H2 Temperature-programmed Reduction Results Research Articles

Investigation of Ce/BEA as a passive NOx adsorber: 2. Hydrothermal aging deactivation mechanism

Ce/BEA has the potential to be applied as a novel passive NOx absorber (PNA) in the after-treatment of vehicles due to its considerable NOx storage capacity. However, as a vehicle exhaust after-treatment material, it must withstand the test of long-term hydrothermal aging. This work examined the deactivation mechanism of Ce/BEA during hydrothermal aging. 3.0 wt% Ce/BEA was prepared using the ion-exchange method, and then subjected to hydrothermal treatment at 650 °C with 10% H2O for 1–12 h to obtain samples with different aging extent. For comparison, the H-BEA support was aged under the same conditions. Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD), NH3 temperature programmed reduction (NH3-TPD), 27Al MAS nuclear magnetic resonance (27Al MAS NMR), H2 temperature programmed reduction (H2-TPR), and high resolution-transmission electron microscopy (HR-TEM) were performed to characterize the changes in PNA performance, structure, Ce species, and acidity. The HR-TEM and H2-TPR results show that CeOx particles appear after hydrothermal aging, which results from the detachment and aggregation of active Ce species. Based on the 27Al MAS NMR results, we conclude that BEA zeolite dealumination leads to the loss of acidic sites and the transformation of active Ce species on the acidic sites into the less active CeOx. This is the primary reason for the hydrothermal aging deactivation of Ce/BEA.

Highly active and water tolerant Pt/MFe2O4 (M = Co and Ni) catalysts for low temperature CO oxidation

Pt supported on CoFe2O4 and NiFe2O4 spinel oxides were much more active for low temperature CO oxidation compared to those supported on monometallic oxides (i.e. Co3O4, Fe2O3 and NiO). The Pt/CoFe2O4 catalyst gave the best performance, with a turnover frequency of 0.27 s−1 at 50 ℃, which was three times as high as that on the Pt/Fe2O3. The interaction between Pt and the spinel oxide facilitated the activation of the oxygen species as evidenced by the H2 temperature programmed reduction results, and weakened the adsorption strength of CO on the Pt atoms as revealed by the in situ diffuse reflectance infrared Fourier transform spectroscopy results and kinetic investigation. These facts accounted for the enhanced reactivity. Moreover, the catalysts exhibited excellent water tolerance, which maintained activity even under 10 vol.% water vapor in the feed stock. Therefore, these catalysts are promising for practical applications.

Flame spray pyrolysis synthesized CuO–CeO2 composite for catalytic combustion of C3H6

C3H6 is a typical volatile organic compound (VOC) which is greatly harmful to the environment, however, it is difficult to achieve a complete C3H6 removal at low temperature via the catalytic combustion treatment. In this study, high-performance catalysts of CuOCeO2 composites were synthesized via a modified flame spray pyrolysis (FSP) method for the catalytic combustion of C3H6. The CuOCeO2 composites with different Cu molar ratios of 10, 25, 35, 50, and 75% were characterized by N2 sorption-desorption analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). Results show that the composites preserve a nanometer-sized structure with stable micromorphology, which is hardly affected by the molar ratio of Cu. The FSP method is confirmed to be capable of producing solid solution oxides in the composites, which provide abundant reactive oxygen species and good reducibility. XPS, H2-TPR results indicate that Cu loading content has a significant impact on the catalytic properties of the prepared CuOCeO2 catalysts by influencing the content of the solid solution. Compared with other methods, the optimized FSP method can significantly improve the loading of Cu without producing large crystalline CuO particles on the catalyst surface. C3H6 conversion reached a 90% conversion at 380 °C indicating an outstanding catalytic performance of the FSP-synthesized CuOCeO2 catalysts with 35 mol% Cu loading. Moreover, the ignitability of C3H6 is also affected by the catalyst's physicochemical properties, and different active species play the main role in different temperature intervals.

Highly dispersed Pd/modified-Al2O3 catalyst on complete oxidation of toluene: Role of basic sites and mechanism insight

Noble metal catalysts face high cost and limited resources challenge. Developing a high efficiency catalyst with low noble metal loading is an important way to meet this challenge. In this study, Mg-, Ba- and Zr-doped Pd/Al2O3 catalysts with Pd loading of 0.5 wt% were prepared by stepwise wet impregnation method and used for complete oxidation of toluene. These catalysts were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), CO chemisorption, hydrogen temperature-programmed reduction (H2-TPR), temperature-programmed desorption of CO2 (CO2-TPD) and temperature-programmed desorption of oxygen (O2-TPD). Catalytic reaction of toluene and isopropyl alcohol were carried out in a fixed bed micro-reactor under the condition of GHSV = 24,000 ml h−1gcat−1 with 500 ppm toluene or isopropyl alcohol. The results of XRD, Raman and XPS revealed that PdO is the major species in all of the catalysts. The size of PdO remarkably decreased on MgO-doped Al2O3 surface. The results of H2 temperature-programmed reduction and O2 temperature-programmed desorption indicated that the reducibility of PdO and the active oxygen species were enhanced by doping basic element. In situ diffusion reflectance-infrared Fourier transform spectroscopy proved that benzaldehyde and carboxylates were the intermediate products of toluene oxidation. The results of X-ray photoelectron spectroscopy on used catalysts demonstrated that many more Pd2+ species were detected in Pd/MgO-Al2O3 sample, suggesting that a Pd2+/Pd0 pairs was formed which is favored to the combustion of toluene. The results show that the catalytic performance of Pd/Al2O3 was promoted by modifying basic oxides in the order of Pd/MgO-Al2O3 > Pd/BaO-Al2O3 > Pd/ZrO2-Al2O3 > Pd/Al2O3. The catalytic activity of 0.5 wt% Pd/MgO (2.0 wt%)-Al2O3 was similar with that of 1.0 wt% Pd/Al2O3.

Investigation of an irreversible NOx storage degradation Mode on a Pd/BEA passive NOx adsorber

Passive NOx adsorbers (PNAs) are a proposed solution for cold start NOx emissions, via low temperature NOx trapping and subsequent release at a temperature where downstream NOx reduction catalysts are active. Pd/zeolites have been reported to have significant NOx storage capacities. However, their real exhaust compatibility has not been completely evaluated. In this work, Pd/BEA was used to study the mechanism of an observed PNA degradation. NO adsorption, NO and CO co-adsorption and temperature programmed desorption/oxidation were performed on a series of differently aged Pd/BEA catalysts to evaluate the NOx storage capacity and desorption temperature. An irreversible NOx storage degradation mode caused by low temperature CO exposure was observed. H2 temperature programmed reduction results indicate this irreversible degradation can be attributed to the loss of Pd2+. Additionally, STEM images revealed Pd particle migration/agglomeration after hydrothermal aging and CO/H2 exposure. Larger particles, formed during CO exposure, lead to the irreversible degradation.

Enhanced catalytic activity towards formaldehyde oxidation over Ag catalysts supported on carbon nanotubes

In this paper, highly active Ag catalysts supported on carbon nanotubes (CNTs) were synthesized by impregnation and two kinds of simple one step co-reduction methods with reducing agents of glycerol and dimethyl sulfoxide (denoted as IM, GL and DMSO sample). The catalysts were characterized by N2 adsorption–desorption, X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy, transmission electron microscopy, UV–visible spectrometer, infrared spectrometry, X-ray photoelectron spectroscopy (XPS) and H2 temperature programmed reduction (H2-TPR). DMSO sample showed the high reaction activity, above 90% HCHO conversion at 150 °C, whereas its surface Ag content is only less than ten times of IM sample in DMSO sample. The XRD, SEM, BET analysis, XPS and H2-TPR results revealed that the highly dispersed Ag/CNTs prepared by chemical reduction method in DMSO sample showed a smaller silver particles size, high surface areas and the enriched surface oxygen species. In general, the highest activity of DMSO samples in HCHO oxidation was associated with its higher silver dispersion and the strong interaction between Ag and CNTs, thereby increasing the effectiveness of oxygen mobility.

Spectroscopic study of microstructure-reducibility relation of CexZr1−xO2 solid solutions

We have successfully elucidated the microstructures of CexZr1−xO2 solid solutions prepared by co-precipitation and their relation with the reduction behaviors. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy results demonstrate that Zr(IV) occupies initially substituting site and then interstitial site in cubic CeO2. The accumulation of Zr(IV) in interstitial site induces the gradual phase transition from cubic phase to tetragonal phase. The results of selective chemisorption of methyl orange demonstrate that the substituting-site doping of Zr(IV) preferentially occurs in the bulk and then extends to the outmost surface. H2 temperature-programmed reduction results indicate that the substituting-site doping of Zr(IV) mainly enhances the reducibility of Ce(IV) whereas the interstitial-site doping of Zr(IV) not only enhances the reducibility of Ce(IV) but also lowers the activation energy of reduction reaction. These results provide novel insights into the microstructure-reducibility relation of CexZr1−xO2 solid solutions.

Ni nanoparticles encapsulated in the channel of titanate nanotubes: Efficient noble-metal-free catalysts for selective hydrogen generation from hydrous hydrazine

Ni nanoparticles were encapsulated in the channel of titanate nanotubes (TNTs) by the capillary forces under ultrasonic treatment (Ni@TNTs). The structure and properties of the catalyst were studied by scanning electronic microscopy (SEM), transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), CO chemisorption and N2 adsorption–desorption, respectively. The TEM, EDX and N2 adsorption–desorption results demonstrated that Ni nanoparticles (NPs) were encapsulated in the channel of TNTs successfully. The results of XRD, H2-TPR and XPS indicated a strong metal-support interaction between Ni NPs and TNTs. Ni@TNTs exhibited a good catalytic performance for the decomposition of hydrous hydrazine which was due to the small nanoparticle size and high dispersion of Ni NPs after encapsulation in the channel of TNTs. The catalyst could be recycled six times without significant loss in catalytic activity, which was attributed that the confinement of TNTs prevents Ni NPs from leaching or aggregation. The design strategy for NPs confined in nanotubes may have potential applications in many heterogeneous reactions.

Catalytic Combustion of Vinyl Chloride Emission over a TiO2–MnOx Catalyst

TiO2–MnO x catalyst samples with different Ti/(Ti + Mn) molar ratios (2:3, 3:4, 4:5, 5:6, 6:7 and 1) prepared by the citric acid (CA) sol-gel method were studied in the catalytic combustion of vinyl chloride (VC) emission. The effects of preparation conditions and operation parameters on the catalytic performance of TiO2–MnO x were investigated. The catalyst samples were characterised by N2 adsorption, X-ray diffraction (XRD) and H2-temperature programmed reduction (H2-TPR). In the catalytic combustion of VC over TiO2–MnO x, products containing HCl, CO2, and H2O were obtained and there were no by-products such as chlorohydrocarbons and chlorine. The TiO2–MnO x catalyst with the molar ratio of CA/Mn/Ti = 0.30:0.20:0.80 showed the best catalytic performance and had better operating flexibility over the ranges of gas hourly space velocity (GHSV) of 15000–100000 h−1 and VC concentration of 0.05–2.00%. The temperatures at 50% conversion (140 °C) and at 99% conversion (220 °C) were achieved at a VC concentration of 0.1% and GHSV of 15000 h−1. XRD characterisation indicated that only the characteristic diffraction peaks of TiO2 with the anatase structure appeared and no characteristic diffraction peaks of MnO x species appeared for the TiO2–MnO x catalyst. XRD and H2-TPR results indicated that Mn ions were incorporated into the TiO2 lattice to form a Ti–Mn–O solid solution, which enhanced the reactivity of active oxygen species on the catalyst surface and thereby promoted the catalyst activity.

Preparation and characterization of Ce1−xPrxO2 supports and their catalytic activities

In this work, the addition of praseodymium (Pr) into ceria as a mixed oxide support in a form of Ce1−xPrxO2 (x = 0.01, 0.025, 0.050, 0.075 and 0.10) was prepared using a co-precipitation method. The structural and textural properties of the synthesized supports were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, Raman spectroscopy, H2-temperature programmed reduction (H2-TPR) and H2-chemisorption. Upon addition of Pr, XRD patterns and Raman spectra indicated an enlargement of ceria unit cell and the characteristics Raman broad peak at 570 cm−1 which was attributed to the existence of oxygen vacancies in the ceria lattice. This indicated that some Ce4+ ions in ceria were replaced by larger Pr3+ cations. To evidence the incorporation of Pr3+ cations into ceria lattice, X-ray absorption near edge structure (XANES) was employed. The results showed that the oxidation states of Ce in mixed oxide supports were slightly lower than 4+ while those of Pr were still the same as a precursor salt. Therefore, the incorporation of Pr3+ into ceria lattice would lead to strain and unbalanced charge and result in oxygen vacancies. The reducibility of Ce1−xPrxO2 mixed oxide supports was investigated by H2-TPR and temperature-resolved X-ray absorption spectroscopy experiment under reduction conditions. XANES spectra of Ce L3 edges showed a lower surface reduction temperature (Ce4+ to Ce3+) of Ce0.925Pr0.075O2 than that of CeO2 which agreed with H2-TPR results. H2-chemisorption indicated that Pr promoted the dispersion of the metal catalyst on the mixed oxide support and increased the adsorption site for CO. For WGS reaction, 1% Pd/mixed oxide support had higher WGS activity than 1% Pd/ceria. The increase of WGS activity was due to the increase of Pd dispersion on the support and the existence of oxygen vacancies produced from incorporation of Pr into the ceria lattice.

Influence of the oxide support reducibility on the CO2 methanation over Ru-based catalysts

Catalysts consisting of 5wt.% ruthenium dispersed on four different metal oxide supports were synthesized with single-step flame spray pyrolysis and assessed for the hydrogenation of CO2. The chosen supports covered a variety of characteristics expected to alter the catalytic performance, ranging from amphoteric and irreducible Al2O3, to amphoteric and reducible ZnO and MnOx, to basic and reducible CeO2. For the pristine metal oxide supports, the catalytic activity correlated with the oxide basicity and ZnO showed the highest CO2 conversion. However, CO formation through the reverse water-gas shift reaction dominated over the CO2 methanation due to a lack of H2 dissociation sites. The addition of Ru created such H2 dissociation sites and a significant increase in CO2 conversion and CH4 selectivity was observed. Combining the results of H2 temperature-programmed reduction, quantitative H2 and CO chemisorption, in situ DRIFTS, and the CO2 hydrogenation reaction kinetics revealed that the Ru coverage with CO decreased with the support reducibility. For the irreducible Al2O3 support, the Ru particles were quasi-saturated with CO at low temperatures and the reaction was limited by the competitive Langmuir-type co-adsorption of H2. The ZnO support lead to the lowest Ru-CO coverage associated with a weak CO adsorption and the reaction was dominated by the reverse water-gas shift reaction. CeO2 showed a Ru-CO coverage in between Al2O3 and ZnO, which ensured the presence of H2 dissociation sites while the Ru-CO adsorption strength remained sufficiently high.

Catalytic combustion of volatile aromatic compounds over CuO-CeO2 catalyst

Ce1−x Cu x O2 oxide solid solution catalysts with different Ce/Cu mole ratios were synthesized by the one-pot complex method. The prepared Ce1−x Cu x O2 catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR). Their catalytic properties were also investigated by catalytic combustion of phenyl volatile organic compounds (PVOCs: benzene, toluene, xylene, and ethylbenzene) in air. XRD analysis confirmed that the CuO species can fully dissolve into the CeO2 lattice to form CeCu oxide solid solutions. XPS and H2-TPR results indicated that the prepared Ce1−x Cu x O2 catalysts contain abundant reactive oxygen species and superior reducibility. Furthermore, the physicochemical properties of the prepared Ce1−x Cu x O2 catalysts are affected by the Ce/Cu mole ratio. The CeCu3 catalyst with Ce/Cu mole ratio of 3.0 contains abundant reactive oxygen species and exhibits superior catalytic combustion activity of PVOCs. Moreover, the ignitability of PVOCs is also affected by the respective physicochemical properties. The catalytic combustion conversions of ethylbenzene, xylene, toluene, and benzene are 99%, 98.9%, 94.3%, and 62.8% at 205, 220, 225, and 225 °C, respectively.

Template-Mediated Ni(II) Dispersion in Mesoporous SiO2 for Preparation of Highly Dispersed Ni Catalysts: Influence of Template Type.

Supported Ni catalysts on three mesoporous SiO2 supports (i.e., SBA-15, MCM-41, and HMS) were prepared using a solid-state reaction between Ni(NO3)2 and organic template-occluded mesoporous SiO2. For comparison, supported Ni catalysts on mesoporous SiO2 synthesized by the conventional impregnation method were also included. The catalysts were characterized by scanning electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, N2 adsorption, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, transmission electron microscopy, and transmission electron microscopy-energy-dispersive X-ray. The catalytic properties of the catalysts were evaluated using gas-phase catalytic hydrodechlorination of 1,2-dichloroethane. The results showed that upon grinding Ni(NO3)2 with template-occluded mesoporous SiO2, strong coordination between Ni2+ and dodecylamine was identified in the Ni(NO3)2-HMS system. Additionally, the results of H2 temperature-programmed reduction revealed that NiO in calcined NiO/HMS was reduced at higher temperature than those in calcined NiO/SBA-15 and NiO/MCM-41, reflecting the presence of a strong interaction between NiO and mesoporous SiO2 in NiO/HMS. Consistently, the average particle sizes of metallic Ni were found to be 2.7, 3.4, and 9.6 nm in H2-reduced Ni/HMS, Ni/SBA-15, and Ni/MCM-41, respectively, indicative of a much higher Ni dispersion in Ni/HMS. For the catalytic hydrodechlorination of 1,2-dichloroethane, Ni/MCM-41 synthesized by the solid-state reaction method exhibited a catalytic activity similar to that prepared by the impregnation method, while higher catalytic activities were observed on Ni/HMS and Ni/SBA-15 than on their counterparts prepared by the impregnation method. Furthermore, a higher conversion was identified on Ni/HMS than on Ni/SBA-15 and Ni/MCM-41, highlighting the importance of template type for the preparation of highly dispersed metal catalysts on mesoporous SiO2.

Hydrogen Production from Steam Reforming of Acetic Acid over Ni-Fe/Palygorskite Modified with Cerium

The steam reforming of acetic acid (SRA) was carried out in a fixed-bed tubular reactor with Ni-Fe/ceria-palygorskite (CPG) catalysts. The as-prepared catalysts were analyzed by N2 adsorption-desorption, scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), H2 temperature programmed reduction (H2-TPR), and X-ray diffraction (XRD). The results of H2-TPR and XRD showed that the addition of CeO2 increased the hydrogen consumption of catalysts and the interaction force between active component (Ni-Fe alloy) and carrier. Moreover, the Ni-Fe alloys were successfully synthesized in the Ni-Fe/CPG catalysts and their crystallite sizes were decreased by adding CeO2. In addition, these catalysts were employed to SRA at 600 °C, GHSV = 14427 h-1 and different molar ratio of S/C. The experimental results revealed that the Ni-Fe/C0.4PG0.6 catalyst can achieve the highest yield of H2 (87%) and HOAc conversion (95%), as well as the highest stability during the process of steam SRA. Additionally, the spent catalysts were characterized by XRD, SEM, and thermogravimetric analysis (TGA). The results showed that the addition of CeO2 enhanced the stability and activity of Ni-Fe/palygorskite catalyst and reduced the coke deposition rate on the catalyst surface.

Effects of potassium promoter on the performance of PdCl 2 –CuCl 2 /AC catalysts for the synthesis of dimethyl carbonate from CO and methyl nitrite

The effect of potassium (K) promoter on the catalytic performance of activated carbon (AC) supported Wacker-type catalysts (PdCl2–CuCl2/AC) for the synthesis of dimethyl carbonate (DMC) from CO and methyl nitrite (MN) was investigated by means of N2 adsorption, H2-temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the space time yield of DMC on Wacker-type catalysts with different K promoters ranked in the following order: KCl > KOH > CH3COOK > K2CO3. Especially, the addition of KCl significantly improved the catalytic activities of PdCl2–CuCl2/AC catalyst for DMC synthesis from CO and MN. N2 adsorption data indicated that the addition of K promoters did not change the textural properties of Wacker-type catalysts greatly. H2-TPR and XPS results demonstrated that the existence of KCl promoted the reducibility of Cu2+ species and increased the proportion of Cu2+ species on catalyst surface, which is favorable for oxidizing Pd0 to active Pd2+. Further, the addition of KCl benefited the reactivity of PdCl2–CuCl2/AC catalyst for DMC synthesis from CO and MN.

Higher Oxidation State Responsible for Ozone Decomposition at Room Temperature over Manganese and Cobalt Oxides: Effect of Calcination Temperature

The heterogeneous catalytic decomposition of ozone was investigated over unsupported manganese and cobalt oxide at room temperature. All catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption (Brunauer–Emmet–Teller method), H2-temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity test indicated that these oxides had a good activity on ozone conversion meanwhile the catalysts remained highly active over time under reaction conditions. The treated temperature of the catalyst had a significant impact on the performance of ozone abatement and the samples treated at lower temperature showed higher activity. The surface area decreased obviously when developing the calcination temperature and H2-TPR results demonstrated that much higher oxidation state of metal ions and active oxygen species were maintained on the surface under low treated temperature. XPS analysis showed that there were higher oxidation states of metal ions (Mn4+ and Co3+) and adsorbed oxygen species on the surface of catalysts treated at lower temperature, both of which play a significant role in ozone decomposition. However, the activity of manganese oxide was higher than that of cobalt oxide and the possible reason for this phenomenon was discussed.

Comparative study on the catalytic CO oxidation properties of CuO/CeO2 catalysts prepared by solid state and wet impregnation

A series of CuO/CeO2 catalysts were prepared by solid state impregnation (SSI) and wet impregnation (WI) methods and characterized by X-ray diffraction, H2 temperature-programmed reduction (H2-TPR), laser Raman spectroscopy (LRS), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and X-ray photoelectron spectroscopy (XPS). XPS and H2-TPR results showed that SSI increased the dispersion of the copper species on the catalyst surface, which benefited the reduction of CuO species. LRS results indicated that a higher concentration of oxygen vacancies was obtained by the SSI method unlike the WI method. CO oxidation results showed that at a given CuO loading, the activity of the catalysts prepared by SSI was higher than that of their counterparts prepared by WI. Based on the combined characterization results, it was suggested that the enhanced activity was closely related to the higher concentrations of oxygen vacancies and Cu+-CO species on the catalysts. Last, a possible synergetic mechanism was proposed for CO oxidation over the CuO/CeO2 catalysts.

Catalytic oxidation of benzene over Ce–Mn oxides synthesized by flame spray pyrolysis

Flame spray pyrolysis (FSP) was utilized to synthesize Ce–Mn oxides in one step for catalytic oxidation of benzene. Cerium acetate and manganese acetate were used as precursors. The materials synthesized were characterized using X-ray diffraction (XRD), N2 adsorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and H2-temperature programmed reduction (H2-TPR) and their benzene catalytic oxidation behavior was evaluated. Mn ions were evidenced in multiple chemical states. Crystalline Ce–Mn oxides consist of particles with size <40nm and specific surface areas (SSA) of 20–50m2/g. Raman spectrums and H2-TPR results indicated the interaction between cerium and manganese oxides. Flame-made 12.5%-Ce–Mn oxide exhibited excellent catalytic activity at relatively low temperatures (T95 about 260°C) compared to other Ce–Mn oxides with different cerium-to-manganese ratios. Redox mechanism and strong interaction conform to structure analysis that Ce–Mn strong interaction formed during the high temperature flame process and the results were used to explain catalytic oxidation of benzene.

Low-temperature selective catalytic reduction of NO with NH3 over nanoflaky MnOx on carbon nanotubes in situ prepared via a chemical bath deposition route

Nanoflaky MnO(x) on carbon nanotubes (nf-MnO(x)@CNTs) was in situ synthesized by a facile chemical bath deposition route for low-temperature selective catalytic reduction (SCR) of NO with NH₃. This catalyst was mainly characterized by the techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N₂ adsorption-desorption analysis, X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR) and NH₃ temperature-programmed desorption (NH₃-TPD). The SEM, TEM, XRD results and N₂ adsorption-desorption analysis indicated that the CNTs were surrounded by nanoflaky MnO(x) and the obtained catalyst exhibited a large surface area as well. Compared with the MnO(x)/CNT and MnO(x)/TiO₂ catalysts prepared by an impregnation method, the nf-MnO(x)@CNTs presented better NH₃-SCR activity at low temperature and a more extensive operating temperature window. The XPS results showed that a higher atomic concentration of Mn(4+) and more chemisorbed oxygen species existed on the surface of CNTs for nf-MnO(x)@CNTs. The H₂-TPR and NH₃-TPD results demonstrated that the nf-MnO(x)@CNTs possessed stronger reducing ability, more acid sites and stronger acid strength than the other two catalysts. Based on the above mentioned favourable properties, the nf-MnO(x)@CNT catalyst has an excellent performance in the low-temperature SCR of NO to N₂ with NH₃. In addition, the nf-MnO(x)@CNT catalyst also presented favourable stability and H₂O resistance.

Controlled preparation and characterization of supported CuCr2O4 catalysts for hydrogenolysis of highly concentrated glycerol

Supported Cu–Cr catalysts were prepared by a non-alkoxide sol–gel route, and characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), H2-temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) measurement. Their structures were significantly tuned by the Cu–Cr molar ratio. CuCr2O4, CuCr2O4–CuO and CuCr2O4–Cr2O3 structures were confirmed in CuCr(0.5), CuCr(4) and CuCr(0.25) catalysts, respectively. A direct interaction between CuCr2O4 and CuO or Cr2O3 in CuCr(4) and CuCr(0.25) catalyst was observed by the H2-TPR and XPS results. The catalytic performance of Cu–Cr catalysts with various structures was examined by hydrogenolysis reaction of high concentrated glycerol. Under mild conditions (2.0 MPa and 130 °C) and high concentration (100 wt%), the maximum conversion (52%) was obtained over the CuCr(0.5) catalyst, while the CuCr(4) catalyst gave the highest selectivity of 1,2-PD (up to 100%). This finding will result in the production of less waste water and lower energy consumption in the following separation steps during glycerol hydrogenolysis.