Catalysts For Total Oxidation Research Articles

Mn and Co decorated biomorphic ceria fiber catalysts for soot and benzene total oxidation.

Mn or Co supported CeO2 fiber catalysts were synthesized following a biotemplating route and evaluated in soot combustion and benzene total oxidation. The catalysts were characterized by SEM, EDX, N2 physisorption, FTIR-ATR, XRD, RAMAN and XPS. SEM results confirmed that the “twisted ribbon” morphology of the biotemplate was mostly maintained. XRD and Raman showed that Mn and Co cations partially insert into ceria lattice and also segregate at the surface of the fibers. XPS allowed to determine that both set of catalysts exhibit Ce3+ and Ce4+ species, in addition to adsorbed and lattice oxygen. Also, the average oxidation state (AOS) of surface Mn could be calculated. Compared to bare Fib Ce, the performances for both reactions were improved for the supported catalysts, except from the catalyst with lowest Mn content for soot combustion. The catalytic activity was discussed in terms of the physicochemical features of the supported catalysts.

Insights into the synergistic effect and catalytic mechanism in MnCeOx solid solution catalysts for low-temperature propane total oxidation

A series of micro-mesoporous MnCeOx solid solution catalysts with various Mn/Ce molar ratios were successfully prepared using a facile chelating sol-gel method, and were studied for the total oxidation of propane. Mn1Ce1Ox exhibited the highest catalytic activity with a T90 = 255.5 ℃, which was 40 ℃ lower than that of pure Mn2O3. The superior performance was owing to the synergistic effect between Mn and Ce in Mn-Ce solid solution structure, which possesses a higher Mn4+/Mn ion ratio, stronger reducibility, and more active oxygen species. Meanwhile, the mechanism on total oxidation of propane over MnOx and MnCeOx was investigated by in-situ DRIFTs and density functional theory calculations. It revealed that Ce did not alter the reaction mechanism, but promoted the adsorption and activation of gaseous O2 on the catalyst surface. Overall, this study will provide more new insights into the catalytic mechanism of volatile organic compounds catalytic oxidation.

Construction of Pd/Mn3O4 heterojunction catalyst for efficient photothermal synergetic catalytic propane total oxidation

Photothermal synergistic low-temperature catalytic volatile organic compounds (VOCs) degradation has an advantage on energy efficiency and reduction of carbon emissions. Herein, an impregnation-pyrolysis-oxidation strategy was adopted to synthesize Pd/Mn3O4 heterojunction catalyst. Under photothermal synergistic conditions, 0.60Pd/Mn3O4 catalyst exhibited an excellent activity for propane total oxidation, with a T90 value of 219.1 ℃, which was 115.3 ℃ lower than that of Mn3O4. Enhancement effect of the heterojunction structure on photothermal synergy was detected by various characterization techniques and density functional theory calculation. The presence of Pd species enhanced the low-temperature reducibility of Mn3O4. Meanwhile, O2 molecules were more easily activated at the Pd sites and overflow to the surface of Mn3O4 for reaction. Besides, the formation of p-n junction between Pd species and Mn3O4 in heterojunction structure promoted the charge separation and the migration of carriers, and boosted the generation of oxygen free radical, resulting in a significant improvement in photothermal catalytic activity. Overall, this study provided new strategy and deep insight for constructing heterojunction to enhance photothermal catalytic performance of VOC elimination.

Performance of nickel-manganese and nickel-cobalt-manganese mixed oxide catalysts in ethanol total oxidation

The mixed oxide catalysts containing Ni, Co, and Mn components in various molar ratios were examined in the total oxidation of ethanol and the effect of their composition on physical chemical properties and catalytic performance was studied. The catalysts were obtained by calcination (4 h at 500 °C in air) of the coprecipitated precursors. The chemical analysis (AAS), powder XRD, Raman spectroscopy, TEM, N2 adsorption, H2-TPR, and XPS were used for the catalysts characterization. Formation of mixed oxides was indicated by powder XRD and Raman spectroscopy: NiCo2O4 spinel together with NiO were detected in the Ni-Co catalysts, MnIV-containing mixed oxides Ni6MnO8 (murdochite) and NiMnO3 (ilmenite) were identified in the Ni-Mn samples, and Ni-Co-Mn mixed oxides with spinel structure were found in the Ni-Co-Mn catalysts. Combination of transition metal components in the catalysts resulted in a synergistic effect; easier reduction in H2-TPR measurements and enhanced catalytic performance compared to single-component Ni, Co, and Mn oxides were observed. Addition of Mn to the Ni and Ni-Co oxides increased their catalytic activity in the ethanol oxidation, which was higher than that of the Ni-Co catalysts. The Ni-Mn catalyst with Ni:Mn molar ratio of 1:1 showed the highest activity (50 % conversion of ethanol was achieved at 91 °C) and good selectivity (acetaldehyde and carbon monoxide were detected as main byproducts of the ethanol oxidation). High activity of the Ni-Mn catalysts can be ascribed to the presence of MnIV-containing mixed oxides, namely NiMnO3. Activity of the Ni-Co-Mn catalysts, especially those with high (Co+Mn) contents, was comparable with that of the most active Ni-Mn catalyst with Ni:Mn molar ratio of 1:1. The high activity of Ni-Co-Mn catalysts can be explained by the formation of spinel-type mixed oxides with rather poor structure ordering and large surface area.

Facile synthesis of highly dispersed Ir/LaFeO3 catalysts for propene total oxidation

A series of Ir/LaFeO3 catalysts calcined at 300–600 °C were synthesized by a solvent-free method and tested for propene total oxidation. Various characterizations depicted that iridium was well-dispersed on LaFeO3 with no detectable iridium-related particles or aggregates. The loading of iridium hardly changed the structural and textural properties of LaFeO3, but greatly enhanced the low-temperature reducibility and oxygen mobility, leading to superior propene oxidation activity. For Ir/LaFeO3 series, the catalytic activity decreased as the calcination temperature increased, due to the declined reducibility and active oxygen species content. Ir/LaFeO3-300 was demonstrated to be the optimal catalyst with the best propene oxidation performance (T90 = 246 °C), excellent long-term stability, and decent water-resistance. Treating Ir/LaFeO3-300 in a reducing atmosphere further improved its catalytic performance by enhancing low-temperature reducibility and increasing surface-active oxygen species. Overall, this study provides insights into the synthesis of highly efficient and stable iridium-based catalysts for VOCs oxidation.

Fabrication of highly dispersed Pd-Mn3O4 catalyst for efficient catalytic propane total oxidation

Adjusting the interaction between dual active components for enhancing volatile organic compounds (VOCs) degradation is an effective but still challenging means of air pollution control. Herein, a limited pyrolysis oxidation strategy was adopted to prepare Pd-Mn3O4 spinel catalysts with uniform morphology and active component dispersion. Among these, 1.08Pd-Mn3O4 presented the highest catalytic efficiency with a T90 value of 240 °C, which was 94 °C lower than that of Mn3O4. Characterization and density functional theory (DFT) calculation results revealed that the strong metal-support interaction (SMSI) effect between Pd and Mn3O4 promoted the redistribution of surface charges, thus strengthening the oxidation-reduction ability of the active sites. Moreover, the SMSI effect led to a better migration of surface oxygen species, and boosted the generation of active surface oxygen species. Simultaneously, the Pd catalyst further reduced the energy barrier in the initial stage of the dehydrogenation of propane. Overall, this study provided a novel design strategy for dual active components catalysts with SMSI effect and extended the application of these catalysts in the important field of VOCs elimination.

Direct Valorization of Recycled Palladium as Heterogeneous Catalysts for Total Oxidation of Methane

Electronic waste as an alternative source of palladium is used for the preparation of heterogeneous catalysts for methane oxidation. The strategy developed in this paper involves two steps: optimization of the leaching protocol to recover the Pd from the waste, and development of a suitable impregnation protocol directly from the leachate, which is a strongly acidic solution. The precipitation-deposition technique is particularly suitable for the preparation of catalysts from acidic media. The impact of Ba, Bi, and Ag impurities on the catalytic performance is studied on model catalysts. The presence of these elements and their impact on the catalytic properties are analyzed and discussed using X-ray diffraction, nitrogen physisorption, scanning and transmission electron microscopy. Through variation of the pH, the impurities co-deposited with Pd can be limited and the catalytic performance of catalysts derived from real waste can be greatly enhanced.

Tailoring Oxygen Vacancies and Active Surface Oxygen Species in Copper-Doped MnO2 Catalysts for Total Catalytic Oxidation of VOCs

Catalytic oxidation has been considered an essential route to tackle volatile organic compounds (VOCs)-driven pollution. To this point, surface engineering has emerged as a robust pathway to promote the efficiency of MnO2-based materials toward VOC oxidation. However, regulating such surface properties has been a critical challenge. This investigation attempts to tailor surface oxygen vacancies and active surface oxygen for the total catalytic oxidation of various VOCs (e.g., formaldehyde, isopropanol, and toluene) via doping copper into cryptomelane and birnessite-type MnO2 catalysts. The catalysts are synthesized by a novel facile successive redox precipitation method between KMnO4 and an ethanol solution containing copper nitrate precursors, followed by annealing. It turns out that the low amount of Cu dopants, corresponding to the copper-to-manganese ratio of 0.17 (RCu/Mn = 0.17), generates a tunnel-structured cryptomelane-type MnO2 with strong bulk oxygen mobility. Such a crystalline structure exhibits the best catalytic performance for the total catalytic oxidation of toluene. The higher copper loading (RCu/Mn = 0.27–0.34) drives the formation of Cu-doped layered birnessite-type MnO2 materials containing rich oxygen vacancies and high active surface oxygen species. Those catalysts promote the oxidation of isopropanol and formaldehyde, respectively. To this end, oxygen vacancies and surface oxygen species crucially steer the molecular oxygen activation and interactions toward adsorbed oxygen species, significantly promoting the total oxidation of isopropanol and formaldehyde, respectively. The explored finding could disclose an outstanding platform toward highly selective and efficient oxidation of VOCs.

The Effect of Metal Ratio and Precipitation Agent on Highly Active Iron-Manganese Mixed Metal Oxide Catalysts for Propane Total Oxidation

Iron-manganese mixed metal oxide catalysts with a range of Fe:Mn ratios were synthesised by co-precipitation using sodium carbonate and evaluated for total propane oxidation. The Fe0.50Mn0.50Ox catalyst was the most active, and this was due to increased surface area along with the formation of a Mn2O3 phase that was not present in the other catalysts. The effect of the precipitating agent was evaluated with the Fe0.50Mn0.50Ox catalyst, investigating preparation using (NH4)2CO3, K2CO3, NH4OH, KOH, and NaOH. In almost all cases, the activity of propane oxidation was increased compared to the Na2CO3-prepared catalyst, with the hydroxide-precipitated catalysts generally being more active than the carbonates. The NH4OH catalyst was the best performing and this was thought to be due to the formation of a highly active mixed defect spinel structure. Results demonstrate that highly active mixed metal oxide total oxidation catalysts can be prepared using abundant elements, and the choice of precipitating agent is important to maximise the activity.

The Influence of Cerium to Manganese Ratio and Preparation Method on the Activity of Ceria-Manganese Mixed Metal Oxide Catalysts for VOC Total Oxidation

A set of ceria-manganese mixed metal oxide catalysts with varying Ce:Mn ratios were prepared by coprecipitation using sodium carbonate and were evaluated for the total oxidation of propane and naphthalene. Manganese-rich samples were the most active, with Ce0.25Mn0.75Ox having the highest activity. Catalysts were characterised using X-ray diffraction, Brunauer–Emmett–Teller (BET) surface area, Raman spectroscopy, temperature programmed reduction (TPR), electron microscopy, and X-ray photoelectron spectroscopy (XPS), establishing that the high activity of Ce0.25Mn0.75Ox was due to the formation of phase-separated Mn-substituted ceria and Mn2O3 phases that were not simultaneously present in the other catalysts. The catalyst preparation technique for the most active ratio was investigated using co-precipitation by urea, oxalic acid and citric acid, and mechanochemical grinding. For propane, the mechanochemical and urea catalysts were more active than the carbonate coprecipitated catalyst, due to greater surface area and increased phase separation. This work demonstrates that ceria-manganese mixed metal oxides are more active than the parent oxide, but that preparation technique is also important for controlling activity.

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.

Low-Temperature Toluene Oxidation on Fe-Containing Modified SBA-15 Materials

Transition metals as catalysts for total VOC oxidation at low temperatures (150-280 °C) are a big challenge nowadays. Therefore, iron-modified SBA-15, AlSBA-15, and ZrSBA-15 materials with 0.5 to 5.0 wt.% Fe loading were prepared and tested for toluene oxidation. It was found that increasing Fe loading significantly improved the rate of oxidation and lowered the temperature of achieving 100% removal of toluene from above 500 °C for the supports (AlSBA-15 and ZrSBA-15) to below 400 °C for 5FeZrSBA-15. The formation of finely dispersed iron oxide active sites with a particle size less than 5 nm was observed on all the SBA-15, AlSBA-15, and ZrSBA-15 supports. It was found that the surface properties of the mesoporous support due to the addition of Al or Zr predetermined the type of formed iron oxide species and their localization on the support surface. Fe-containing SBA-15 and AlSBA-15 showed activity in total toluene oxidation at higher temperatures (280-450 °C). However, 5 wt. % Fe-containing ZrSBA-15 showed excellent activity in the total oxidation of toluene as a model VOC at lower temperatures (150-380 °C) due to the synergistic effect of Fe-Zr and the presence of accessible and stable Fe2+/Fe3+ active sites.

Promoting effect of reduction-oxidation strategy on the Co3O4/γ-Al2O3 catalysts for propane total oxidation

Co3O4/γ-Al2O3 is one of the most active and commonly used catalysts for environmental pollution control. However, the strong Co-Al interaction has seriously deteriorated their catalytic performance, and even affected the promotion effect of an effective improvement strategy. In our previous report, by reasonably adjusting the interaction, the reduction-oxidation (RO) strategy greatly improved its performance. Herein, by constructing a series of 10Co3O4/γ-Al2O3 of enhanced interaction, and treating them by RO strategy, we found that RO strategy improved the activity of all 10Co3O4/γ-Al2O3 for model reaction-propane total oxidation to varying degrees, but the improvement degree is closely related with the interaction strength. In 10CoAl-(500–700) with relatively strong interaction, the improvement was more remarkable than that of 10CoAl-(300–400) with weak interaction and 10CoAl-800 with strong interaction. The maximum reduced values of T50 and T90 are 129 °C and 162 °C over 10CoAl-700, 28 °C and 57 °C higher than that in our previous work. The biggest promoting effect of 10CoAl-(500–700) is the formation and redispersion of active cobalt species, where the latter contributed to the significant increase of 10CoAl-700. The more active Co species produced play a major role in increasing the activity of 10CoAl-(300–400), while weakening of Co-Al interaction slightly increases the activity of 10CoAl-800. This work provided deep insight into the performance improvement of catalysts for air pollution control, and will shed light on catalyst regeneration, design and optimization in the environmental field.

Novel Ceria and Ceria-based Nanocomposites as Potential Catalysts for Methanol Decomposition and Total Oxidation of Ethyl Acetate

The focus of our study is the development of novel ceria-based materials that can be successfully used as catalysts in various environmentally friendly processes due to a significant improvement of ceria intrinsic characteristics. In particular, the combination of ceria with low-dimensional carbon materials such as graphene oxide (GO) and nanodiamond (ND) appears as a very promising approach. Actually, the decrease of ceria crystallite sizes deep in the nanoscale have been found to convert them into highly effective destructive adsorbent materials owing to their high surface area, strong adsorbability, and large number of highly reactive sites. Besides, the addition of a nanostructured carbon containing component (nanodiamond or graphene oxide) contributes to both mechanical and catalytic properties of the obtained nanocomposite hybrids. The results show that the novel ceria and ceria-based composite materials significantly outperform the hydrothermally obtained ceria catalyst used for comparison in both activity and selectivity to CO and hydrogen in the methanol decomposition reaction, and in the process of total oxidation of ethyl acetate due to their significantly improved redox behaviour and textural characteristics.

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.

The promoter effect of Nb species on the catalytic performance of Ir-based catalysts for VOCs total oxidation

Ir/TiO2 catalysts promoted by niobium have been synthesized, characterized by different complementary techniques, and tested for the total oxidation of a set of alkanes and their mixtures. The addition of appropriate amounts of niobium to Ir/TiO2 catalysts resulted in a remarkable increase in the catalytic activity compared to the Nb-free Ir/TiO2 catalysts. The promotion caused by the presence of niobium has been related to the massive presence of isolated IrOx surface species which, interestingly, present remarkable reducibility and, consequently, excellent catalytic activity. Conversely, the IrOx species formed in the catalyst in the absence of niobium also include IrO2 clusters with lower intrinsic reactivity. Similarly, Nb-loadings exceeding the theoretical monolayer tends to the formation of bulk Nb2O5 species on the titania surface that provokes the formation of IrO2 nanoclusters. A positive influence on the reactivity of non-stoichiometric surface Ti3+ species that generates oxygen vacancies is also observed.

Design Control of Copper-Doped Titania–Zirconia Catalysts for Methanol Decomposition and Total Oxidation of Ethyl Acetate

This study is focused on the design control of Cu–Zr–Ti oxide composites by the variation of the Zr/Ti ratio and the copper deposition procedure used. For the first time, these ternary composites were obtained by a combination of template-assisted hydrothermal techniques for the preparation of mesoporous ZrO2–TiO2 mixed oxides with diverse compositions, followed by the consecutive chemisorption and hydrolysis of copper ammonia complexes on them. The nitrogen physisorption, XRD, SEM, HRTEM, TPR, XPS, UV-Vis, and Raman spectroscopies were applied for the catalysts’ characterization. Methanol decomposition and the total oxidation of ethyl acetate, both of which with potential for sustainable environmental protection, were used as catalytic tests. The complex relationship between the phase composition, structure, and morphology of titania–zirconia mixed oxides and the state and catalytic behavior of the copper oxide species supported on them was investigated. In comparison with the conventional impregnation technique, the novel preparation procedure revealed the generation of more uniform and homogeneously dispersed needle-like copper oxide crystallites in the mesoporous TiO2–ZrO2 host matrix, which typically ensure improved catalytic performance. The synergistic activity between the loaded copper species and TiO2–ZrO2 support was discussed. All ternary composites exhibited superior catalytic activity in total oxidation of ethyl acetate. The specific behavior of the catalysts in methanol decomposition was related to the irreversible phase transformations by the influence of the reaction medium.

Mixed oxides of cerium and manganese as catalysts for total oxidation of ethyl acetate: effect of preparation procedure

Mixed oxides of cerium and manganese as catalysts for total oxidation of ethyl acetate: effect of preparation procedure

Hydrothermal-treated Pt/Al2O3 as an excellent catalyst for toluene total oxidation

The preparation of highly active supported noble metal catalysts with a low noble metal loading has always been the ultimate goal of researchers working on catalysis. Hydrothermally treated Pt/Al2O3 (Pt/Al2O3-H) exhibits better catalytic activity than that (Pt/Al2O3-C) treated via the conventional calcination approach. At the high space velocity of 100,000 mL/(g∙hr), the temperature that correspond to 50% toluene conversion (T50) of Pt/Al2O3-H is 115°C lower than that of Pt/Al2O3-C, and the turnover frequency (TOF) value can reach 0.0756 sec−1. The mechanism by which the hydrothermal approach enhances Pt/Al2O3 activity has been investigated. The structure associated with the high catalytic activity of Pt nanoparticles (NPs) can be retained via hydrothermal treatment. Furthermore, the support is transformed to AlO(OH) with numerous surface hydroxyl groups, which in turn can facilitate the adsorption of toluene. And the synergistic effects of Pt NPs and AlO(OH) increases the contents of Pt in oxidation state and active oxygen, which are beneficial for toluene oxidation.

Insight into the pH effect on the oxygen species and Mn chemical valence of Co–Mn catalysts for total toluene oxidation

Mn-Based metal oxides have shown promising performance in catalytic oxidation of toluene due to the mixed Mn3+ and Mn4+ valences and in large numbers of oxygen vacancy clusters on the surface.