Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag/SiO_(2) Catalysts for CO Selective Oxidation in H_(2)

The interactions of oxygen with pre-reduced silver catalysts as well as theircatalytic properties for CO selective oxidation in H_2 after oxygen pre-treatment are studied inthis paper. It is found that the pretreatment exerts a strong influence on the activity andselectivity of the silver catalyst. A drop in activity and selectivity is observed after treating apre-reduced catalyst with oxygen at low temperatures, whereas a converse result is obtained after anoxidizing treatment at high temperatures (T ≥ 350℃). O_2-TPD results show that surface oxygenspecies adsorbs on silver surface after the oxygen treatment at low temperatures. However,penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile thesurface oxygen species disappear. No other silver species except metallic silver are observed on allthe catalysts by XRD, and the size of silver particle is not changed after the treatment withoxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also beremoved by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorptionand diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing thedecrease in CO oxidation activity, in other words, it is important to obtain a clean silver surfacefor increasing the catalyst activity in CO removal from H_2-rich feed gas. The differences inactivity and selectivity due to the oxygen pretreatment at different temperatures are discussed interms of the changes in the surface/subsurface oxygen species of the silver particles.

Catalytic Oxidation of Toluene over Nanorod Manganese Oxides Catalysts: Phase Change Effects

Four manganese oxide (MnO_(x)) catalysts with different phases were prepared via a hydrothermal method, and the toluene oxidation over the four manganese dioxide (MnO_(x)) catalysts was studied. Among the catalysts, δ-MnO_(2) exhibits the best performance, excellent stability, and reusability. Moreover, δ-MnO_(2) possesses the highest specific surface area, with more exposed active sites compared to the other catalysts with which to make contact with toluene, leading to it exhibiting excellent activity. Furthermore, δ-MnO_(2) shows more lattice defects, Mn^(3+)/(Mn^(3+) + Mn^(4+)), oxygen vacancies, and surface adsorbed oxygen than the other catalysts, resulting in its excellent redox properties and catalytic performance. In addition, oxygen molecules adsorb on the oxygen vacancies of δ-MnO_(2), which are beneficial to the adsorption and oxidation of toluene, with benzyl alcohol, benzaldehyde, benzoic acid, and benzoic acid ester detected as specific intermediate products.

Selective catalytic oxidation of NO with O_2 over Ce-doped MnO_x/TiO_2 catalysts

A series of Ce-doped MnOx/TiO2 catalysts were prepared by impregnation method and used for catalytic oxidation of NO in the presence of excess O2. The sample with the Ce doping concentration of Ce/Mn=l/3 and calcined at 300 ℃ shows a superior activity for NO oxidation to NO2. On Ce（1）Mn（3）Ti catalyst, 58% NO conversion was obtained at 200 ℃ and 85% NO conversion at 250 ℃ with a GHSV of 41000 h-1, which was much higher than that over MnOx/TiO2 catalyst （48% at 250 ℃）. Characterization results implied that the higher activity of Ce（1）Mn（3）Ti could be attributed to the enrichment of well-dispersed MnO2 on the surface and the abundance of Mn3＋ and Zi3＋ species. The addition of Ce into MnO2/TiO2 could improve oxygen storage capacity and facilitate oxygen mobility of the catalyst as shown by PL and ESR, so that its activity for NO oxidation could be enhanced. The effect of H2O and SO2 on the catalyst activity was also investigated.

Experimental Research on Mercury Catalytic Oxidation over Ce Modified SCR Catalyst

In order to improve the ability of SCR catalyst to catalyze the oxidation of gaseous elemental mercury,a series of novel Ce modified SCR(Selection Catalytic Reduction,V_(2)O_(5)-WO_(3)/TiO_(2))catalysts were prepared via two-step ultrasonic impregnation method.The performance of Ce/SCR catalysts on Hg^(0)oxidation and NO reduction as well as the catalytic mechanism on Hg^(0)oxidation was also studied.The XRD,BET measurements and XPS were used to characterize the catalysts.The results showed that the pore volume and pore size of catalyst was reduced by Ce doping,and the specific surface area decreased with the increase of Ce content in catalyst.The performance on Hg^(0)oxidation was promoted by the introduction of CeO_(2).Ce_(1)/SCR(1%Ce,wt.%)catalyst exhibited the best Hg^(0)oxidation activity of 21.2%higher than that of SCR catalyst at 350℃,of which the NO conversion efficiency was also higher at 200-400℃.Furthermore,Ce_(1)/SCR showed a better H_(2)O resistance but a slightly weaker SO_(2)resistance than SCR catalyst.The chemisorbed oxygen and weak absorbed oxygen on the surface of catalyst were increased by the addition of CeO_(2).The chemisorbed oxygen and weak absorbed oxygen on the surface of catalyst were increased by the addition of CeO_(2).The Ce_(1)/SCR possed better redox ability compared with SCR catalyst.HCl was the most effective gas responsible for the Hg^(0)oxidation,and the redox cycle(V^(4+)+Ce^(4+)←→V^(5+)+Ce^(3+))played an important role in promoting Hg^(0)oxidation.

Pt/FeSnO(OH)_5： A Novel Supported Pt Catalyst for Catalytic Oxidation of Benzene

Pt/FeSnO（OH）_5 was synthesized as a novel catalyst for VOCs oxidation. Compared with Pt/γ-Al_2O_3 during catalytic oxidation of benzene, Pt/Fe Sn O（OH）5 showed better catalytic activity. After characterization of the catalysts by XRD, SEM, TEM, EDS, XPS, BET, TGA and DTA, we found most Pt could be reduced to metallic state when the hydroxyl catalyst was used as supporter, and the metallic Pt in Pt/Fe Sn O（OH）5 was more active than the oxidized Pt in Pt/γ-Al_2O_3 in catalytic oxidation of VOCs. Pt/FeSnO（OH）_5 shows both good catalytic activity and high stability, which may be a promising catalyst. This study may also be helpful for the design and fabrication of new catalysts.

Preparation of nitric humic acid by catalytic oxidation from Guizhou coal with catalysts

Nitric humic acid was prepared by catalytic oxidation between nitric acid and Guizhou coal, with added catalysts. We investigated catalytic oxidation processes and the factors that affect the reactions. The effects of different catalysts, including NiSO 4 support on active carbon (AC-NiSO 4 ), NiSO 4 support on silicon dioxide (SiO 2 -NiSO 4 ), composites of SO 4 2à /Fe 2 O 3 , Zr-iron and vanadium-iron composite were studied. As well, we investigated nitric humic acid yields and the chemical structure of products by element analysis, FT-IR and E4/E6 (an absorbance ratio at wavelengths of 465 and 665 nm of humic acid alkaline extraction solutions). The results show that the catalytic oxidation reaction with added catalysts can increase humic acid yields by 18.7%, 16.36%, 12.94%, 5.61% and 8.59%, respectively. The highest yield of humic acid, i.e., 36.0%, was obtained with AC-NiSO 4 as the catalyst. The amounts of C and H decreased with the amount of nitrogen. The increase in the E4/E6 ratio in catalytic oxidation of (Guizhou) coal shows that small molecular weights and high yields of nitric humic acid can be obtained by catalytic oxidation reactions.

Advances in selective catalytic oxidation of ammonia (NH_(3)-SCO): A review of catalyst structure-activity relationship and design principles

NH_(3) in ambient air directly leads to an increase in the aerosol content in the air. These substances lead to the formation of haze to various environmental problems after atmospheric circulation and diffusion. Controlling NH_(3) emissions caused by ammonia escaping from mobile and industrial sources can effectively reduce the NH_(3) content in ambient air. Among the various NH_(3) removal methods, the selective catalytic oxygen method (NH_(3)-SCO) is committed to oxidizing NH_(3) to environmentally harmless H_(2)O and N_(2);therefore, it is the most valuable and ideal ammonia removal method. In this review, the characteristics of loaded and core-shell catalysts in NH_(3)-SCO have been reviewed in the context of catalyst structure-activity relationships, and the H_(2)O resistance and SO2 resistance of the catalysts are discussed in the context of practical application conditions. Then the effects of the valence state of the active center, oxygen species on the catalyst surface, dispersion of the active center and acidic sites on the catalyst performance are discussed comprehensively. Finally, the shortcomings of the existing catalysts are summarized and the catalyst development is discussed based on the existing studies.

Study on Chemisorption, Catalytic Behavior, and Stability of Supported Au Catalyst for the Propylene Epoxidation Reaction

The supported Au/TiO2 and Au/TiO2-SiO2 catalysts were prepared by deposition precipitation method. The TPD study reveals that propylene oxide competes with propylene to be adsorbed on the same adsorptive center-Ti^n＋ site on the surface of the catalyst and that the adisorbing capacity of the catalyst for propylene oxide is larger than that for propylene. Catalytic behavior for propylene epoxidation with H2 and O2 was tested in a micro-reactor. Under typical conditions, the selectivity for propylene oxide is over 87%. The TG curves show that PO successive oxidation cause carbon deposition on the active center and deactivation of the Au catalysts. Because the amounts of Tin＋ site decrease significantly, and consequently the separation between Ti^n＋ sites increases, the Au/TiO2-SiO2 catalyst is more stable than Au/TiO2.

A highly hydrothermal stable copper-based catalyst for catalytic wet air oxidation of m-cresol in coal chemical wastewater

Catalytic wet air oxidation(CWAO) can degrade some refractory pollutants at a low cost to improve the biodegradability of wastewater. However, in the presence of high temperature and high pressure and strong oxidizing free radicals, the stability of catalysts is often insufficient, which has become a bottleneck in the application of CWAO. In this paper, a copper-based catalyst with excellent hydrothermal stability was designed and prepared. TiO_(2) with excellent stability was used as the carrier to ensure the longterm anchoring of copper and reduce the leaching of the catalyst. The one pot sol–gel method was used to ensure the super dispersion and uniform distribution of copper nanoparticles on the carrier, so as to ensure that more active centers could be retained in a longer period. Experiments show that the catalyst prepared by this method has good stability and catalytic activity, and the catalytic effect is not significantly reduced after 10 cycles of use. The oxidation degradation experiment of m-cresol with the strongest biological toxicity and the most difficult to degrade in coal chemical wastewater was carried out with this catalyst. The results showed that under the conditions of 140℃, 2 MPa and 2 h, m-cresol with a concentration of up to 1000 mg·L^(-1) could be completely degraded, and the COD removal rate could reach 79.15%. The biological toxicity of wastewater was significantly reduced. The development of the catalyst system has greatly improved the feasibility of CWAO in the treatment of refractory wastewater such as coal chemical wastewater.

Kinetics study on catalytic wet air oxidation of phenol by several metal oxide catalysts

Four metal oxide catalysts composed of copper(Cu), stannum(Sn), copper-stannum(Cu-Sn) and copper-cerium(Cu-Ce) respectively were prepared by the co-impregnation method, and γ-alumina(γ-Al 2O 3) is selected as support. A first-order kinetics model was established to study the catalytic wet air oxidation of phenol at different temperature when these catalysts were used. The model simulations are good agreement with present experimental data. Results showed that the reaction rate constants can be significantly increased when catalysts were used, and the catalyst of 6% Cu—10%Ce/γ-Al 2O 3 showed the best catalytic activity. This is consistent with the result of catalytic wet air oxidation of phenol and the COD removal can be arrived at 98.2% at temperature 210℃, oxygen partial pressure 3 MPa and reaction time 30 min. The activation energies of each reaction with different catalysts are nearly equal, which is found to be about 42 kJ/mol and the reaction in this study is proved to be kinetics control.

The high catalytic activity and strong stability of 3%Fe/AC catalysts for catalytic wet peroxide oxidation of m-cresol: The role of surface functional groups and FeO_(x) particles

FeO;supported on activated carbon(AC) has been shown to be an ideal catalyst for catalytic wet peroxide oxidation(CWPO) due to its high CWPO reaction activity and stability. Although there have been some studies on the mechanism of Fe/AC catalysis in CWPO, the specific contribution of each component(surface oxygen groups and FeOxon AC) inside an Fe/AC catalyst and their corresponding reaction mechanism remain unclear, and the reaction stability of CWPO catalysts has rarely been discussed. Then the optimal CWPO catalyst in our laboratory, 3%Fe/AC, was selected.(1) By removing certain components on the AC through heat treatment, its contribution to the reaction and the corresponding reaction mechanism were investigated. With the aid of temperature-programmed desorption–mass spectrometry(TPD–MS) and the CWPO reaction, the normalized catalytic contributions of components were shown to be: 37.3%(carboxylic groups), 5.3%(anhydride), 19.3%(ether/hydroxyl),-71.4%(carbonyl groups) and 100%(FeOx),respectively. DFT calculation and EPR analysis confirmed that carboxylic groups and Fe_(2)O_(3) are able to activate the H_(2)O_(2) to generate·OH.(2) The catalysts at were characterized at different reaction times(0 h, 450 h, 900 h, 1350 h, and 1800 h) by TPD–MS and M?ssbauer spectroscopy. Results suggested that the number of carboxylic goups gradually increased and the size of paramagnetic Fe_(2)O_(3) particle crystallites gradually increased as the reactions progressed. The occurrence of strong interactions between metal oxides and AC was also confirmed. Due to these effects, the strong stability of 3%Fe/AC was further improved. Therefore, the reasons for the high activity and strong stability of 3%Fe/AC in CWPO were clearly shown. We believe that this work provides an idea of the removal of cresols from wastewater into the introduction to show the potential applications of CWPO.

Influence of the structure of TiO_2 , CeO_2 , and CeO_2-TiO_2 supports on the activity of Ru catalysts in the catalytic wet air oxidation of acetic acid

Ru catalysts, supported on TiO 2 , CeO 2 , and CeO 2 -TiO 2 , were prepared by the impregnation method. The effect of the structure of the supports on the activity of Ru catalysts was investigated in the catalytic wet air oxidation （CWAO） of acetic acid under 230℃ and 5 MPa in a batch reactor. Physical properties including the surface area, crystalline phase, and surface components of the Ru catalysts were characterized by N 2 adsorption, X-ray powder diffraction （XRD）, and X-ray photoelectron spectroscopy （XPS）. The CeO 2 -based Ru catalysts had good activity, and the prepared RuO 2 /CeO 2 catalyst showed markedly higher activity than the RuO 2 /CeO 2 -TiO 2 catalyst. The surface structure, the high amount of chemisorbed oxygen on the catalyst surface, and the suitable pH pzc value of the supports played an important role in the activity of the Ru catalysts in CWAO of acetic acid.

Preparation of Au/CeO_2 catalyst and its catalytic performance for HCHO oxidation

Aqueous precipitation and deposition-precipitation method were used to prepare CeO2 supports and Au/CeO2 catalysts, respectively. The effect of preparation condition of support on the catalyst activity was investigated. The catalytic combustion of HCHO was considered as the probe reaction for comparing the catalyst activity. The BET, X-ray diffraction, X-ray photoelectron spectroscopy （XPS）, and reduction （TPR） were carried out to analyze the influence factor on the catalysts activity. The results showed that the addition of dispersant and use of microwave in the support preparation procedure could be beneficial for enhancing the interaction of supports and gold species and thus improved the catalytic activity. The total conversion temperature for HCHO was 146 ℃ over AC400. With the modification during supports preparation process, the catalytic activity increased with total conversion temperature decreasing to 98 ℃. The results of XPS indicated that Au^0 and Au^＋1 species coexisted in these catalysts and the activity of catalyst correlated with Au^＋1/Au^0 ratio. Temperature-programmed reduction results demonstrated that the reduction peak appeared between 100-170 ℃ with the inducing of gold. The dependence of activity on the reduction peak temperature implied that ionic gold was catalytic activity component for HCHO oxidation.

Preparation of Cerium Doped Cu/MIL-53(A1) Catalyst and Its Catalytic Activity in CO Oxidation Reaction

Metal-organic framework（MOF） material MIL-53（A1） with high thermal stability was prepared by a solvothermal method,serving as a support material of cerium doped copper catalyst（Ce-Cu）/MIL-53（A1） material for CO oxidation with high catalytic activity.The catalytic performance between the（CuCe）/MIL-53（A1） and the Cu/MIL-53（A1） catalytic material was compared to understand the catalytic behavior of the catalysts.The catalysts were characterized by thermogravimetric-differential scanning calorimetry（TGDSC）,N2 adsorption- desorption,X-ray diffraction（XRD）,and transmission electron microscopy（TEM）.The characterization results showed that MIL-53（A1） had good stability and high surface areas,the（Ce-Cu）nanoparticles on the MIL-53（A1） support was uniform.Therefore,the heterogeneous catalytic composite materials（Ce-Cu）/MIL-53（A1） catalyst exhibited much higher activity than that of the Cu/MIL- 53（A1） catalyst in CO oxidation test,with 100%conversion at 80 ℃.The results reveal that（Cu-Ce）/MIL-53（A1） is the suitable candidate for achieving low temperature and higher activity CO oxidation catalyst of MOFs.

Structural regulation of single-atom catalysts for enhanced catalytic oxidation performance of volatile organic compounds

The catalytic oxidation of volatile organic compounds(VOCs)is considered a feasible method for VOCs treatment by virtue of its low technical cost,high economic efficiency,and low additionally produced pollutants,which is of important social value.Singleatom catalysts(SACs)with 100%atom utilization and uniform active sites usually have high activity and high product selectivity,and promise a broad range of applications.Precise regulation of the microstructures of SACs by means of defect engineering,interface engineering,and electronic effects can further improve the catalytic performance of VOCs oxidation.In this review,we introduce the mechanisms of VOCs oxidation,and systematically summarize the recent research progress of SACs in catalytic VOCs total oxidation into CO_(2)and H_(2)O,and then discuss the effects of various structural regulation strategies on the catalytic performance.Finally,we summarize the current problems yet to be solved and challenges currently faced in this field,and propose future design and research ideas for SACs in catalytic oxidation of VOCs.

Promotional catalytic activity and reaction mechanism of Ag-modified Ce_(0.6)Zr_(0.4)O_(2) catalyst for catalytic oxidation of ammonia

Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of adsorption-transformationdesorption process were investigated over the Ag-impregnated catalysts for lowtemperature selective catalytic oxidation of ammonia(NH_(3)-SCO).The optimal 5 wt.%Ag/Ce_(0.6)Zr_(0.4)O_(2) catalyst presented good NH_(3)-SCO performancewith>90% NH_(3) conversion at temperature(T)≥250°C and 89% N_(2) selectivity.Despite the irregular block shape and underdeveloped specific surface area(∼60m2/g),the naked and Ag-modified Ce_(0.6)Zr_(0.4)O_(2) solid solution still obtained highly dispersed distribution of surface elements analyzed by scanning electron microscope-energy dispersive spectrometer(SEM-EDS)(mapping),N_(2) adsorptiondesorption test and X-ray diffraction(XRD).H2 temperature programmed reduction(H2-TPR)and X-ray photoelectron spectroscopy(XPS)results indicated that Ag-modification enhanced the mobility and activation of oxygen-species leading to a promotion on CeO_(2) reducibility and synergistic Ag0/Ag+and Ce^(4+)/Ce^(3+)redox cycles.Besides,Ag+/Ag_(2)O clusters could facilitate the formation of surface oxygen vacancies that was beneficial to the adsorption and activation of ammonia.NH3-temperature programmed desorption(NH_(3)-TPD)showed more adsorption-desorption capacity to ammoniawere provided by physical,weakandmedium-strong acid sites.Diffused reflectance infrared Fourier transform spectroscopy(DRIFTS)experiments revealed the activation of ammonia might be the control step of NH3-SCO procedure,during which NH3 dehydrogenation derived from NHx-species and also internal selective catalytic reduction(i-SCR)reactions were proposed.

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

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