Surface Active Oxygen Species Research Articles

Effect of CeO2 nanoparticle sizes on catalytic performances of sulfated CeO2/Al2O3 catalyst in NH3-SCR reaction

The sulfated CeO2/Al2O3 catalysts with different sizes of CeO2 nanoparticles were prepared by using pure H2O or acetic acid solution as impregnation solvent, and the influence of sizes of CeO2 nanoparticles on the catalytic performances of the sulfated CeO2/Al2O3 catalyst was studied. The catalytic performance tests show that the sulfated CeO2/Al2O3 catalyst using acetic acid solution as impregnation solvent has better catalytic activity and the resistance to K+ poisoning than the sulfated CeO2/Al2O3 catalyst using pure H2O as impregnation solvent. The excellent catalytic performances can be ascribed to the smaller sizes of CeO2 nanoparticles in CeO2/Al2O3 catalyst using acetic acid solution, which results in larger amount of adsorbed sulfate species, surface acid sites, surface active oxygen species and excellent redox property. These features are helpful for improving the catalytic performances of sulfated CeO2/Al2O3 catalyst using smaller amount of CeO2 to cut the costs.

Desilication tuning of In/Hβ catalysts for sulfur- and steam-resistant CH4-SCR of NO

Mesoporous In/Hβ-X series catalysts were prepared by desilication method with tetrapropylammonium hydroxide (TPAOH) and indium incorporation for selective catalytic reduction of NO with methane (CH4-SCR). The post desilication treatment conditions for preparing In/Hβ-X were optimized. Etching time is the most important desilication parameter influencing the resulting CH4-SCR performance of the catalyst. The In/Hβ-3 sample which was etched for 3 h presents the highest NOx conversion, 22% higher than In/H-Beta counterparts using commercial microporous beta. Obvious analysis reveals that besides generating mesopores, controlled desilication can modulate the proportion of InO+ active sites and surface oxygen species, allowing more active sites to be exposed.

Catalytic ozonation of toluene and dichloromethane mixture at low temperatures over modified MnOx-based catalyst

Catalytic ozonation is an efficient method for VOCs abatement at low temperatures, in which the rational design of highly active heterogeneous catalysts constitutes the most significant step. In this study, Al2O3 was first optimized by loading MnOx. And then K was used for modifying MnOx/Al2O3 catalyst, which exhibited 2.4 × 10−3 mol∙g−1∙s−1 oxidation rate for dichloromethane and toluene oxidation with ca. 0.89 ppm ozone detected at 80 °C. That could be directly applied for removing toluene and dichloromethane mixture or coupled with other treatment technologies (such as biological purification). Besides, appropriate K doping could increase the amount of reactive surface oxygen species and the ratio of Mn2+, hence contributing to an enhanced oxidation ability. By contrast, an excess K doping inevitably lowered the activity of active surface oxygen species and interfered with the transformation of Mn3+ to Mn2+, which resulted in a weakened oxidative ability and thus a decreased catalytic activity. Finally, the reaction mechanisms over 0.1 K-MnOx/Al2O3 were tried to be demonstrated that the degradation of toluene mainly followed the pathway of toluene – phenylcarbinol – benzaldehyde – benzoic acid – phenyl group – small-molecule species and/or CO2 while the route of dichloromethane – methanol – formaldehyde – formic acid – small-molecule species and/or CO2 explained the catalytic oxidation of dichloromethane. All of these findings may facilitate the design of novel heterogeneous catalysts for VOCs oxidation and progress the development of catalytic ozonation for toluene and dichloromethane abatement.

Tailoring oxygen vacancies and active surface oxygen species in CrOx hierarchical strawberry-type three-dimensional (3D) micro-spindle catalysts for total catalytic oxidation of VOCs

Developing efficient and stable non-noble metal catalysts for the catalytic oxidation of volatile organic compounds (VOCs) has always been key for controlling air pollution.

Bismuth phosphate nanoparticle catalyst for direct oxidation of methane into formaldehyde

Monoclinic BiPO4 nanoparticles selectively gave HCHO for the direct oxidation of CH4 thorough the possible involvement of surface active oxygen species on BiPO4 in the activation of CH4.

Investigation of in Situ Co-assembled Sr(Co,Zr)O3−δ-Based Perovskite Nanocomposite Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Exploring cathode materials with fast oxygen reduction reaction (ORR) kinetics is crucial to intermediate-temperature solid oxide fuel cells (SOFCs). Herein, a highly active perovskite nanocomposite with a nominal composition of SrCo0.8Zr0.2O3−δ is developed. The two perovskite phases of cubic SrZr0.8Co0.2O3−δ (SZC, Pm3̅m, 30 wt %) and hexagonal SrCo0.9Zr0.1O3−δ (SCZ, R3̅cH, 70 wt %) can be in situ co-assembled at the nanoscale for well-connected nanoparticles (50–100 nm) and congenital compatibility. The SZC–SCZ nanocomposite can exhibit the active surface oxygen species and a matchable thermal expansion coefficient (15.3 × 10–6 K–1) with Ce0.8Gd0.2O1.9 (13.5 × 10–6 K–1) electrolyte. When applied to the anode-supported SOFC, SZC–SCZ nanocomposite cathode cell shows superior power densities of 1.48–0.41 W cm–2 at 750–550 °C to single cubic SZC cathode cell (0.24–0.06 W cm–2) and typical hexagonal SrCoO3−δ cathode cell (1.25–0.32 W cm–2). The distribution of relaxation times analysis reveals that the oxygen adsorption and dissociation process of SZC–SCZ nanocomposite cathode is significantly enhanced, of which the polarization resistances (0.07–0.22 Ω cm2) are 0.70–0.43 times those of SrCoO3−δ cathode. This benefits from the nanostructure for an extensive heterointerface and surface, and the synergistic interaction of components can contribute to enhancing oxygen catalysis. Thus, this work explores a promising SZC–SCZ nanocomposite cathode for enhancing ORR activity and cell performance at lower operating temperatures.

Catalytic performance and mechanism of bismuth molybdate nanosheets decorated with platinum nanoparticles for formaldehyde decomposition at room temperature

Catalytic oxidation at room temperature is considered as a promising strategy for removal of formaldehyde (HCHO), a widely occurring indoor air pollutant. A series of Bi2MoO6 nanosheets were prepared via one-step hydrothermal synthesis in this study, followed by decoration with Pt nanoparticles (NPs). The catalyst with Bi2MoO6 support prepared at 180 °C exhibited high and stable activity in catalytic oxidation of HCHO at room temperature. The excellent catalytic performance was attributed to its large specific area and pore volume, high level of surface active oxygen species, high content of metallic Pt NPs, and abundant oxygen vacancies. The good synergy and interaction between Pt and Bi2MoO6 promoted electron transfer, and facilitated the adsorption and oxidation of HCHO. The electronic interaction between Pt NPs and Bi2MoO6 accelerated the activation of oxygen species due to weakening of the surface BiO or MoO bonds adjacent to Pt NPs. Infrared spectra indicated that dioxymethylene and formate species were the main intermediates of HCHO oxidation. Density functional theory calculations showed that the dehydrogenation of HCO2, with an energy barrier of 282.1 kJ/mol, was the rate-determining step in catalytic oxidation process. This study provides new insights on the construction of high-efficiency catalysts for indoor formaldehyde removal.

Ni-Mn spinel aerogel catalysts with adsorption induced superior activity for Low-Temperature toluene oxidation

The development of a highly efficient oxide catalyst is crucial for thermal and environmental catalytic reactions. Herein, a facile and eco-friendly strategy is developed to synthesize a series of Au-modified hollow Ni–Mn spinel nanospheres decorated on graphene aerogels (GAs) (termed Auy-hNixMn3−x/GAz) composite catalysts for deep catalytic oxidation of Volatile organic compounds (VOCs). The introduction of hollow structure leads to a larger specific surface area and more accessible active sites. The subsequent cooperation of Au further strengthens the low-temperature reducibility along with more active surface oxygen species. After being embedded into the graphene network, the composite catalyst shows an improvement in electron transfer and accessibility to active metal sites. The adsorption capacity of the catalyst for toluene is greatly improved by the above steps, thus facilitating the catalytic performance. The resulting Au1-hNi1Mn2/GA0.5 composite catalyst exhibits optical activity for VOCs removal, reaching 100 % toluene and benzene (500 ppm) oxidation at 155 °C and 148 °C, respectively. Meanwhile, the catalyst shows extraordinary catalytic stability, selectivity, moisture tolerance and compressibility making it a promising catalyst for industrial thermal catalysis. Moreover, an in situ DRIFTS study is carried out for the exploration of the reaction pathway and a modified Mars van Krevelen (MVK) catalytic mechanism was proposed as well.

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

Porous cryptomelane-type octahedral molecular sieve (OMS-2) with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds (VOC) catalytic elimination. However, complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability. Here, a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the physicochemical properties of which were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Brunauer–Emmett–Teller (BET) method, X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction of H2 (H2-TPR), Raman, In situ diffused reflectance infrared Fourier transform spectra (DRIFTS), and density functional theory (DFT) calculations. Results show that the total conversion of toluene can be achieved at 207 °C over PdCe2 with apparent activation energy as low as 62.6 kJ/mol. The strong synergistic effect between Pd and Ce remarkably boosts the catalytic activity of OMS-2, attributed to the abundant Mn3+–O bands and active surface oxygen species. DFT results reveal that oxygen vacancy can be formed over PdCe2 much easily than that of Pd/OMS-2 and Ce/OMS-2 with the oxygen vacancy formation energy of 2.42, 2.83 and 2.68 eV, respectively. Simply increasing the Pd content cannot promote the catalytic activity although PdO is a critical active center in toluene oxidation. Oxygen vacancy attributed to the integrative effect of Pd, Ce and Mn species plays a prominent role over prepared catalysts in toluene activation process. The findings reported in this work showed new insights into the designing of highly efficient OMS-2 catalysts for VOC deep oxidation by tuning oxygen vacancy concentration.

Vanadium doped OMS-2 catalysts for one-pot synthesis of imine from benzyl alcohol and aniline: Effects of vanadium content and precursor

A series of vanadium doped cryptomelane-type manganese oxide (V-OMS-2) catalysts were prepared by a simple, low-cost reflux method, and investigated for one-pot imine synthesis from oxidative coupling of benzyl alcohol and aniline with air. The physicochemical properties of the V-OMS-2 catalysts were characterized by various techniques including XRD, BET, SEM, TEM, XPS, H2-TPR and NH3-TPD. It was found that the surface area, Lewis acid sites, the amount of Mn3+ component and active surface oxygen species were much improved with vanadium doping. Consequently, the activity of V-OMS-2 catalyst for oxidative coupling of benzyl alcohol and aniline to imine was enhanced. The highest conversion and the imine yield were obtained over the 3 mol% V-OMS-2 catalyst, being ∼99% and 92%, respectively. Higher vanadium doping (≥ 6 mol%), however, hindered the preservation of OMS-2 crystal structure, leading to a drop in the catalytic performance. The high specific surface area was suggested to be the key contributor to the high catalytic activity of 3% V-OMS-2(1) catalyst. Among the vanadium precursors studied, the catalyst prepared with vanadium pentoxide exhibited a much higher catalytic activity, which can be attributed to its larger surface area, unique mesoporous structure, increased Lewis acid sites and more readily available surface oxygen species. In addition, the stability and recyclability of the catalyst were also studied, and the reaction mechanism was discussed.

Pt/NiCo2O4 nanowire arrays on Ni foam as catalysts for efficient formaldehyde oxidation at room temperature

Catalytic oxidation of formaldehyde (HCHO) at room temperature is a low-cost and efficient solution for indoor HCHO removal. In this work, NiCo2O4 nanowires were in-situ synthesized on nickel foam (NF) by a simple hydrothermal reaction and then decorated with platinum nanoparticles (NPs). The Pt/NiCo2O4-NF catalyst exhibited excellent HCHO oxidation capacity at ambient temperature, realizing a conversion rate of 90 % within 60 min. The nickel foam substrate prevents the aggregation of NiCo2O4 nanowire arrays. It also enables the growth of large-area and aligned nanowires, contributing to the uniform dispersion of Pt NPs. Moreover, due to the unique redox property and high reactivity of NiCo2O4, numerous surface oxygen vacancies and active oxygen species are generated together with Pt by NaBH4 reduction, which is beneficial to the adsorption and oxidation of HCHO. Moreover, the hierarchical macro-/mesoporous structure of Pt/NiCo2O4-NF facilitates the diffusion of gaseous reactants and provides easily accessible active sites. In contrast with nanosized catalysts, the three-dimensional (3D) Pt/NiCo2O4-NF catalyst possesses high machinability and practicability. This work may shed light on the fabrication of 3D hierarchical catalysts for oxidative HCHO removal and indoor air purification.

Effects of Nb-modified CeVO4 to form surface Ce-O-Nb bonds on improving low-temperature NH3-SCR deNOx activity and resistance to SO2 & H2O

A series of novel ternary CeVO4 modified with different Nb contents (CeNbVO) catalysts were synthesized via alkali-assisted hydrothermal method, and applied for selective catalytic reduction (SCR) of NOx with NH3. The as-prepared CeNbVO catalysts show enhanced NH3-SCR performance compared with the CeVO catalyst. Especially, the optimal CeNbVO-2 with appropriate Nb amount displays the superior NH3-SCR activity with above 90 % NO conversion in the range of 210–420 °C with 5 %vol·H2O and excellent resistance to H2O/SO2. Effects of Nb-modified CeVO4 to form surface Ce-O-Nb bonds on improving low-temperature NH3-SCR activity and resistance to SO2 & H2O were investigated by using various characterization methods, including XRD, Raman spectroscopy, N2 physical adsorption, TEM, H2-TPR, NH3-TPD, O2-TPD, NO-TPD, XPS, kinetic tests and in-situ DRIFTS. Different phases can be obtained with the different Nb amount doping, leading to different SCR activity. The pure CeVO4 phase with the short-range ordered Nbn+–O2–-Cen+ bond is formed by adding a small amount of Nb in CeNbVO-2. The superior catalytic performance of CeNbVO-2 can be ascribed to its improved acidity and suitable oxidation ability, which may counteract the negative effects of nonselective NH3 oxidation to N2O. It is found that the formation of Nbn+–O2–-Cen+ bonds can significantly increase the surface active oxygen species and oxygen vacancy of the catalyst. Additionally, the NH3-SCR reaction mechanism is revealed using in-situ DRIFTS and kinetic studies.

Boosting propene oxidation activity over LaFeO3 perovskite catalysts by cobalt substitution

To develop robust and cost-effective catalysts for propene total oxidation, LaFe1−xCoxO3 (x = 0, 0.1, 0.2, 0.3, 1) perovskites were prepared via a citrate sol-gel method. XRD, FTIR and Raman analyses suggested that after cobalt substitution, the LaFeO3 structure was well maintained, whereas abundant lattice distortions were generated accompanied by weaker Fe−O bond. H2-TPR and O2-TPD results demonstrated that cobalt incorporation led to better reducibility and higher oxygen mobility of the oxides. The propene oxidation activity of the catalysts was found to increase with the cobalt content, which correlated well with the amount of surface-active oxygen species. The optimal catalyst LaFe0.8Co0.2O3 presented comparable activity to LaCoO3 at much lower cost. Moreover, it showed excellent cyclability (6 cycles) and stability (35 h), decent performance at high space velocity (24,0000 mL g–1 h–1) or in the presence of 5 vol% water, thereby being a promising candidate for industrial application.

Effects of the metal ionic radius at lattice site on surface active oxygen and reducibility over doped mesoporous ZSM-5 for catalytic oxidation VOC

Heteroatomic mesoporous ZSM-5 (Zeolite Socony Mobil–5) as an important catalyst is widely applied in catalytic field, however, its catalytic performance in VOCs oxidation is not clear. Particularly, the effects of the metal ionic radius at lattice site on surface active oxygen and reducibility of ZSM-5 are confused. Herein, Cu-, Mn-, Cr- and Co-doped mesoporous ZSM-5 were synthesized by a hydrothermal method to investigate the effects and altered mechanisms for hexane oxidation via the catalysts containing transition metals with different ionic radii at lattice sites in mesoporous ZSM-5, and the physical/chemical characteristics of all the catalysts were characterized. The results show that surface active oxygen species and low-temperature reducibility as critical factors in hexane oxidation are relevant to the transition metal ion radius. And, moderate-length ionic radius can significantly facilitate the increase in the amount and transfer capacity of the surface reactive oxygen species and the reducibility of catalysts, which exhibits a typical volcano-type curve relationship. Among the prepared catalysts, Cu-HZ (tetra-coordination Cu2+ radius: 0.57 Å), which possesses the largest concentration of superficial lattice oxygen, the highest reducibility and an adequate degree and strength for surface acidity, exhibits the highest catalytic activity, the highest CO2 yield and selectivity. Additionally, compared with the supported mesoporous ZSM-5, the reaction mechanism of hexane oxidation over doped mesoporous ZSM-5 can be intensified by the synergistic effects between the lattice transition metal atom as the acidic adsorption site and the surface reactive oxygen generated by lattice doping of transition metal. We believe that this work can provide new insights into the design of catalysts for VOC degradation.

Recycle of waste activated coke as an efficient sorbent for Hg0 removal from coal-fired flue gas

The desulfurized activated coke was recycled through thermal regeneration to recover Hg0 from coal-fired flue gas. And the thermal treated activated coke was also prepared for comparison. BET, acid-base titration, XPS and O2-TPD characterizations were performed to identify the structural and chemical properties. Although possessing decreased BET surface area and enlarged pore diameter after thermal treatment, AC-400 exhibited the enhanced Hg0 removal performance due to the generation of oxygen functional groups, while the treatment at 900 °C resulted in the decomposition of surface active oxygen species. Besides, not only the strengthened promotion on the formation of carbonyl and ester groups, but also the deposition of SO42− during regeneration should be responsible for the superior activity of regenerated desulfurized activated coke (RAC) for Hg0 removal. Besides, O2 addition could weaken the competition between NO/SO2 and Hg0, and facilitate the formation of Hg(NO3)2/HgSO4. In combination with Hg-TPD, the specific surface area was in closely correlation with the physisorption of Hg0 on activated coke, and the chemisorption, as the predominant mechanism, of Hg0 mainly depended on the surface active oxygen species. Moreover, when reacted at 60 °C, the Hg0 adsorption priority on RAC was as follows: ester ≥ carbonyl ≥ SO42− ≥ physisorption, and the carbonyl was the leading active sites for mercury adsorption.

Experimental and theoretical analysis of elemental mercury removal from syngas over Fe-Ti spinel

A magnetic Fe-Ti spinel sorbent was synthesized by the co-precipitation method and applied to remove gaseous Hg0 from syngas. A superior Hg0 removal performance was achieved in the temperature range of 120–180 °C, and the highest an average removal efficiency of was approximately 95% at 150 °C under simulated syngas. H2S was adsorbed on the Fe-Ti spinel surface，which generated active sulfur species, and enhanced the Hg0 removal efficiency significantly. CO, H2 and H2O variably suppressed the Hg0 removal performance. H2S-pretreatment, X-ray photoelectron spectroscopy (XPS) and Hg0-temperature programmed desorption (Hg0-TPD) results demonstrated that Hg0 reacted with H2S over Fe-Ti spinel followed the Eley-Rideal mechanism, in which gas-phase Hg0 reacted with the active surface sulfur species generated from H2S oxidation and formed surface-bonded HgS. The surface Fe3+ and surface-active oxygen species were involved in the H2S and Hg0 adsorption and transformation process. Stability and regeneration cycling experiments indicated that Fe-Ti spinel exhibited excellent stability for Hg removal and great regeneration ability. Density functional theory (DFT) calculations showed that H2S underwent strong chemisorption on the Fe-Ti spinel surface with an adsorption energy of −116.988 kJ/mol, and then H2S further dissociated on the sorbent surface to generate active sulfur species, which reacted strongly with gas-phase Hg0 to form HgS.

Performance, Reaction Pathway, and Pretreatment of Au Catalyst Precursor in H2/O2 Atmosphere for the Epoxidation of Propylene

Gas-phase epoxidation of propylene in the copresence of H2 and O2 was performed over the catalyst of Au on as-synthesized TS-1 that contained a small amount of anatase TiO2. The catalytic performance was studied by washing or nonwashing the catalyst precursor to modulate the content of purity (K, Cl) and then calcining the samples in O2 or H2 prior to reaction. The results show that the catalytic performance of Au/TS-1 can be improved without washing (more K+ and Au maintained) and O2 pretreatment. It was found that the calcination in O2 was able to maintain more metallic Au and form more surface-active oxygen species and thus providing a better yield of propylene oxide with the assistance of potassium. Interestingly, more acrolein can be produced over the catalysts with respect to the in situ calcination in O2 than that in H2 when the feed only contained 10% O2 and 10% propylene in argon, while there was no formation of propylene oxide. On the other hand, the catalyst precursor calcined in H2 prefers the formation of successive oxygenates of PO.

Strengthen Air Oxidation of Refractory Humic Acid Using Reductively Etched Nickel-Cobalt Spinel Catalyst

Nickel-cobalt spinel catalyst (NCO) is a promising catalyst for air oxidation of humic acid, which is a typical natural refractory organic matter and a precursor of toxic disinfection by-products. In this study, reductive etchers, NaBH4 or Na2SO3, were used to adjust the NCO surface structure to increase the performance. The modified catalyst (NCO-R) was characterized, and the relationship between its intrinsic properties and catalytic paths was discovered. The results of O2-temperature programmed desorption, NH3-temperature programmed desorption, and X-ray photoelectron spectroscopy (XPS) demonstrated that reductant etching introduced oxygen vacancies to the surface of NCO and increased active surface oxygen species and surface acidity. In addition, the modification did not change the raw hollow sphere structure of NCO. The crystallinity and specific surface area of NCO-R increased, and average pore size of NCO-R decreased. XPS results showed that the ratio of Co3+/Co2+ in NCO-R decreased compared with NCO, while the ratio of Ni3+/Ni2+ increased. The results of H2-temperature programmed reduction showed that the H2 reduction ability of NCO-R was stronger. Due to these changes in chemical and physical properties, NCO-R exhibited much better catalytic performance than NCO. In the catalytic air oxidation of humic acid at 25 °C, the total organic carbon (TOC) removal rate increased significantly from 44.4% using NCO to 77.0% using NCO-R. TOC concentration of humic acid decreased by 90.0% after 12 h in the catalytic air oxidation using NCO-R at 90 °C.

Flower-like Co3O4 Catalysts for Efficient Catalytic Oxidation of Multi-Pollutants from Diesel Exhaust

Nowadays, the oxidation activity at the low-temperature regime for Co3O4 catalysts needs to be improved to meet the stringent regulation of multi-pollutant diesel exhaust. Herein, nanoflower-like Co3O4 diesel oxide catalysts (DOCs) were fabricated with the addition of a low-content Pt to trigger better catalytic activities for oxidizing multi-pollutants (CO, C3H6, and NO) emissions by taking advantage of the strong-metal supporting interaction. Compared to the conventional DOCs based on Pt/Al2O3, the as-synthesized Pt/Co3O4 catalysts not only exhibited better multi-pollutants oxidation activities at the low temperature but also obtained better resistance toward NO inhibition. Moreover, Pt/Co3O4 catalysts showed exceptional hydrothermal durability throughout long-term tests in the presence of water vapor. According to the XPS and H2-TPR results, Pt promoted low-temperature catalytic activity by increasing the active surface oxygen species and reducibility due to the robust synergistic interaction between metallic Pt and supporting Co3O4. Meanwhile, TGA curves confirmed the Pt atoms that facilitated the desorption of surface-active oxygen and hydroxyl radicals in a low-temperature regime. Furthermore, instead of probing the intermediates during CO and C3H6 oxidation for Pt/Co3O4 catalysts, which included carbonates, formate, and acetate species, in situ DRIFTs experiments also revealed C3H6 oxidation mainly took place over metallic Pt sites.

Ag-modified SmMn2O5 catalysts for CO and C3H8 oxidation

A series of Sm-Mn oxides (SmMnO3, SmMn2O5 and Sm0.9Ag0.1Mn2O5) of perovskite-type and mullite crystal phases were synthesized for the catalytic oxidation of CO and C3H8. The Sm0.9Ag0.1Mn2O5 composition showed the highest catalytic activity among the series of solids, especially for the CO oxidation to CO2 with T50 and T90 values of 60 and 95 °C, respectively. The catalysts were characterized by powder XRD, Raman, BET, XPS, and H2-TPR. It was found that the catalytic performance of the solids was correlated well with their redox properties. Synergetic effects between Ag-related species and the mullite phase resulted in more active surface oxygen species and remarkably lowered the reduction temperature of the Sm0.9Ag0.1Mn2O5 solid.