Adsorbed Oxygen Species Concentration Research Articles

Mesoporous Si-WO3-supported Pt catalysts with high catalytic performance and excellent water resistance for toluene oxidation

Reducing emissions of volatile organic compounds (VOCs) is an integral part of improving the quality of the atmospheric environment. Catalytic oxidation has become an effective means of treating low and medium concentration VOCs exhausts due to its advantages in terms of removal efficiency, energy saving and environmental protection. Due to the unique inherent properties of supported precious metal catalysts, they show good catalytic efficiency in VOCs emission reduction. In this study, the mesoporous Si-WO3 support was first synthesized by the P123-assisted sol-gel method, and the xPt/Si-WO3 catalysts with the actual loadings (x = 0.19, 0.48, and 0.81 wt%) of Pt nanoparticles (NPs) were then obtained, physicochemical properties of these materials were characterized using a variety of techniques, and their catalytic activities and water resistance for the oxidation of toluene were evaluated. The results showed that Pt NPs with an average particle size of 2.3−3.3 nm were highly dispersed on the mesoporous Si-WO3 support, and the 0.81Pt/Si-WO3 sample exhibited the highest catalytic activity for toluene oxidation at a space velocity of 20,000 mL/(g h) (T50% = 167 °C and T90% = 180 °C; specific reaction rate at 160 °C = 8.54 µmol/(gPt s), turnover frequency (TOFPt) at 160 °C = 1.67 × 10−3 s−1, and apparent activation energy = 45 kJ/mol). The good catalytic performance of 0.81Pt/Si-WO3 was associated with its large surface area, well dispersed Pt NPs, high adsorbed oxygen species concentration, large toluene adsorption capacity, and strong interaction between Pt NPs and mesoporous Si-WO3. The 0.81Pt/Si-WO3 sample possessed excellent water resistance, and the introduction of 5 vol% or 10 vol% water vapor to the reaction system enhanced toluene oxidation since part of water vapor participated in the oxidation of toluene. In addition, the toluene oxidation pathway might obey the sequence of (adsorbed toluene + adsorbed oxygen species) → benzyl alcohol → (benzoic acid and benzaldehyde) → maleic anhydride → (carbon dioxide and water).

Catalytic performance of Nb2O5 modified Ru/CeO2 for dichloromethane oxidation

1 ​wt% Ru/5 ​wt% Nb2O5/CeO2 (RuNbCe) catalyst was synthesized via the incipient wetness impregnation method, and measured for the catalytic oxidation of dichloromethane (DCM). The physicochemical properties of catalysts were determined used various characterization techniques. Compared with 1 ​wt% Ru/CeO2, 5 ​wt% Nb2O5/CeO2, CeO2, 1 ​wt% Ru/xNb2O5/CeO2 (x ​= ​1 ​wt%, 2 ​wt%, and 3 ​wt%) and 1 ​wt% Ru/yMOn/CeO2 (M ​= ​Co, Cr, Fe, Mg, Cu; y ​= ​5 ​wt%), the addition of 5 ​wt% Nb2O5 obviously improved the catalytic performance of 1 ​wt% Ru/CeO2, with the T90% and apparent activation energy (Ea) being 287 oC and 43.5 ​kJ/mol, respectively, and less formation of polychlorinated byproducts at space velocity (SV) ​= ​15,000 ​mL ​g‒1 ​h‒1. The RuNbCe catalyst showed good thermal and hydrothermal stability, as well as HCl-resistance performance. We deduced that the higher oxidation performance of the RuNbCe catalyst may be attributed to the suitable acidic sites, good redox capacity, high surface adsorbed oxygen species concentration, and the strong interaction among Ru, Nb2O5 and CeO2. The RuNbCe catalyst has the potential to be applied for the elimination of chlorinated volatile organic compounds (CVOCs).

Oxygen activity regulation over LaNiO3 perovskites by Ti substitution for chemical looping partial oxidation of methane

The oxygen species in oxygen carriers directly influence the reaction performance in chemical looping processes. This paper describes the relationship between oxygen species and performance in chemical looping partial oxidation of methane (CLPOM) over LaNixTi1-xO3-δ (x = 0, 0.25, 0.5, 0.75 and 1) perovskites. Due to the increase of Ti substitution, the predominate reaction during CLPOM gradually changes from complete oxidation to partial oxidation. Quasi in situ XPS characterization suggests that the relative concentration of nucleophilic lattice oxygen species for partial oxidation increases with Ti substitution, while the relative concentration of electrophilic adsorbed oxygen species for complete oxidation decreases. The moderate Ti substitution for LaNi0.5Ti0.5O3-δ provides the suitable lattice oxygen activity for the methane partial oxidation. Moreover, LaNi0.5Ti0.5O3-δ exhibits high cyclic stability in redox cycles. This work demonstrates that the regulation of oxygen species distribution and activity is feasible to tailor the reaction performance of oxygen carriers in chemical looping processes.

Simple preparation of yolk-shell ZnCr2O4 microspheres and their application to xylene gas sensor

Spinel-type oxides have attracted more and more attention due to their high thermodynamic stability, good catalytic characteristic and flexibly tunable features. Herein, we report the synthesis of yolk-shell ZnCr2O4 microspheres with superior xylene sensing properties by a one-step solvothermal approach. The gas sensing properties of the as-prepared ZnCr2O4 microspheres were investigated. The sensor based on yolk-shell ZnCr2O4 microspheres showed excellent selectivity to xylene having a high response value of 200.7–100 ppm xylene, which was almost 77 times than that of Cr2O3 microspheres at 225 °C. As for the detection limit, the response value of sensor to 0.5 ppm xylene was 1.2. In addition, after 22 days of measurement, it could still keep the response of nearly 200–100 ppm xylene, indicating good long-term stability. The excellent gas sensing performances of sensor to xylene can be ascribed to the yolk-shell architecture with a large specific surface area and the high surface adsorbed oxygen species concentration.

PdPty/V2O5-TiO2: Highly Active Catalysts with Good Moisture- and Sulfur Dioxide-Resistant Performance in Toluene Oxidation

Catalytic performance and moisture and sulfur dioxide resistance are important for a catalyst used for the oxidation of volatile organic compounds (VOCs). Supported noble metals are active for VOC oxidation, but they are easily deactivated by water and sulfur dioxide. Hence, it is highly desired to develop a catalyst with high performance and good moisture and sulfur dioxide resistance in the oxidation of VOCs. In this work, we first adopted the hydrothermal method to synthesize a V2O5-TiO2 composite support, and then employed the polyvinyl alcohol (PVA)-protecting NaBH4 reduction strategy to fabricate xPdPty/V2O5-TiO2 catalysts (x and y are the PdPty loading (0.41, 0.46, and 0.49 wt%) and Pt/Pd molar ratio (2.10, 0.85, and 0.44), respectively; the corresponding catalysts are denoted as 0.46PdPt2.10/V2O5-TiO2, 0.41PdPt0.85/V2O5-TiO2, and 0.49PdPt0.44/V2O5-TiO2). Among all the samples, 0.46PdPt2.10/V2O5-TiO2 exhibited the best catalytic activity for toluene oxidation (T50% = 220 °C and T90% = 245 °C at a space velocity of 40,000 mL/(g h), apparent activation energy (Ea) = 45 kJ/mol), specific reaction rate at 230 °C = 98.6 μmol/(gPt s), and turnover frequency (TOFNoble metal) at 230 °C = 142.2 × 10−3 s−1. The good catalytic performance of 0.46PdPt2.10/V2O5-TiO2 was associated with its well-dispersed PdPt2.10 nanoparticles, high adsorbed oxygen species concentration, good redox ability, large toluene adsorption capacity, and strong interaction between PdPty and V2O5-TiO2. No significant changes in toluene conversion were detected when 5.0 vol% H2O or 50 ppm SO2 was introduced to the reaction system. According to the characterization results, we can realize that vanadium is the main site for SO2 adsorption while PdO is the secondary site for SO2 adsorption, which protects the active Pt site from being poisoned by SO2, thus making the 0.46PdPt2.10/V2O5TiO2 catalyst show good sulfur dioxide resistance.

Catalytic performance and SO2 resistance of zirconia-supported platinum-palladium bimetallic nanoparticles for methane combustion

Methane can induce a serious greenhouse effect, and it is highly required to control its emissions. In this work, we used PdCl2 and H2PtCl6 as noble metal precursors, polyvinyl alcohol as protecting agent, and NaBH4 as reducing agent to synthesize the PtPdx bimetallic nanoparticles (NPs), which were then supported on the surface of zirconia to generate the yPtPdx/ZrO2 (i.e., 0.44PtPd2.20/ZrO2, 0.54PtPd0.90/ZrO2, and 0.61PtPd0.48/ZrO2; x and y are the Pd/Pt molar ratio and PtPdx loading, respectively; x = 0.48–2.20; and y = 0.44–0.61 wt%) catalysts. For comparison purposes, we also prepared the 0.55 wt% Pd/ZrO2 (0.55 Pd/ZrO2) and 0.65 wt% Pt/ZrO2 (0.65Pt/ZrO2) catalysts. It was shown that the PtPdx NPs with an average size of 2.4–3.6 nm were highly dispersed on the ZrO2 support. Among these samples, 0.44PtPd2.20/ZrO2 exhibited the best catalytic activity (T50% = 345 °C and T90% = 408 °C at space velocity = 20,000 mL/(g h); apparent activation energy = 59 kJ/mol; turnover frequency (TOFPd) at 350 °C = 124.1 × 10–3 s−1, and specific reaction rate at 350 °C = 466.6 μmol/(gPd s)). The good performance of 0.44PtPd2.20/ZrO2 was associated with its well dispersed PtPd2.20 NPs, high adsorbed oxygen species concentration, good redox ability, large methane adsorption capacity, and strong interaction between PtPdx and ZrO2. Furthermore, the 0.44PtPd2.20/ZrO2 catalyst also possessed excellent thermal stability and good water- and sulfur dioxide-resistant performance. According to the characterization results, we deduce that SO2 could be preferentially adsorbed at the Pt site in 0.44PtPd2.20/ZrO2 and protected the active phase of PdO from being poisoned by SO2, thus improving its SO2 resistance.

Experimental and density functional theory investigations on the oxidation of typical aromatics over the intermetallic compounds-derived AuMn/meso-Fe2O3 catalysts

Aromatic volatile organic compounds (VOCs) are usually pollutants to the atmosphere environment and human health. In the present work, we first adopted the co-reduction and KIT-6-templating strategies to prepare the AuxMny intermetallic compounds and mesoporous iron oxide (meso-Fe2O3), respectively, and then used the impregnation method to generate the AuxMny/meso-Fe2O3 catalysts. Catalytic performance of these materials was evaluated for benzene, toluene or o-xylene (typical aromatics) oxidation. It is found that the Au5Mn2/meso-Fe2O3 catalyst exhibited the best activity: the temperatures at benzene conversions of 50 and 90 % were 237 and 254 °C at a space velocity of 20,000 mL/(g h), with the TOFAu values and specific reaction rates at 210 and 230 °C being 1.08 and 2.29 s−1, and 6.92 and 11.58 mmol/(gAu s), respectively. Such excellent performance of Au5Mn2/meso-Fe2O3 was related to its well dispersed Au5Mn2 nanoparticles, high adsorbed oxygen species concentration, good low-temperature reducibility, high benzene adsorption capacity, and strong benzene adsorption. The benzene chemisorption mechanism and adsorbed oxygen species could greatly influence the oxidation of benzene. According to the first-principles calculations, we find that benzene adsorption on the surface of Au in Au5Mn2/meso-Fe2O3 was in the form of a π bond, in which the Au could obtain electrons from benzene ring in the presence of benzene adsorption, resulting in a stronger adsorption of benzene and thus increasing the catalytic activity for benzene oxidation. The mechanism of benzene oxidation might take place via the route of benzene → phenol → benzoquinone → maleate (acetate) → carbon dioxide and water.

An investigation on catalytic performance and reaction mechanisms of Fe/OMS-2 for the oxidation of carbon monoxide, ethyl acetate, and toluene

The octahedral molecular sieve (OMS-2)-supported Fe (xFe/OMS-2: x = 1, 3, 5, and 10) catalysts were prepared using the pre-incorporation method. Physicochemical properties of the as-synthesized materials were characterized by means of various techniques, and their catalytic activities for CO, ethyl acetate, and toluene oxidation were evaluated. Among all of the samples, performed the best, with the reaction temperature required to achieve 90% conversion (T90%) being 160°C for CO oxidation, 210°C for ethyl acetate oxidation, and 285°C for toluene oxidation. Such a good catalytic performance of 5Fe/OMS-2 was associated with its high (Mn3+ + Mn2+) content and adsorbed oxygen species concentration, and good low-temperature reducibility and lattice oxygen mobility as well as strong interaction between Fe and OMS-2. In addition, catalytic mechanisms of the oxidation of three pollutants over the 5Fe/OMS-2 catalyst were also studied. It was found that CO, ethyl acetate or toluene was first adsorbed, then the related intermediates were formed, and finally the formed intermediates were completely converted into CO2 and H2O.

An investigation on catalytic performance and reaction mechanism of RuMn/meso-TiO2 derived from RuMn intermetallic compounds for methyl ethyl ketone oxidation

In this work, we first used the oil-phase co-reduction strategy to synthesize the RuxMny (Mn/Ru molar ratio (y/x) = 7 : 20, 21 : 25, and 17 : 10) intermetallic compounds, then used the KIT-6-templeting method to prepare mesoporous titania (meso-TiO2), and finally used the impregnation method to generate the RuxMny/meso-TiO2 (Ru loading = 0.60–0.79 wt%) catalysts. Various techniques were used to measure physicochemical properties of the samples, and their catalytic performance was determined for methyl ethyl ketone (MEK) oxidation. It is found that the RuxMny/meso-TiO2 samples possessed a three-dimensionally ordered mesoporous structure, a surface area of 71–173 m2/g, and a uniform RuxMny particle size of 2.3–2.9 nm. Among all of the samples, Ru25Mn21/meso-TiO2 exhibited the best catalytic performance and good hydrothermal stability: the temperatures at MEK conversions of 10, 50, and 90 % were 131, 226, and 248 °C at a space velocity of 20,000 mL/(g h), with the apparent activation energy, specific reaction rate at 160 °C, and turnover frequency (TOF) at 160 °C being 73 kJ/mol, 41.73 mmol/(gRu s), and 4.20 s−1, respectively. In addition, introduction of 5 vol% moisture to the reaction system exerted a positive effect on catalytic activity of Ru/meso-TiO2 or Ru25Mn21/meso-TiO2 at higher temperatures. Such good performance of the Ru25Mn21/meso-TiO2 sample was related to its well dispersed Ru25Mn21 nanoparticles, high adsorbed oxygen species concentration, active surface lattice oxygen, high MEK adsorption capacity, good redox ability, and strong interaction between Ru25Mn21 and meso-TiO2. We propose that MEK might be oxidized by the adsorbed oxygen and/or surface lattice oxygen species via in turn formation of 2,3-butanedione, acetaldehyde, acetic acid, formaldehyde, and formic acid, all of which were finally converted to water and carbon dioxide.

Oxidative Removal of Volatile Organic Compounds over the Supported Bimetallic Catalysts

Volatile organic compounds (VOCs) and methane are pollutants that are harmful to the atmosphere and human health. It is highly required to control emissions of VOCs. Catalytic oxidation is one of the most effective pathways for the elimination of VOCs, in which the key issue is the development of novel and high-performance catalysts. In this review article, we briefly summarize the preparation strategies, physicochemical properties, catalytic activities, and stability for the oxidative removal of VOCs of the supported bimetallic catalysts that have been investigated by our group and other researchers. The supported bimetallic catalysts include the supported noble bimetal, supported noble metal-transition metal, and supported non-precious bimetal catalysts. It was found that catalytic performance was related to one or several factors, such as specific surface area, pore structure, particle size and dispersion, adsorbed oxygen species concentration, reducibility, lattice oxygen mobility, acidity, reactant activation ability, and/or interaction between bimetals or between metal and support. The stability and ability of anti-poisoning to water, carbon dioxide or chlorine were related to the nature of the bimetal and support in the catalysts. In addition, we also envision the development trend of such a topic in the future work.

AuPd/Co3O4/3DOM MnCo2O4: Highly active catalysts for methane combustion

Three-dimensionally ordered macroporous (3DOM) MnCo2O4-supported Co3O4 and AuPd (xAuPdz/yCo3O4/3DOM MnCo2O4; x = 0.56–1.98 wt%, z = 1.9–2.1, and y = 4.80–24.36 wt%) catalysts were prepared using polymethyl methacrylate (PMMA) microsphere-templating, incipient wetness impregnation, and polyvinyl alcohol (PVA)-protected reduction methods. Physicochemical properties of the materials were characterized by means of numerous techniques, and their catalytic activities were evaluated for methane combustion. It is found that the xAuPdz/yCo3O4/3DOM MnCo2O4 samples with a surface area of 26.5–53.1 m2/g possessed a high-quality 3DOM architecture, in which the AuPd nanoparticles (NPs) with a size of 4.6–5.8 nm were highly dispersed on the surface of the macropore framework. Among all of the samples, 1.98AuPd2.1/18.20Co3O4/3DOM MnCo2O4 exhibited the highest catalytic activity: the T10%, T50%, and T90% (temperatures required for achieving methane conversions of 10, 50, and 90 %, respectively) were 262, 340, and 408 °C at a space velocity of 40,000 mL/(g h). Partial deactivation of the 1.98AuPd2.1/18.20Co3O4/3DOM MnCo2O4 sample due to introduction of water vapor or carbon dioxide was reversible. It is concluded that the good catalytic performance of 1.98AuPd2.1/18.20Co3O4/3DOM MnCo2O4 was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Co3O4 or AuPd2.1 NPs and 3DOM MnCo2O4.

Effect of A-site element on the performance of three-dimensionally ordered macroporous manganese-based perovskite catalyst

Three-dimensionally ordered macroporous manganese-based perovskite catalyst (3DOM AMnO3, A = Ce, La, Ni) were synthesized by PMMA hard-templating and impregnation method. Physicochemical properties of the samples were characterized by means of various techniques including XRD, BET, SEM, TEM, XPS and H2-TPR, and their catalytic activities were evaluated by toluene combustion. It was found that the 3DOM AMnO3 in each of the samples was perovskite in crystal structure, and only the samples possessed a good quality 3DOM architecture with a surface area of 48.8 m2/g. Due to the highest adsorbed oxygen species concentration (Oads/Olatt = 2.330), the best low-temperature reducibility (The low-temperature reduction peaks of 3DOM CeMnO3 catalysts occur at 425 °C) and the strong interaction between CeO2 and MnOx formed during calcination. The 3DOM CeMnO3 sample showed lower apparent activation energy (34.51 kJ·mol−1, SV = 15,000 h−1) and the best catalytic activity for toluene combustion, with the reaction temperatures (T50%, and T90%) required for achieving toluene conversions of 50%, and 90% being 100 °C, 172 °C at SV = 15,000 h−1, respectively.

Effect of transition metal oxide doping on catalytic activity of titania for the oxidation of 1,2-dichloroethane

Transition metal oxides (MOx; M = Cr, Mn, Fe, Ni, Cu)-doped titania solid solution catalysts (10 wt% MOx–TiO2, denoted as 10MOx–TiO2) were prepared by the coprecipitation method. The techniques of XRD, TPR, TPD, XPS, TPSR, and in situ DRIFTS were used to characterize physicochemical properties of the materials, and their catalytic activities were evaluated for the oxidation of 1,2-dichloroethane (1,2-DCE). The introduction of MOx enhanced adsorption and activation of oxygen molecules, mobility of surface lattice oxygen, and low-temperature reducibility. The 10MOx–TiO2 catalysts showed good performance, with 10CrOx–TiO2 exhibiting the highest catalytic activity (reaction rate = 2.35 × 10−7 mol/(gcat s) and apparent activation energy (Ea) =35 kJ/mol at space velocity = 40,000 mL/(g h)) and good resistance to chlorine poisoning, The mechanism of 1,2-DCE oxidation over 10CrOx–TiO2 was also discussed based on the results of TPSR and in situ DRIFTS characterization. It is concluded that strong acidity and redox ability, high adsorbed oxygen species concentration, and strong interaction between TiO2 and CrOx were accountable for the good performance of 10CrOx–TiO2.

Alloying of gold with palladium: An effective strategy to improve catalytic stability and chlorine-tolerance of the 3DOM CeO2-supported catalysts in trichloroethylene combustion

The three-dimensionally ordered macroporous (3DOM) CeO2-supported Au–Pd alloys (xAuPdy/3DOM CeO2, x is the total loading (wt%) of Au and Pd, and y is the Pd/Au molar ratio) were synthesized using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The samples were characterized by a number of analytical techniques, and their catalytic performance was evaluated for the combustion of trichloroethylene (TCE). It is found that the xAuPdy/3DOM CeO2 samples displayed a good-quality 3DOM architecture, and the noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the skeleton surface of 3DOM CeO2. Among all of the samples, 2.85AuPd1.87/3DOM CeO2 exhibited the highest catalytic activity, with the temperature at a TCE conversion of 90% (T90%) being 415 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 2.85AuPd1.87/3DOM CeO2 sample possessed the lowest apparent activation energy (33 kJ/mol), excellent catalytic stability, and good moisture- and chlorine-tolerant behaviors. Alloying of Au with Pd changed the pathway of TCE oxidation and reduced formation of perchloroethylene. We conclude that the excellent catalytic performance for TCE combustion of 2.85AuPd1.87/3DOM CeO2 was associated with the highly dispersed AuPd1.87 alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd1.87 NPs and 3DOM CeO2 as well as the high-quality 3DOM structure and high surface acidity.

Partially embedding Pt nanoparticles in the skeleton of 3DOM Mn2O3: An effective strategy for enhancing catalytic stability in toluene combustion

Polymethyl methacrylate-templating and ethylene glycol reduction methods were adopted to prepare the nanosized Pt catalysts (x wt% Pt/3DOM Mn2O3; x = 0.2–2.3) that were partially embedded in the skeleton of three-dimensionally ordered macroporous (3DOM) Mn2O3. These materials possessed a surface area of 33–36 m2/g, with the Pt NPs (3.6–4.4 nm in size) being well embedded in the skeleton of 3DOM Mn2O3. The 2.3 wt% Pt/3DOM Mn2O3 sample showed the best activity and the lowest apparent activation energy (41 kJ/mol) for toluene combustion, which was related to its high adsorbed oxygen species concentration and good low-temperature reducibility. Compared with 2.0 wt% Pt/3DOM Mn2O3-imp derived from the colloid adsorption method, 2.3 wt% Pt/3DOM Mn2O3 exhibited a better catalytic stability within 60 h of toluene combustion. After calcination at 650 °C for 3 h, the average particle size of Pt nanoparticles (NPs) in 2.3 wt% Pt/3DOM Mn2O3 grew up slightly from 4.3 to 4.9 nm and toluene conversions decreased slightly, while that of Pt NPs in 2.0 wt% Pt/3DOM Mn2O3-imp increased greatly from 4.4 to 13.7 nm and toluene conversions dropped significantly. Effects of H2O, CO2, and SO2 on activity of 2.3 wt% Pt/3DOM Mn2O3 and 2.0 wt% Pt/3DOM Mn2O3-imp were also examined. Partial deactivation induced by H2O or CO2 addition was reversible, whereas that due to SO2 introduction was irreversible. It is concluded that the strong interaction between Pt NPs and 3DOM Mn2O3 was responsible for excellent stability of the partially Pt-embedded 3DOM Mn2O3 sample in toluene combustion.

AgAuPd/meso-Co3O4: High-performance catalysts for methanol oxidation

The meso-Co3O4 and AgxAuyPd/meso-Co3O4 catalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected NaBH4 reduction methods, respectively. Various techniques were used to characterize physicochemical properties of these materials. Catalytic performance of the samples was evaluated for methanol combustion. The cubically crystallized Co3O4 support displayed a three-dimensionally ordered mesoporous structure. The supported noble metal nanoparticles (NPs) possessed a surface area of 115−125 m2/g, with the noble NPs (average size = 2.8−4.5 nm) being uniformly dispersed on the surface of meso-Co3O4. Among all of the samples, 0.68 wt% Ag0.75Au1.14Pd/meso-Co3O4 showed the highest catalytic activity (T50% = 100 °C and T90% = 112 °C at a space velocity of 80000 mL (g−1 h−1). The partial deactivation of the 0.68 wt% Ag0.75Au1.14Pd/meso-Co3O4 sample due to water vapor or carbon dioxide introduction was reversible. It is concluded that the good catalytic performance of 0.68 wt% Ag0.75Au1.14Pd/meso-Co3O4 was associated with its highly dispersed Ag0.75Au1.14Pd alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Ag0.75Au1.14Pd alloy NPs and meso-Co3O4.

Three-dimensionally ordered macroporous Cr2O3−CeO2: High-performance catalysts for the oxidative removal of trichloroethylene

Abstract Three-dimensionally ordered macroporous (3DOM) CeO2, 3DOM Cr2O3, 3DOM xCr2O3−CeO2 (x (the weight percentage of Cr2O3) = 3.5, 5.5, and 8.0 wt%), and 5.5 wt% Cr2O3/3DOM CeO2 samples were prepared using the polymethyl methacrylate (PMMA)-templating and incipient wetness impregnation methods, respectively. A number of techniques were used to characterize physicochemical properties of the materials, and their catalytic activities were evaluated for the oxidation of trichloroethylene (TCE). These samples possessed a good-quality 3DOM structure and a surface area of 35−47 m2/g. The 3DOM 5.5Cr2O3−CeO2 sample performed the best (the temperature at TCE conversion = 90% = 255 °C at a space velocity of 20,000 mL/(g h)). Effects of water vapor and carbon dioxide on activity of the 5.5Cr2O3−CeO2 sample were also examined. It is observed that partial deactivation induced by H2O introduction of the 5.5Cr2O3−CeO2 sample was reversible, while that induced by CO2 addition was irreversible. Based on the activity data and characterization results, it is concluded that the good catalytic activity and thermal stability of 3DOM 5.5Cr2O3−CeO2 was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Cr2O3 and CeO2. We believe that the 3DOM 5.5Cr2O3−CeO2 catalyst is promising in the application for oxidative removal of chlorinated volatile organic compounds.

Effect of Crystal Phase of MnO2 with Similar Nanorod‐Shaped Morphology on the Catalytic Performance of Benzene Combustion

AbstractFour manganese oxides with different crystal structures in the similar nanorod‐shaped morphology were synthesized and investigated for the catalytic combustion of benzene. The physicochemical properties of the materials were characterized by N2 physisorption‐desorption, transmission electron microscope (TEM), X‐ray photoelectron spectroscopy (XPS), Raman spectra, O2 temperature programmed desorption (O2‐TPD) and temperature programmed surface reaction (TPSR). The catalytic activities on benzene combustion over various manganese oxides decreased in the order: γ‐MnO2 > β‐MnO2 > α‐MnO2 > δ‐MnO2. The activation energy of benzene combustion over γ‐MnO2 (67.4 kJ/mol) was lower than that over α‐MnO2 (69.2 kJ/mol), β‐MnO2 (79.1 kJ/mol) and δ‐MnO2 (85.2 kJ/mol). The TPSR results with or without gaseous oxygen revealed that the reaction pathway was occurred via MVK mechanism. The surface adsorbed oxygen species concentration and low temperature O2 desorption of these manganese oxides, determined by XPS and O2‐TPD, decreased in the order of γ‐MnO2 > β‐MnO2 > α‐MnO2 > δ‐MnO2, are in good agreement with the sequence of their catalytic performance on benzene combustion. It is concluded that higher surface adsorbed oxygen species ratio and better low temperature O2 desorption were crucial to the superior catalytic performance of the α‐MnO2, β‐MnO2, γ‐MnO2 and δ‐MnO2 materials.

AuPd/3DOM TiO2 Catalysts: Good Activity and Stability for the Oxidation of Trichloroethylene

Three-dimensionally ordered macroporous (3DOM) TiO2-supported AuPd alloy (xAuyPd/3DOM TiO2 (x = 0.87–0.91 wt%; y = 0.51–1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials possessed a good-quality 3DOM structure and a surface area of 49–53 m2/g. The noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the surface of 3DOM TiO2. The 0.91Au0.51Pd/3DOM TiO2 sample showed the highest catalytic activity with the temperature at a TCE conversion of 90% being 400 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 0.91Au0.51Pd/3DOM TiO2 sample possessed better catalytic stability and moisture-resistant ability than the supported Au or Pd sample. The partial deactivation induced by H2O introduction of 0.91Au0.51Pd/3DOM TiO2 was reversible, while that induced by CO2 addition was irreversible. No significant influence on TCE conversion was observed after introduction of 100 ppm HCl to the reaction system over 0.91Au0.51Pd/3DOM TiO2. The lowest apparent activation energy (51.7 kJ/mol) was obtained over the 0.91Au0.51Pd/3DOM TiO2 sample. The doping of Au to Pd changed the TCE oxidation pathway, thus reducing formation of perchloroethylene. It is concluded that the high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd NPs and 3DOM TiO2 as well as more amount of strong acid sites were responsible for the good catalytic activity, stability, and water- and HCl-resistant ability of 0.91Au0.51Pd/3DOM TiO2. We believe that 0.91Au0.51Pd/3DOM TiO2 may be a promising catalyst for the oxidative elimination of chlorine-containing volatile organics.

PtxCo/meso-MnOy: Highly efficient catalysts for low-temperature methanol combustion

The KIT-6-templating and polyvinyl alcohol-protected NaBH4 reduction methods were adopted to prepare the mesoporous manganese oxide (meso-MnOy) and its supported Co, Pt, and PtxCo catalysts, respectively. Numerous techniques were used to characterize the physicochemical properties of the materials. Catalytic performance of the samples was evaluated for methanol combustion. All of the samples possessed a three-dimensionally ordered mesoporous structure and a surface area of 94–110 m2/g. The Co, Pt, and PtxCo nanoparticles (NPs) with an average size of 2.2–3.0 nm were uniformly dispersed on the surface of meso-MnOy. The 0.70 wt% Pt2.42Co/meso-MnOy sample performed the best: the T50% and T90% (temperatures required for achieving methanol conversions of 50 and 90%, respectively) were 50 and 86 °C at a space velocity of 80,000 mL/(g h). The partial deactivation of the 0.70Pt2.42Co/meso-MnOy sample due to water vapor or carbon dioxide introduction was reversible. It is concluded that the excellent catalytic activity of 0.70 wt% Pt2.42Co/meso-MnOy was associated with its highly dispersed Pt2.42Co alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Pt2.42Co alloy NPs and meso-MnOy.