR activities of the catalysts were gradually enhanced by increasing the molar ratios of Ce/Zr, especially the low- temperature catalytic activity and the reaction temperature window. Fe2O3-WO3/Ceo.68Zro.3202 monolithic catalyst presented the best NH3-SCR activity among the investigated catalysts, more than 90 % NOx could be removed in the temperature range of 247-454 ℃ on the catalyst under the gas hourly space velocities of 30,000 h- 1. And it always held more than 99 % N2 selectivity and less than 20 ppm （1 ppm =10-6 L/L ） N20 generation concentration between 200 and 500 ℃, the catalyst also displayed its strong resistance of H20 and SO2. Good textural and structural properties, more surface Fe, Ce and active oxygen were together contributed to the excellent NH3-SCR performance of Fe2O3-WO3/ Ce0.68Zr0.32O2 catalyst.     

The poisoning and regeneration effect of alkali metals deposed over commercial V2O5-WO3/TiO2 catalysts on SCR of NO by NH3

In this study, commercial V2O5-WO3/TiO2 catalysts were deactivated by loading with alkali metals （K and Na）. These catalysts were then regenerated by washing with either deionized water or 0.5 mol/L H2SO4 （through the ultrasonic-assisted method）. The samples used in this research were characterized by NH3-temperature programmed desorption （TPD）, and X-ray photoelectron spectroscopy （XPS）. Results showed that Na2O and KaO doping can poison the V2O5-WO3/TiO2 catalyst and that the poisoning effect of Na2O was stronger than that of KaO. However, the Na2O-loaded sample was easier to regenerate than the KaO-loaded sample. The surfaces of catalysts can be sulfated by washing with dilute sulfuric acid because strong acid sites adhere to the catalyst surface. SO42- could also promote catalyst activity. As indicated by the NH3-TPD findings, the deposition of Na2Oand K2O could also reduce the amount of desorbed ammonia and destabilize the acid sites, especially strong chemisorption sites. XPS results revealed that catalysts were deactivated by the decrease in the concentration of chemisorbed oxy- gen [the Oα（Oα ＋ Oβ） ratio]. In the Na2O-doped catalyst, much chemisorbed oxygen was lost （from 28.8 % to 10.6 %）. However, the decrease in the Oα（Oα ＋ Oβ） ratio was less significant in the K20-doped catalyst （from 28.8 % to 23.5 %）. Nonetheless, the binding energies of Ols broadened with respect to both high and low energy. Inparticular, the binding energy of chemisorbed oxygen increased from 531.5 to 531.8 eV.     

Effects of CeO_2 pre-calcined at different temperatures on the performance of Pt/CeO_2–C electrocatalyst for methanol oxidation reaction

Pt/CeO2–C catalysts with CeO_2 pre-calcined at 300–600°C were synthesized by combining hydrothermal calcination and wet impregnation. The effects of the pre-calcined CeO_2 on the performance of Pt/CeO_2–C catalysts in methanol oxidation were investigated. The Pt/CeO2–C catalysts with pre-calcined CeO_2 at 300–600°C showed an average particle size of 2.6–2.9 nm and exhibited better methanol electro-oxidation catalytic activity than the commercial Pt/C catalyst. In specific, the Pt/CeO_2–C catalysts with pre-calcined CeO_2 at 400°C displayed the highest electrochemical surface area value of 68.14 m~2·g~(-1) and If/Ib ratio(the ratio of the forward scanning peak current density(If)and the backward scanning peak current density(Ib)) of 1.26, which are considerably larger than those(53.23 m2·g~(-1) and 0.79, respectively) of the commercial Pt/C catalyst, implying greatly enhanced CO tolerance.     

Pt-induced electrochemical growth of ZnO rods onto reduced graphene oxide for enhanced photodegradation performance

Photodegradation of organic pollutants over semiconductor catalysts is considered to be a viable method for wastewater treatment.Of the different semiconductor photocatalysts,ZnO has been widely used for the photodegradation of organic pollutants.Meanwhile,graphene is being actively investigated as a cocatalyst for such processes.The high carrier transport rate of graphene can favor the transfer of photoexcited electrons,while the increased specific surface area provides adsorption sites for the organic effluent molecules,thereby improving overall photocatalytic activity.Therefore,in this study,Pt–ZnO–reduced graphene oxide(RGO)rods with different RGO contents are synthesize during a novel Pt-induced electrochemical method,where ZnjZnO acts as the anode and PtjH2OjH2acts as the cathode.The photocatalytic degradation activity of the Pt–ZnO–RGO rods is remarkably improved under UV–visible light irradiation,with the optimum loading RGO content of 1 wt%.     

Effects of baria on propane oxidation activity of Pd/Al2O3 catalyst: Pd–BaO interactio n and reaction routes

The BaO-modified Pd/Al2O3exhibits much better catalytic activity than Pd/Al2O3for C3H8 oxidation both before and after the hydrothermal aging treatment. Further studies ascribe its good activity to the influence of BaO species on the physicochemical characteristics of the catalyst and the reaction routes. Firstly, the BaO species inhibits the phase transformation of alumina, resulting in higher surface area of the catalysts and hereby a better dispersion of Pd. Secondly, the basic nature and electron-withdrawing effect of barium oxide maintain palladium at high oxidation state, which leads to a higher PdO content on surface of the BaO-modified catalyst. Finally, the formation/decomposition of carbonate/bicarbonate species can be promoted by the addition of BaO, which provide extra reaction routes and are important for the deep oxidation of C3H8.     

Activity coefficient of NiO in SiO2-saturated MnO–SiO2slag and Al2O3-saturated MnO–SiO2–Al2O3slag at 1623 K

As a part of the fundamental study related to the reduction smelting of spent lithium-ion batteries and ocean polymetallic nodules based on MnO–SiO₂slags,this work investigated the activity coefficient of NiO in SiO₂-saturated Mn O–Si O₂slag and Al₂O₃-saturated Mn O–SiO₂–Al₂O₃slag at 1623 K with controlled oxygen partial pressure levels of 10^-7,10^-6,and 10^-5Pa.Results showed that the solubility of nickel oxide in the slags increased with increasing oxygen partial pressure.The nickel in the Mn O–Si O₂slag and Mn O–Si O₂–Al₂O₃slag existed as Ni O under experimental conditions.The addition of Al₂O₃in the Mn O–Si O₂slag decreased the dissolution of nickel in the slag and increased the activity coefficient of Ni O.Furthermore,the activity coefficient of Ni O(γN_(i O)),which is solid Ni O,in the Si O₂saturated Mn O–Si O₂slag and Al₂O₃saturated Mn O–Si O₂–Al₂O₃slag at 1623 K can be respectively calculated asγN_(i O)=8.58w(Ni O)+3.18 andγN_(i O)=11.06w(Ni O)+4.07,respectively,where w(Ni O)is the Ni O mass fraction in the slag.     

Theoretical study of adsorption and dissociation of NH_3 on the Ir{110}(1×2) surface

The adsorption and dissociation of NH3 on Ir{110}(1×2) have been investigated using the densityfunctional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}(1×2) was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}(1×2) are very competitive, which is consistent with the recent experimental results.     

Theoretical study of adsorption and dissociation of NH3 on the Ir{110}（1×2） surface

The adsorption and dissociation of NH3 on Ir{110}（1×2） have been investigated using the density- functional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}（1×2） was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}（1×2） are very competitive, which is consistent with the recent experimental results.     

Effect of B sites on the catalytic activities for perovskite oxides La_(.6)Sr_(.4)Co_xFe_(1-x)O_(3-δ) as metal-air batteries catalysts

The effect of B sites on the catalytic activities of oxygen evolution reaction(OER)for perovskite oxides La_(0.6)Sr_(0.4)Co_xFe_(1-x)O_(3-δ)(x=0,0.2,0.4,0.6,0.8,1,denoted as LSF,LSCF-28,LSCF-46,LSCF-64,LSCF-82 and LSC,respectively)prepared by a convenient and simple method of electrospinning technique is reported.The prepared La_(0.6)Sr_(0.4)Co_xFe_(1-x)O_(3-δ)catalysts possess almost same crystal structures,similar morphologies(except for the LSC catalyst)and slightly different BET surface areas.Upon the optimization of the Co/Fe atomic ratio,the optimal LSCF-82 catalyst exhibits the OER performance with a low onset potential of 1.541 V,a small Tafel slope of 80.56 mV dec~(-1),a high charge-transfer rate and a large electrochemical surface area in 0.1 M KOH solution.LSCF-82 catalyst exhibits the long-term stability under the catalytic operation condition for 12 h.Such catalytic activity may mainly cause by the synergy of higher catalytic activity Co and lower catalytic activity Fe.Thus,the reasonable optimization of the transition metal composition in B sites for the perovskite oxides is in favor of the improvement of OER performance.     

Effect of TiO_2 nanoparticles on hydrogen evolution reaction activity of Ni coatings

The electrocatalytic activity of electrodeposited Ni and Ni–TiO_2 coatings with regard to the alkaline hydrogen evolution reaction(HER) was investigated. The Ni coatings were electrodeposited from an acid chloride bath at different current densities, and their HER activities were examined in a 1.0-mol·L~(-1) KOH medium. The variations in the HER activity of the Ni coatings with changes in surface morphology and composition were examined via the electrochemical dissolution and incorporation of nanoparticles. Electrochemical analysis methods were used to monitor the HER activity of the test electrodes; this activity was confirmed via the quantification of gases that evolved during the analysis. The obtained results demonstrated that the Ni–TiO_2 nanocomposite test electrode exhibited maximum activity toward the alkaline HER. The surface appearance, composition, and the phase structure of all developed coatings were analyzed using scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), and X-ray diffraction(XRD), respectively. The improvement in the electrocatalytic activity of Ni–TiO_2 nanocomposite coating toward HER was attributed to the variation in surface morphology and increased number of active sites.     

Activity coefficients of NiO and CoO in CaO–Al_2O_3–SiO_2 slag and their application to the recycling of Ni–Co–Fe-based end-of-life superalloys via remelting

To design optimal pyrometallurgical processes for nickel and cobalt recycling, and more particularly for the end-of-life process of Ni–Co–Fe-based end-of-life(EoL) superalloys, knowledge of their activity coefficients in slags is essential. In this study, the activity coefficients of NiO and CoO in CaO–Al_2O_3–SiO_2 slag, a candidate slag used for the EoL superalloy remelting process, were measured using gas/slag/metal equilibrium experiments. These activity coefficients were then used to consider the recycling efficiency of nickel and cobalt by remelting EoL superalloys using CaO–Al_2O_3–SiO_2 slag. The activity coefficients of NiO and CoO in CaO–Al_2O_3–SiO_2 slag both show a positive deviation from Raoult's law, with values that vary from 1 to 5 depending on the change in basicity. The activity coefficients of NiO and CoO peak in the slag with a composition near B =(%CaO)/(%SiO_2) = 1, where B is the basicity. We observed that controlling the slag composition at approximately B = 1 effectively reduces the cobalt and nickel oxidation losses and promotes the oxidation removal of iron during the remelting process of EoL superalloys.     

CeO2: an active and selective catalyst for the oxidative dehydrogenation of ethane with CO2

It was assumed that the homogeneous dehydrogenation of CiHg occurred in the gas phase was independent of the presence of catalysts and this is applicable to the oxidative dehydrogenation of ethane with CO2 over CeO2 . On the basis of this assumption, a method was developed to analyze the contribution of C2rtj formation from heterogeneous catalysis. In this study, ceria was found to be active and selective for the oxidative dehydrogenation of ethane with CO2 and the selectivity to C, H4 was above 60 % and the actual contribution for C, H4 formation from heterogeneous catalysis was about 55%— 75% in the range of 953—993 K.     

Synthesis of a new meso／microporous composite molecular sieve of MCM-41／mordenite

An MCM-41/mordenite composite with twofold porous structure and stepwise-distributed acidity was prepared for the first time by using zeolite mordenite as the silica-alumina source. The composite molecular sieve has been investigated and compared with a mechanical mixture of mordenite and MCM-41 for their structure, acidity and catalytic activity by means of XRD, N2 adsorption and desorption, HRTEM, DTG, NH3-TPD and catalytic reaction. The characterization results show that the structure and property of the composite molecular sieve are quite different from those of the mechanical mixture, which might be ascribed to the incorporation of secondary building units characteristic of zeolite mordenite into the mesoporous walls of the composite which gives rise to the thicker mesoporous walls, the higher hydrothermal stability and more strong acid sites. Furthermore, the new strategy could be used as a new general method for the preparation of catalysts for the reaction system with multifold large molecules, and the results were well confirmed by the dealkylation of C10^ aromatic hydrocarbon.     

Highly dispers ed iron species created on alkali-treated zeolite for ammonia SCR

Alkaline treatment using sodium hydroxide was introduced to obtain a hierarchical pore structure in H-ZSM-5 zeolite.Fe-exchanged zeolite catalysts were prepared by impregnation on the original and alkali-treated zeolites,and were evaluated for NOx reduction by NH3,NO oxidation,and NH3 oxidation reactions.The highly dispersed iron species as active sites can be obtained by controlling the pore structure and particle size of zeolite.Therefore,the Fe/ZSM-5 catalyst treated mildly by sodium hydroxide before iron exchange,which contains amounts of highly dispersed Fe species,obtains over80% NOx conversion at a wide temperature range of 250-500℃.     

不同温度下CeO2预煅烧对甲醇氧化反应中Pt/CeO2–C电催化剂性能的影响

Pt/CeO₂–C catalysts with CeO₂ pre-calcined at 300–600°C were synthesized by combining hydrothermal calcination and wet impregnation. The effects of the pre-calcined CeO₂ on the performance of Pt/CeO₂–C catalysts in methanol oxidation were investigated. The Pt/CeO₂–C catalysts with pre-calcined CeO₂ at 300–600°C showed an average particle size of 2.6–2.9 nm and exhibited better methanol electro-oxidation catalytic activity than the commercial Pt/C catalyst. In specific, the Pt/CeO₂–C catalysts with pre-calcined CeO₂ at 400°C displayed the highest electrochemical surface area value of 68.14 m2·g?1 and I_f/I_b ratio (the ratio of the forward scanning peak current density (I_f) and the backward scanning peak current density (I_b)) of 1.26, which are considerably larger than those (53.23 m2·g?1 and 0.79, respectively) of the commercial Pt/C catalyst, implying greatly enhanced CO tolerance.     

Selective catalytic reduction of NO x by hydrogen over modified Pd/TiO2-Al2O3 catalyst under lean-burn conditions

A series of Ni, Sn and Ca modified Pd/TiO2-Al2O3 catalysts were prepared by the incipient wetness impregnation method and their catalytic performance for the selective catalytic reduction of NOx by H2 was evaluated. The results showed that the NOx conversion and N2 selectivity were improved over Pd-Sn/TiO2-Al2O3 and Pd-Ni/TiO2- Al2O3 catalysts above 200 ℃. More importantly, the N2 selectivity and high-temperature activity of Pd-Sn/TiO2- Al2O3 catalyst was far superior to the single Pd/TiO2-Al2O3 catalyst. The optimal Sn loading was 2 wt.%. X-ray diffrac- tion （XRD） results showed that the interaction between Pd and Sn promotes the dispersion of Pd over TiO2-Al2O3. Temper- ature-programmed reduction （Ha-TPR） results demonstrated that the addition of Sn contributes to the formation of PdO and improving the redox property of Pd/TiOz-Al2O3. The addi- tives of Ni and Sn also facilitated the absorption of NOx and the oxidation of NO to NOa, which play important roles in the selective catalytic reduction of NOx by hydrogen.     

DFT investigation of NH3 gas interactions on TeO2 nanostructures

The structural, electronic and adsorption properties of NH_3 on pristine, Sn and F substituted TeO_2 nanostructures were investigated using density functional theory with B3LYP/Lan L2 DZ basis set. The electronic properties of pristine, Sn and F incorporated TeO_2 nanostructures were explained with ionization potential, HOMO–LUMO gap and electron af fi nity. The dipole moment and point group of rutile TeO_2 nanostructures were also reported. The structural stability of pristine, Sn and F substituted TeO_2 nanostructures were investigated in terms of formation energy. The adsorption properties of NH3 on TeO_2 were studied and the proper adsorption sites of NH_3 on TeO_2 materials were identi fi ed and discussed with the suitable parameters such as adsorption energy, HOMO–LUMO gap, Mulliken population analysis and average energy gap variation. The results show that the substitution of fl uorine in TeO_2 nanostructure enhances NH3 adsorption properties in mixed gas environment.     

Development of CMAQ for East Asia CO2 data assimilation under an EnKF framework: a first result

Under an Ensemble Kalman Filter(EnKF)framework,Regional Atmospheric Modeling System and Models-3 Community Multi-scale Air Quality(RAMS–CMAQ)modeling system is developed to be a CO2data assimilation system EnKF–CMAQ,and the EnKF–CMAQ system is then applied to East Asia for validation with real continuous surface CO2concentration observations available in the study domain instead of using an observation simulation system experiment.Experiments with an experimental period of January 23 to February 7,2007 are conducted,and the experimental results of the EnKF–CMAQ system and the RAMS–CMAQ model are compared against continuous surface CO2observations from assimilation sites and independent reference sites.Distributions of daily mean CO2concentration increments show that the EnKF–CMAQ system confines the update of daily mean CO2within areas nearby and downwind of the assimilation sites.Both the CO2concentration ensemble spreads and background error covariances show flow-dependent patterns.The results indicate the crucial role of wind transport in the CO2data assimilation,which agrees with the previous studies.The average bias and the average root-mean-square error(RMSE)of daily mean CO2concentration at the assimilation sites are reduced by 1.00 and1.83 ppm,respectively,and those at the reference sites are reduced by 0.24 and 0.22 ppm,respectively.The results demonstrate the EnKF–CMAQ system is capable of assimilating the continuous surface CO2concentration observations to improve the simulation accuracy of the atmospheric CO2synoptic variation.Since growing CO2observations over East Asia are being available nowadays,this work is our first step to generate consistent spatial and temporal atmospheric CO2concentration fields over East Asia,particularly over China,using both in situ and satellite observations.     

Catalytic combustion properties of nanocomplex oxide for natural gas

The catalysts of copper oxide supported on cerium dioxide were prepared by different methods for methane catalytic combustion. The effects of copper content in the catalysts and calcination temperatures of the catalysts on the catalytic activity are investigated. Results show that the complex oxide catalyst exhibits high catalytic activity for methane combustion due to the synergistic effect of CuO and CeO₂. The catalyst prepared by impregnation is more active than that prepared by controlled coprecipitation even if CuO content is the same. When W(CuO)<13%, the light-off temperature and full conversion temperature for the CH₄ reaction decrease with the increasing of CuO content in the catalysts. However, when the copper content is above 13%, the excess CuO has a negative effect on the catalytic activity owing to the formation of bulk CuO particles. A proper calcinations temperature of 650 ℃ can lead to a high dispersion of CuO and accordingly can enhance the catalytic activity of the composites.