Pd/H-ZSM-5 catalysts could completely catalyze CH4 to CO2 at as low as 320 °C, while there is no detectable catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the theoretical and experimental results prove that surface acidic sites could facilitate the formation of active metal species as the anchoring sites, which could further modify the electronic and coordination structure of metal species. PdOx interacting with the surface Brönsted acid sites of H-ZSM-5 could exhibit Lewis acidity and lower oxidation states, as proven by the XPS, XPS valence band, CO-DRIFTS, pyridine FT-IR, and NH3-TPD data. Density functional theory calculations suggest PdOx groups to be the active sites for methane combustion, in the form of [AlO2]Pd(OH)-ZSM-5. The stronger Lewis acidity of coordinatively unsaturated Pd and the stronger basicity of oxygen from anchored PdOx species are two key characteristics of the active sites ([AlO2]Pd(OH)-ZSM-5) for methane combustion. As a result, the PdOx species anchored by Brønsted acid sites of H-ZSM-5 exhibit high performance for catalytic combustion of CH4 over Pd/H-ZSM-5 catalysts.Keywords: H-ZSM-5; Lewis acidity; methane combustion; Pd; surface acidity;

Potassium-doped Co3O4, prepared via the sol–gel method, was pretreated by water washing and subsequently the fresh, washed catalysts were compared with pure Co3O4 in order to investigate the existing states of potassium species and their influence on the activities for NO and soot oxidation. The samples were characterized by N2 adsorption–desorption, XRD, FT-IR, NOx-TPD, CO2-TPD, O2-TPD and XPS. It was found that two types of K species existed in K-Co3O4, i.e., the “free” K and the “stable” K. The “free” K species, which were present as carbonates and nitrates with high mobility, could improve the contact state of catalyst-soot and thus significantly accelerate soot oxidation, but they also greatly covered the active surface of Co3O4 and were adverse for NO oxidation. The “stable” K species, which interacted strongly with Co3O4 and acted as electronic and structural modifiers, facilitated the formation of O−/O2− species and oxygen vacancies, exposed more surface Co3+ sites and increased the amount of the medium/strong basic sites, and as a result, they enhanced the intrinsic activities of Co3O4 for soot and NO oxidation. Both K species improved the NOx storage capacities of Co3O4, and the NOx species adsorbed on medium/strong basic sites with appropriate stability, caused by the effect of the “stable” K, were more beneficial for soot oxidation than those adsorbed on “free” K with high stability.

The catalytic wet air oxidation of aniline over Ru catalysts supported on modified TiO2 (TiO2, Ti0.9Ce0.1O2, Ti0.9Zr0.1O2) is investigated. A series of characterization techniques are conducted to determine the relationship between the physico-chemical properties and the catalytic performance. As a result of the good metal dispersion and large number of surface oxygen species, the Ru/Ti0.9Zr0.1O2 catalyst presents the best catalytic activity among the tested samples. The effects of the operating conditions on the reaction are investigated and the optimal reaction conditions are determined. Based on the relationship between the by-products concentration and the reaction time, the reaction path for the catalytic oxidation of aniline is established. Carbonaceous deposits on the surface of the support are known to be the main reason for catalyst deactivation. The catalysts maintain a constant activity even after three consecutive cycles.Ruthenium supported on the surface of Ti0.9Zr0.1O2 shows high catalytic activity and high stability for catalytic wet oxidation of aniline resulting from homogenous metal dispersion and higher surface active oxygen content.Download high-res image (119KB)Download full-size image

•Doping of Bi2O3 enhances the activity and stability of Co3O4 for soot oxidation.•Bi2O3 doping improves the oxygen vacancy formation and lattice oxygen reactivity.•The channels of oxygen activation are extended over Bi2O3-Co3O4.•Bi2O3-Co3O4 can work efficiently under condition containing H2O and SO2.Bi2O3-Co3O4 catalysts were prepared by sol-gel method and tested for soot oxidation by O2. The composite oxides showed excellent activity under both tight and loose contact when compared with individual Co3O4 or Bi2O3, and the maximum activity was obtained over catalyst with Bi/Co molar ratio of 0.2. The samples were characterized by means of XRD, N2 adsorption, FE-SEM, XPS, FT-IR, C-TPR and O2-TPD. It was found that Bi2O3 with low melting point deposited on Co3O4 surface could not only promote the contact state between soot and catalyst, but also produce more oxygen species with high mobility and reactivity at Bi-Co interface layer. Oxygen activation channel and reaction pathway were discussed based on the results of isothermal anaerobic titrations and 18O-isotopic tests, which confirmed that soot was more likely to react with lattice oxygen species rather than O2, especially at low temperatures. The high mobility of lattice oxygen species was attributed to a combination of the O2− conductivity of Bi2O3 and the accelerative formation of oxygen vacancies at Bi-Co interface. A feasible reaction mechanism over the binary catalysts for soot oxidation was proposed. The stability tests were also studied and the results indicated that Bi-modified Co3O4 showed prominent tolerance against thermal shock, H2O and SO2, thus being a promising active component for practical application.Download high-res image (119KB)Download full-size image

•Pd/γ-Fe2O3 activity for CO oxidation was 2.6 times higher than that of Pd/α-Fe2O3 at 0 °C.•The close contact between Pd and γ-Fe2O3 enhanced the redox recycle between Fe3 + and Fe2 +.•Carbonate absorbed on α-Fe2O3 significantly blocked O2 activation and then inhibited CO oxidation.Pd/Fe2O3 catalysts were prepared by deposition-precipitation method and investigated for CO oxidation. Compared with Pd/α-Fe2O3, Pd/γ-Fe2O3 exhibited the higher CO oxidation activity, and CO completely oxidation temperature was obtained at 0 °C. CO oxidation occurred through the dual sites mechanism, namely CO adsorbed on Pd species and O activation on the support. The close contact between Pd and γ-Fe2O3 enhanced the redox recycle between Fe3 + and Fe2 + species, which played a decisive role in oxygen activation. The excellent performance in oxygen activation efficiently accelerated the rate-determining step in CO oxidation. The accumulated carbonate and hydrocarbonate species on α-Fe2O3 blocked the oxygen activation which resulted in the low activity of Pd/α-Fe2O3 in CO oxidation.Download high-res image (119KB)Download full-size image

A series of perovskite-type LaBO3 (B = Fe, Co, Mn, and Ni) materials have been studied as catalysts for coal bed methane (CBM) deoxygenation. Among them, LaCoO3 shows the best catalytic performance and stability, O2 could be completely eliminated by CH4 to produce CO2 and H2O in the range of 400–720 °C, and the complete deoxidization could be maintained at temperatures of 400, 500, 600, and 660 °C for 100 h. Furthermore, the structure of LaCoO3 could transform from perovskite to Co/La2O3 through La2CoO4/LaCoO3 and La2CoO4/Co3O4 during the process of CBM deoxygenation. The results of H2-TPR and O2-TPO showed the perovskite LaCoO3 is like a smart catalyst, whereby the Co species could reversibly move into and out of the perovskite structure depending on the temperature and reaction atmosphere. When Co species exist in an oxidised state (Co3O4, La2CoO4 and/or LaCoO3), the CH4 in CBM is completely oxidized by O2 to produce CO2 and H2O, the results of isotopic tracer experiments and pulse reaction demonstrate that the reaction follows the Mars–van Krevelen mechanism. However, the preferred products of the CBM deoxygenation reaction are CO and H2 on Co/La2O3 through partial oxidation of CH4. With the structure transforming from Co/La2O3 to LaCoO3 after reoxidation by O2, the activity of CBM deoxygenation could be recovered.

Ceria nanocrystallites with different morphologies and crystal planes were hydrothermally prepared, and the effects of ceria supports on the physicochemical and catalytic properties of Pd/CeO2 for the CO and propane oxidation were examined. The results showed that the structure and chemical state of Pd on ceria were affected by ceria crystal planes. The Pd species on CeO2-R (rods) and CeO2-C (cubes) mainly formed PdxCe1–xO2−σ solid solution with −Pd2+–O2––Ce4+– linkage. In addition, the PdOx nanoparticles were dominated on the surface of Pd/CeO2-O (octahedrons). For the CO oxidation, the Pd/CeO2-R catalyst showed the highest catalytic activity among three catalysts, its reaction rate reached 2.07 × 10–4 mol gPd–1 s–1 at 50 °C, in which CeO2-R mainly exposed the (110) and (100) facets with low oxygen vacancy formation energy, strong reducibility, and high surface oxygen mobility. TOF of Pd/CeO2-R (3.78 × 10–2 s–1) was much higher than that of Pd/CeO2-C (6.40 × 10–3 s–1) and Pd/CeO2-O (1.24 × 10–3 s–1) at 50 °C, and its activation energy (Ea) was 40.4 kJ/mol. For propane oxidation, the highest reaction rate (8.08 × 10–5 mol gPd–1 s–1 at 300 °C) was obtained over the Pd/CeO2-O catalyst, in which CeO2-O mainly exposed the (111) facet. There are strong surface Ce–O bonds on the ceria (111) facet, which favors the existence of PdO particles and propane activation. The turnover frequency (TOF) of the Pd/CeO2-O catalyst was highest (3.52 × 10–2 s–1) at 300 °C and its Ea value was 49.1 kJ/mol. These results demonstrate the inverse facet sensitivity of ceria for the CO and propane oxidation over Pd/ceria.Keywords: ceria crystal plane; CO oxidation; effect of ceria support; propane oxidation; supported Pd catalyst

The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxidation. The activities of In2O3–Co3O4 increased with an increase in In2O3 content, in the form of a volcano curve. Twenty-five wt % In2O3–Co3O4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co3O4. The doping of In2O3 induced the expansion of the unit cell and structural distortion of Co3O4, which was confirmed by the slight elongation of the Co–O bond obtained from EXAFS data. The red shift of the UV–vis absorption illustrated that the electron transfer from O2– to Co3+/Co2+ became easier and implied that the bond strength of Co–O was weakened, which promoted the activation of oxygen. Low-temperature H2-TPR and O2-TPD results also revealed that In2O3–Co3O4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In2O3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co3O4, which tuned the adsorption strength of CO and oxygen activation simultaneously.Keywords: CO adsorption strength; CO oxidation; Co3O4; In2O3; redox ability; surface carbonate species

Highly efficient In2O3–Co3O4 catalysts were prepared for ultralow-temperature CO oxidation by simultaneously tuning the CO adsorption strength and oxygen activation over a Co3O4 surface, which could completely convert CO to CO2 at temperatures as low as −105 °C compared to −40 °C over pure Co3O4, with enhanced stability.

CO adsorption and O2 activation played important roles in CO oxidation on a supported Pd catalyst, which were dependent on the chemical state of Pd. A series of Pd catalysts supported on Al2O3 with different Pd states were prepared: metal Pd (NCR), PdO (NC), Pd2+ coordinated with Cl− (Pd2+–Cl−, CF), and a mixture of PdO and Pd2+–Cl− (CC) and the activity of CO oxidation was in the order NCR ~ CF > CC ≫ NC. The catalysts were characterized by Brunauer, Emmett and Teller (BET) surface area analysis, X-ray diffraction (XRD), temperature programmed reduction by hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results showed that metal Pd (Pd0) could be partially oxidized to Pd+ in the presence of O2, which produced new CO adsorption sites and decreased the CO adsorption strength simultaneously. The cooperation between the enhanced CO adsorption and the decrease in the CO adsorption strength led to high activity for CO oxidation on NCR. For high chemical valence Pd in the species (Pd2+), the chemical environment or coordinated ligand of the Pd species showed large effects on the CO oxidation. The lowest CO oxidation activity on NC occurred when PdO hardly adsorbed CO, meanwhile, PdO was not easily reduced by CO. However, the presence of Cl− significantly promoted the reduction of Pd2+ to Pd+, which increased the amount of CO adsorption and resulted in the higher activity for CO oxidation on CF and CC than PdO. Tuning the CO adsorption by adjusting the chemical state of Pd may be a useful approach to prepare a highly efficient supported Pd catalyst.

Cinchona functionalized mesoporous silica is synthesized by one pot synthesis method. The main silica precursor (TEOS) is co-condensed with a cinchonidine molecule linked organosilane which is renovated by triethoxy silane moiety at its C11 position to yield cinchona functionalized silica. The subsequent deposition of Pt nanoparticles over functionalized silica provides a catalytic system for the enantioselective hydrogenation of α-activated ketone (Orito’s reaction). Thus-developed catalyst system is found to be enantioselective with an enantiomeric excess (e.e) of 35.6%.

Hydrogen can be produced over Er2O3 in methane oxidation (oxygen/methane = 26). The reactivity of lattice oxygen in the catalyst plays a main role in the conversion of surface hydroxyl species to hydrogen or water. Adding a rare earth element into a catalyst can reduce the reactivity of lattice oxygen, resulting in increased hydrogen production, to eliminate catalyst hot-spots.

Pd–Cu–Clx/Al2O3 catalysts were prepared by a NH3 coordination-impregnation method and exhibited an excellent activity for low-temperature CO oxidation and 100% CO conversion was obtained at −30 °C for 400 ppm CO and 1000 ppm H2O/air.

Many properties of dopants have been investigated to explore the key factor that influenced the CO oxidation activity of M-doped ceria (CeM). Nevertheless, these reports were controversial. Herein, the Pauling electronegativity (χP) of the M was presented as a convenient guide to screen a proper dopant for ceria. Kinetics results indicated that the T10 (the temperature when CO conversion reached 10%) of CeM73 catalysts (Ce/M molar ratio was 7/3; M = Cu, Ti, Zr, and Tb) was linearly dependent on the χP of the M, which could adjust the amount of active lattice oxygen (AOL). The AOL was important to catalyst activity because lattice oxygen extraction was the rate-determining step in the overall reaction.

Synthesis of rare earth compound nanosheets with uniform thickness is of potential interest to the luminescent materials. Herein, whole series of rare earth hydrates and oxides nanosheets have been synthesized by using lamellar liquid crystal as a template, except Ce and Pm. Polarizing microscope images and transmission electron microscopy images show that the lamellar liquid crystal can prevent the rare earth hydrate nanosheets from curving to nanotubes in the processes of synthesis. The synthesized nanosheets have a uniform thickness of 10–15 nm and can retain morphology after being calcined at 650 °C. After facile chemical treatment, the functionalized rare earth compounds were obtained, which have unique luminescent property.

Supported coupling catalysts for CS2 removal were prepared with different activated carbons originated from wood, coconut shell and coal as supports, and their catalytic activities for CS2 removal were tested at ambient temperature. The textural and surface properties of the activated carbons were characterized by nitrogen adsorption, temperature-programmed desorption (TPD) and Boehm titration. The activated carbon support with meso- and macropores, and oxygen-functional groups performs higher CS2 removal ability at ambient temperature. The effects of flow rate, CS2 inlet concentration, temperature and relative humidity on CS2 removal were also investigated. High efficient removal is obtained at temperature of 50 °C, space velocity of 2000 h−1, inlet CS2 concentration of 500 mgS/m3 and relative humidity of 20% with the breakthrough sulfur capacity up to 4.3 gS/gCat and working sulfur capacity up to 7 gS/gCat.

Nanoparticles of CexZr1−xO2 (x = 0.75, 0.62) were prepared by the oxidation-coprecipitation method using H2O2 as an oxidant, and characterized by N2 adsorption, XRD and H2-TPR. CexZr1−xO2 prepared had single fluorite cubic structure, good thermal stability and reduction property. With the increasing of Ce/Zr ratio, the surface area of CexZr1−xO2 increased, but thermal stability of CexZr1−xO2 decreased. The surface area of Ce0.62Zr0.38O2 was 41.2 m2/g after calcination in air at 900 °C for 6 h. TPR results showed the formation of solid solution promoted the reduction of CeO2, and the reduction properties of CexZr1−xO2 were enhanced by the cycle of TPR-reoxidation. The Pd-only three-way catalysts (TWC) were prepared by the impregnation method, in which Ce0.75Zr0.25O2 was used as the active washcoat and Pd loading was 0.7 g/L. In the test of Air/Fuel, the conversion of C3H8 was close to 100% and NO was completely converted at λ < 1.025. The high conversion of C3H8 was induced by the steam reform and dissociation adsorption reaction of C3H8. Pd-only catalyst using Ce0.75Zr0.25O2 as active washcoat showed high light off activity, the reaction temperatures (T50) of 50% conversion of CO, C3H8 and NO were 180, 200 and 205 °C, respectively. However, the conversions of C3H8 and NO showed oscillation with continuously increasing the reaction temperature. The presence of La2O3 in washcoat decreased the light off activity and suppressed the oscillation of C3H8 and NO conversion. After being aged at 900 °C for 4 h, the operation windows of catalysts shifted slightly to rich burn. The presence of La2O3 in active washcoat can enhance the thermal stability of catalyst significantly.

Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO2/Al2O3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO3)2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO2 is highly dispersed on the surface of Al2O3 up to 10 wt.% ZrO2, beyond this value tetragonal ZrO2 is formed. The presence of a small amount of ZrO2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO2, but it does not accelerate the activity of 0.2% Pd/ZrO2/Al2O3 for methane combustion. 0.2% Pd/ZrO2/Al2O3 dried at 120 °C shows highest activity for CH4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH4 combustion.

This work investigated the effect of potassium (K) on the catalytic activity of Co3O4 prepared by sol–gel method for soot combustion under loose contact. The catalysts were characterized by XRD, TPR, Raman, FT-IR, and XPS. The results showed the deposition of 4.4 wt.% K accelerated the activity of Co3O4 for soot combustion under loose contact, the temperature of maximum soot oxidation rate (Tm) decreased from 490 °C over Co3O4 to 417 °C over K(0.1)/Co3O4(600). It was discovered that there is an exact linear relationship between Tm and the value of active Co3+/Co for the first time, where Co represented the total amount Co3+ and Co2+. Our findings strongly suggested that potassium, as a promoter, not only favors CB–catalyst contact, but also produces more active Co3+ with the increase of K content. Doped K entered the crystal lattice and aroused the lattice distortion. The Tm in TPO decreased linearly with the increase of microstrain. The lattice distortion and the interaction of K and Co3O4 promoted the formation of the surface active Co3+ and active O−, and improved the activity of lattice oxygen.Graphical abstractDownload high-res image (140KB)Download full-size imageHighlights► The deposition of K accelerated the activity of Co3O4 for soot combustion under loose contact. ► An exact linear relationship between Tm and the value of active Co3+/Co. ► An exact linear relationship between Tm and crystal microstrain of Co3O4 ► K aroused lattice expansion and weakened the Co–O bonds. ► K promoted the formation of the surface active Co3+ sites.

The Co3O4 and Bi2O3–Co3O4 were prepared by precipitation and co-precipitation method. The samples were characterized by XRD, BET, H2-TPR, Raman, XPS and EPR. The low-temperature CO oxidation on the catalysts was also investigated. The results showed the deposition of Bi2O3 enhanced the activity and stability of Co3O4 for CO oxidation. 20 wt.% Bi2O3–Co3O4 could completely convert CO as low as −89 °C, and maintain the complete oxidation of CO at −75 °C for 10 h. XRD and Raman results showed Bi2O3 could enter the lattice of Co3O4, and promote the formation of the lattice distortion and structural defect. H2-TPR results showed that reduction of Co3O4 was promoted and the diffusion of oxygen was accelerated. XPS and EPR results showed the surface richness of Co3+ and the increase of Co2+ in 20 wt.% Bi2O3–Co3O4. The formation of more Co2+ in 20 wt.% Bi2O3–Co3O4 could produce structure defects and lead to the formation of more oxygen vacancy, which was suggested to play the critical role in promoting the catalytic activity and stability of 20 wt.% Bi2O3–Co3O4.Graphical abstractDownload high-res image (152KB)Download full-size imageHighlights► The deposition of Bi2O3 enhances the activity and stability of Co3O4 for CO oxidation. ► 20 wt.% Bi2O3–Co3O4 can completely convert CO as low as −89 °C. ► Bi2O3 promotes the formation of the lattice distortion and structural defect. ► Oxygen vacancy plays the critical role in CO oxidation on 20 wt.% Bi2O3–Co3O4.

CO adsorption and O2 activation played important roles in CO oxidation on a supported Pd catalyst, which were dependent on the chemical state of Pd. A series of Pd catalysts supported on Al2O3 with different Pd states were prepared: metal Pd (NCR), PdO (NC), Pd2+ coordinated with Cl− (Pd2+–Cl−, CF), and a mixture of PdO and Pd2+–Cl− (CC) and the activity of CO oxidation was in the order NCR ~ CF > CC ≫ NC. The catalysts were characterized by Brunauer, Emmett and Teller (BET) surface area analysis, X-ray diffraction (XRD), temperature programmed reduction by hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results showed that metal Pd (Pd0) could be partially oxidized to Pd+ in the presence of O2, which produced new CO adsorption sites and decreased the CO adsorption strength simultaneously. The cooperation between the enhanced CO adsorption and the decrease in the CO adsorption strength led to high activity for CO oxidation on NCR. For high chemical valence Pd in the species (Pd2+), the chemical environment or coordinated ligand of the Pd species showed large effects on the CO oxidation. The lowest CO oxidation activity on NC occurred when PdO hardly adsorbed CO, meanwhile, PdO was not easily reduced by CO. However, the presence of Cl− significantly promoted the reduction of Pd2+ to Pd+, which increased the amount of CO adsorption and resulted in the higher activity for CO oxidation on CF and CC than PdO. Tuning the CO adsorption by adjusting the chemical state of Pd may be a useful approach to prepare a highly efficient supported Pd catalyst.

Highly efficient In2O3–Co3O4 catalysts were prepared for ultralow-temperature CO oxidation by simultaneously tuning the CO adsorption strength and oxygen activation over a Co3O4 surface, which could completely convert CO to CO2 at temperatures as low as −105 °C compared to −40 °C over pure Co3O4, with enhanced stability.

Hydrogen can be produced over Er2O3 in methane oxidation (oxygen/methane = 26). The reactivity of lattice oxygen in the catalyst plays a main role in the conversion of surface hydroxyl species to hydrogen or water. Adding a rare earth element into a catalyst can reduce the reactivity of lattice oxygen, resulting in increased hydrogen production, to eliminate catalyst hot-spots.

Pd–Cu–Clx/Al2O3 catalysts were prepared by a NH3 coordination-impregnation method and exhibited an excellent activity for low-temperature CO oxidation and 100% CO conversion was obtained at −30 °C for 400 ppm CO and 1000 ppm H2O/air.