Abundant Acid Sites Research Articles

Synergistic effect of Pt/Ce and USY zeolite in Pt-based catalysts with high activity for VOCs degradation

Pt/Ce-USY catalysts were synthesized by ethylene glycol reduction (r) and ion exchange (ex) methods, respectively, and the synergistic effect of Pt/Ce and USY zeolite was investigated for VOCs removal at low-temperature. For 1,2-dichloroethane (DCE) degradation, Pt/Ce-USY catalysts doped with CeO2 exhibit more superior activity than Pt/USY catalysts, which owes to the synergistic effect between the abundant acid sites (especially strong acidity) and strong oxidizing sites. While for non-chlorinated VOCs degradation, Pt/USY-r and Pt/Ce-USY-r catalysts both exhibit pretty good low-temperature activity and give the very low T90 values for benzene, ethyl acetate and n-hexane degradation, resulting from the active Pt species dispersed on the surface of USY zeolite. Moreover, loading Pt significantly promotes the deep oxidation of CH3Cl and C2H3Cl intermediates to CO2 and inhibits the deposition of carbon species, thus increases the durability of the catalyst for VOCs degradation, principally, benefiting from the strong Pt-CeO2 interaction.

New insights into the relationships between performance and physicochemical properties of FeOx–NbOx mixed oxide catalysts for the NH3-SCR reactions

In this study, we prepared Fe2O3–Nb2O5 binary mixed oxide catalysts using co-precipitation (CP), sol-gel (SG), and solid process (SR) methods and tested their performance. All the catalysts exhibited over 75% NOx removal efficiency between 250 °C and 400 °C. Compared with the samples prepared by the SR method, catalyst synthesized using CP and SG methods possessed a larger specific surface area, which could compensate for the lower surface area-normalized reaction rate originating from the insufficient reactive surface oxygen species, hence exhibiting a relatively high low-temperature apparent deNOx activity. However, at a high-temperature region, limited amount of reactive surface oxygen species, together with abundant strong acid sites, facilitated the proceeding of NH3 reduction of NOx, which well explained the higher apparent activity of the catalyst prepared by SG method than the other two samples. It seemed that specific surface area had an important role to play in the low-temperature apparent performance of the catalysts, while chemical properties mainly decided the activity at an elevated temperature.

Chlorine-Resistant Hollow Nanosphere-Like VOx/CeO2 Catalysts for Highly Selective and Stable Destruction of 1,2-Dichloroethane: Byproduct Inhibition and Reaction Mechanism

Developing economical and robust catalysts for the highly selective and stable destruction of chlorinated volatile organic compounds (CVOCs) is a great challenge. Here, hollow nanosphere-like VOx/CeO2 catalysts with different V/Ce molar ratios were fabricated and adopted for the destruction of1,2–dichloroethane (1,2–DCE). The V0.05Ce catalyst possessed superior catalytic activity, reaction selectivity, and chlorine resistance owing to a large number of oxygen vacancies, excellent low-temperature redox ability, and chemically adsorbed oxygen (O− and O2−) species mobility. Typical chlorinated byproducts (CHCl3, CCl4, C2HCl3, and C2H3Cl3) derived from the cleavage of C–Cl and C–C bonds of 1,2–DCE were detected, which could be effectively inhibited by the abundant acid sites and the strong interactions of VOx species with CeO2. The presence of water vapor benefited the activation and deep destruction of 1,2–DCE over V0.05Ce owing to the efficient removal of Cl species from the catalyst surface.

One-pot Synthesis of Acetals by Tandem Hydroformylation-acetalization of Olefins Using Heterogeneous Supported Catalysts

A green route for one−pot synthesis of acetals by tandem hydroformylation−acetalization of olefins using supported Rh−based catalysts was developed. Experimental results demonstrated that suitable Rh loading (1 wt%) with appropriate reaction temperature (120 °C) and reaction time (8 h) were favorable for the formation of acetals, and a high acetals selectivity of 94.6% was achieved. More importantly, the selectivity to valuable linear products was enhanced in this tandem catalysis. Based on the catalytic mechanism study, highly dispersed RhOx nanoparticles and abundant acid sites on the supports were responsible for the hydroformylation and acetalization, respectively. One-pot synthesis of acetals directly from olefins with high selectivity was achieved over heterogeneous bifunctional catalysts via tandem hydroformylation-acetalization.

Synthesis of cyclohexanol and ethanol via the hydrogenation of cyclohexyl acetate with Cu2Znx/Al2O3 catalysts

The Cu2Zn1.25/Al2O3 catalyst exhibited 93.9% conversion and 97.2% selectivity to ethanol with 97.1% selectivity to cyclohexanol for the hydrogenation of cyclohexyl acetate due to the abundant weak acid sites and the highest ratio of Cu+/(Cu0 + Cu+).

Application of two morphologies of Mn2O3 for efficient catalytic ortho-methylation of 4-chlorophenol.

Vapor phase ortho-methylation of 4-chlorophenol with methanol was studied over Mn2O3 catalyst with two kinds of morphologies. Here, Mn2O3 was prepared by a precipitation and hydrothermal method, and showed the morphology of nanoparticles and nanowires, respectively. XRD characterization and BET results showed that, with the increase of calcination temperature, Mn2O3 had a higher crystallinity and a smaller specific surface area. N2 adsorption/desorption and TPD measurements indicated that Mn2O3 nanowires possessed larger external surface areas and more abundant acid and base sites. Simultaneously, in the fixed bed reactor, methanol was used as the methylation reagent for the ortho-methylation reaction of 4-chlorophenol. XRD, XPS, TG-MS and other characterizations made it clear that methanol reduced 4-chlorophenol and its methide, which were the main side-reactions. And Mn3+ was reduced to Mn2+ under the reaction conditions. Changing the carrier gas N2 to a H2/Ar mixture further verified that the hydrogen generated by the decomposition of methanol was not the reason for dechlorination of 4-chlorophenol compounds. Here we summarized the progress of 4-chlorophenol methylation based on the methylation of phenol. Also, we proposed a mechanism of the 4-chlorophenol dechlorination effect which was similar to the Meerwein–Ponndorf–Verley-type (MPV) reaction. The crystal phase and carbon deposition were investigated in different reaction periods by XRD and TG-DTA. The reaction conditions for the two kinds of morphologies of the Mn2O3 catalyst such as calcination temperature, reaction temperature, phenol–methanol ratio and reaction space velocity were optimized.

Slurry-Phase Hydrocracking of a Decalin–Phenanthrene Mixture by MoS2/SiO2–ZrO2 Bifunctional Catalysts

Slurry-phase hydrocracking is one of the most advanced technologies for the conversion of inferior heavy oil to light fuel oil. In this work, MoS₂ was combined with SiO₂–ZrO₂ mixed oxides to offer a new class of bifunctional catalysts for slurry-phase hydrocracking. In the bifunctional catalysts, SiO₂–ZrO₂ mixed oxides with abundant mesopores and acid sites act as cracking catalysts. They were presynthesized by a sol–gel-hydrothermal method and systematically characterized by X-ray diffraction (XRD), N₂ adsorption, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), NH₃-temperature programed desorption (NH₃-TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The effect of Si/Zr molar ratios on the chemical structure, especially the acid properties of SiO₂–ZrO₂ mixed oxides were examined. Subsequently, a mixture of decalin–phenanthrene was selected as the model system to investigate the performance of bifunctional catalysts. It was found that the conversions of decalin and phenanthrene were significantly improved for MoS₂/SiO₂–ZrO₂ bifunctional catalysts. Further analysis indicated that the Bronsted acid sites of SiO₂–ZrO₂ mixed oxides played an important role in the improvement of decalin and phenanthrene conversions.

Active sites adjustable phosphorus promoted CeO2/TiO2 catalysts for selective catalytic reduction of NOx by NH3

Highly-efficient CeO2-TiO2-based catalyst is an attractive alternative to traditional V2O5-based catalysts for selective catalytic reduction of NOx by NH3 (NH3-SCR). Herein, we construct an efficient and stable P-doped CeO2/TiO2 (yCeTi-Px) catalyst by dispersing CeO2 on strongly acidic and highly stable mesoporous P-doped TiO2 (Ti-Px). The characteristic structure of Ti-Px causes highly dispersed CeO2, strong active component-support interaction, and abundant surface active oxygen and acid sites on CeTi-P catalyst. Therefore, yCeTi-Px catalyst exhibits much higher catalytic activity than yCeTi catalyst at temperature of 200–450 °C. The yCeTi-Px catalysts show high activity in the presence of H2O and strong resistance to H2O + SO2 at medium-high temperature, implying that they have great industrial application prospects. Different P/Ti ratio and CeO2 loading content were investigated. Excessive P doping can block the Ce4+/Ce3+ redox couple, and suppress redox sites on yCeTi-Px catalyst. Additionally, increasing CeO2 content can reduce the NH3 capacity of yCeTi-Px catalyst. By controlling the P/Ti ratio and CeO2 loading content, surface acid sites and redox sites on yCeTi-Px catalyst can be balanced to obtain the best catalytic activity. This work demonstrates a feasible method in adjusting acid sites and redox sites on CeTi catalyst, which ultimately contributes to the new design of CeO2-TiO2-based catalyst.

One‐Pot Synthesized Nickel‐Doped Hierarchically Porous Beta Zeolite for Enhanced Methanol Electrocatalytic Oxidation Activity

AbstractHierarchically porous zeolites have been widely explored for catalytic applications owing to their high specific surface area, large pore volume, favorable mass transfer capability and abundant acidic sites. Herein we report the facile synthesis of Ni‐doped hierarchically Beta zeolite (Ni−H‐beta) via one‐pot hydrothermal method, in which Ni is uniformly doped into the zeolite crystalline skeleton in the form of Ni3+ without any nickel oxides being found. The prepared Ni−H‐beta zeolite shows high performance towards the electrocatalytic methanol oxidation reaction (MOR) with a high current density of 1450 A g−1 at 1.65 V vs RHE, which is higher than most non‐precious MOR electrocatalysts. More importantly, the electrochemical MOR performance has been identified to be closely related to the acidic property of the prepared samples. The increase in Al concentration resulted in the formation of strong acid sites, and the consequent MOR activity enhancement. These results provide valuable knowledge and favor the application of transition metals doped hierarchical zeolite for electrocatalytic MOR.

MOF-Assisted Synthesis of Highly Mesoporous Cr2O3/SiO2 Nanohybrids for Efficient Lewis-Acid-Catalyzed Reactions.

The facile fabrication of porous solid acids is highly desired for replacing hazardous liquid acids for many acid-catalyzed reactions in the industry. Herein, we present a bottom-up strategy to construct ultrastable mesoporous Cr2O3/SiO2 nanohybrids (denoted as Meso-Cr-Si-O) with highly dispersed Lewis acid sites by pyrolysis of a SiO2@MIL-101 precursor prepared via nanocasting by a reverse double-solvent approach, which can guarantee the efficient encapsulation of SiO2 nanoparticles (NPs) inside the MIL-101 pores. The pore environment of Meso-Cr-Si-O can be well tuned by simply controlling the amount of silica within the MIL-101 pores and the pyrolysis temperature. Pyridine adsorption experiments demonstrate that the density of Lewis acidic sites in the obtained Meso-Cr-Si-O is much higher than that of MIL-101-derived Cr2O3 NPs. Benefitting from its highly mesoporous nanostructure with abundant acid sites, the optimal Meso-Cr-Si-O exhibits a significantly improved catalytic activity for the Lewis-acid-catalyzed Meerwein-Ponndorf-Verley reduction of cyclohexanone with 4.5 times higher yield of cyclohexanol than that of the MIL-101-derived Cr2O3 NPs, representing the first efficient Cr2O3-based catalytic system for this reaction.

MnCO3-Catalyzed Transesterification of Alcohols with Dimethyl Carbonate Under Mild Conditions

Dimethyl carbonate (DMC) is a valuable green reagent with versatile and tunable chemical reactivity and can be used as a raw material for transesterification of alcohols. Herein, MnCO3 was found to be an efficient heterogeneous catalyst for transesterification of various alcohols with DMC and gave desired products under mild conditions. The MnCO3 catalysts were fully characterized by XRD, BET, SEM, TEM, FT-IR and NH3-TPD. The analysis results indicated that MnCO3 calcined at 300 °C has significantly enhanced surface area and abundant weak acid sites, which contributed to the superior catalytic performance in the transesterification. Furthermore, deactivation of catalyst resulted from the change of crystal structure and the decrease of weak acid sites. This research expands the potential application for DMC in green chemistry. In this work, MnCO3 was found to be an efficient heterogeneous catalyst for transesterification of various alcohols with DMC and gave desired products under mild conditions.

Synergetic catalytic removal of chlorobenzene and NOx from waste incineration exhaust over MnNb0.4Ce0.2Ox catalysts: Performance and mechanism study

Nb doped MnCe0.2Ox complex oxides catalysts prepared via a homogeneous precipitation method were investigated for synergistic catalytic removal of NOx and chlorobenzene (CB) at low temperatures. The MnNb0.4Ce0.2Ox catalyst with a molar ratio of Nb/Mn = 0.4 exhibits excellent activity and the NOx and CB removal efficiency reaches 94.5% and 96% at 220 °C, respectively. Furthermore, the NOx and CB removal efficiency of MnNb0.4Ce0.2Ox still remains above 80% after injecting 300 ppm SO2 and 7 vol% H2O for 36 h. In addition, the presence of CB and NOx + NH3 can improve the NOx and CB removal efficiency of MnNb0.4Ce0.2Ox, respectively. The analysis results from N2-BET, Py-IR, H2-TPR and NH3-TPD reveal that the introduction of Nb increases the average pore size, pore volume and surface area, promoted the growth of Lewis acid amount obviously, and enhances redox ability of MnCe0.2Ox at 100–250 °C. Moreover, the molecular migration process of NOx, NH3, CB and SO2 in NH3-SCR and CB oxidation reaction over MnNb0.4Ce0.2Ox catalysts were systematically studied. In situ DRIFTS, FT-IR and XPS also confirm that the adsorption of sulfate species and SO2 on the surface of MnNb0.4Ce0.2Ox is inhibited effectively by the introduction of Nb in the presence of SO2 and H2O. Moreover, Nb additives also enhance the structural stability of MnNb0.4Ce0.2Ox, due to the interactions among Mn, Nb and Ce. The NH3-TPD, H2-TPR and in situ DRIFTS results also confirm that the MnNb0.4Ce0.2Ox still retains abundant acid sites and high redox ability in the presence of SO2 and H2O. In summary, MnNb0.4Ce0.2Ox catalysts represent a promising and effective candidate for controlling NOx and CB at low temperatures.

A Cationic Oligomer as an Organic Template for Direct Synthesis of Aluminosilicate ITH Zeolite

There are a large number of zeolites, such as ITH, that cannot be prepared in the aluminosilicate form. Now, the successful synthesis of aluminosilicate ITH zeolite using a simple cationic oligomer as an organic template is presented. Key to the success is that the cationic oligomer has a strong complexation ability with aluminum species combined with a structural directing ability for the ITH structure similar to that of the conventional organic template. The aluminosilicate ITH zeolite has very high crystallinity, nanosheet-like crystal morphology, large surface area, fully four-coordinated Al species, and abundant acidic sites. Methanol-to-propylene (MTP) tests reveal that the Al-ITH zeolite shows much higher selectivity for propylene and longer lifetime than commercial ZSM-5. FCC tests show that Al-ITH zeolite is a good candidate as a shape-selective FCC additive for enhancing propylene and butylene selectivity.

A Cationic Oligomer as an Organic Template for Direct Synthesis of Aluminosilicate ITH Zeolite

AbstractThere are a large number of zeolites, such as ITH, that cannot be prepared in the aluminosilicate form. Now, the successful synthesis of aluminosilicate ITH zeolite using a simple cationic oligomer as an organic template is presented. Key to the success is that the cationic oligomer has a strong complexation ability with aluminum species combined with a structural directing ability for the ITH structure similar to that of the conventional organic template. The aluminosilicate ITH zeolite has very high crystallinity, nanosheet‐like crystal morphology, large surface area, fully four‐coordinated Al species, and abundant acidic sites. Methanol‐to‐propylene (MTP) tests reveal that the Al‐ITH zeolite shows much higher selectivity for propylene and longer lifetime than commercial ZSM‐5. FCC tests show that Al‐ITH zeolite is a good candidate as a shape‐selective FCC additive for enhancing propylene and butylene selectivity.

Alkali and Phosphorus Resistant Zeolite-like Catalysts for NOx Reduction by NH3.

At present, the deactivation of selective catalytic reduction (SCR) catalysts caused by the coexistence of alkali metal and phosphorus (P) remains an urgent problem and lacks corresponding strategies against catalyst poisoning. Herein, a novel zeolite-like Ce-Si5Al2Ox catalyst derived from an ultrasmall nanozeolite EMT precursor was synthesized without organic templates at ambient temperature. This catalyst was able to maintain above 95% NOx conversion in the 270-540 °C temperature range. Moreover, 1 wt % potassium (K) and 5 wt % P loading had no influence on the SCR performance of the Ce-Si5Al2Ox catalyst at 300-480 °C. It was demonstrated that cerium (Ce) was highly dispersed in the amorphous aluminum (Al) silicate derived from EMT zeolites and expressed high catalytic performance. Besides, a large number of acid sites were reserved to absorb ammonia allowing effective participation in the SCR reaction and capturing alkali metals, thus improving the SCR performance and K resistance. Additionally, the strong interaction between Ce and aluminosilicate decreased cerium phosphate production, preventing deactivation of the catalysts. Thus, this novel low-cost zeolite-like Ce-Si5Al2Ox catalyst with a highly active ion-exchanged metal phase and abundant surface acid sites paves a way for designing new efficient and poisoning-resistant SCR catalysts for practical applications.

Proton-exchanged montmorillonite-mediated reactions of hetero-benzyl acetates: Application to the synthesis of Zafirlukast

Proton-exchanged montmorillonite (H-mont) with outstanding surface characteristics can provide abundant acidic sites in the mesopores, and serve as an efficient heterogeneous catalyst for the synthesis of heterocycle-containing diarylmethanes via Friedel-Crafts-like alkylation of (hetero)arenes by heterobenzyl acetates under mild reaction conditions without requiring any additives or an inert atmosphere. Using this strategy, the gram-scale synthesis of indole-containing diarylmethane 13 has been accomplished in good yield for the preparation of Zafirlukast. In addition, H-mont can be applied to the nucleophilic substitution reactions of heterobenzyl acetate 5p with a variety of alcohols and 1,3-dicarbonyl compounds.

Competition between acidic sites and hydrogenation sites in Cu/ZrO2 catalysts with different crystal phases for conversion of biomass-derived organics

Oxides with different crystal phases can have important effects on the configuration of surface atoms, which can further affect the distribution of hydrogenation sites and acidic sites as well as the competitions of these varied types of catalytic sites. This could be potentially used to tailor the distribution of the products. In this study, zirconium oxides with different crystal phases supported copper catalysts were prepared for the hydrogenation of the biomass-derived furfural, vanillin, etc. The results showed that both calcination temperature and Cu species affected the shift of zirconia from tetragonal phase to the monoclinic phase. Monoclinic zirconia supported copper catalyst can effectively catalyze the hydrogenation of furfural to furfuryl alcohol via hydrogenation route due to its low amount of Brønsted acidic sites, although the surface area and the exposed metallic Cu surface area were much lower than the tetragonal zirconia supported copper catalyst. Zirconia with tetragonal or tetragonal/monoclinic phases supported copper catalysts contain abundant acidic sites and especially the Brønsted acidic sites, which catalyzed mainly the conversion of furfural via the acid-catalyzed routes such as the acetalization, rather than the hydrogenation. The acidic sites over the Cu/ZrO2 catalyst played more predominant roles than the hydrogenation sites in determining the conversion of the organics like furfural and vanillin.

Improvement of NH3 resistance over CuO/TiO2 catalysts for elemental mercury oxidation in a wide temperature range

In this study, the effects of ammonia (NH3) were explored for catalytic oxidation of elemental mercury (Hg0) over CeO2/TiO2, CuO/TiO2, Fe2O3/TiO2, and V2O5-WO3/TiO2 catalysts. In the presence of 50 ppm NH3, the results showed that CuO/TiO2 catalysts could still maintain 98–100 % of Hg0 conversion in the range of 100–400 °C, while the catalytic performance of other catalysts was significantly inhibited by NH3 in the same temperature range. NH3 resistance was observed on CuO/TiO2 catalysts. The catalysts were further characterized by means of XRD, H2-TPR, XPS, NH3-TPD, BET, and in-situ DRIFTS. For the CuO/TiO2 catalysts, Cu(II) was the primary Cu species that conducive to the strong reducibility properties which beneficial for the catalytic performance. The mechanism of NH3 resistance in Hg0 oxidation over CuO/TiO2 catalysts was proposed. At low-temperature range (lower than about 250 °C), abundant weak acidic sites contributed to the superior Hg0 adsorption capacity. The Hg0 oxidation activity was enhanced correspondingly. At high-temperature range (about 250–400 °C), the Hg0 oxidation performance was mainly affected by the oxidation of NH3 and the products. The main product of NH3 oxidation was NO2, which could promote Hg0 oxidation activity.

Continuous solvent-free synthesis of imines over uip-γ-Al2O3-CeO2 catalyst in a fixed bed reactor

One-pot synthesis of imines from benzyl alcohols and anilines by heterogeneous catalysis in batch reactor has already been widely studied, but its high cost and low production efficiency limit its application in the fine chemicals industry. In this work, γ-Al2O3 balls supported CeO2 catalyst (uip-γ-Al2O3-CeO2) was prepared by a novel unsaturated-impregnation-precipitation method, and was employed as a catalyst for continuous solvent-free synthesis of imines in a fixed bed reactor. Under the optimal technological parameter of fixed bed reactor and reaction condition, uip-γ-Al2O3-CeO2-500 °C obtained remarkable 97 % yield of imine. After 20 days` continuous operation, the total isolated yield of imine and TONBA/CeO2 reached up to 81 % and 16838, respectively. Importantly, the catalyst could be reactivated in situ in the fixed reactor. Through detailed characterization, the extraordinary catalytic performance of uip-γ-Al2O3-CeO2-500 °C can be attributed to the abundant acid sites of γ-Al2O3 as well as the synergistic effect between CeO2 and γ-Al2O3.

Hierarchical zeolites: synthesis, structural control, and catalytic applications

Zeolites possess unique ion exchange property, abundant acid sites, and highly hydrothermal stability, which have been widely used in catalysis, separation, and adsorption etc. However, the application of zeolite is greatly restrained in catalytic reactions involved in the large molecules due to their small micropore size (< 2 nm). Zeolites with hierarchically porous structure not only keep the crystalline framework, acidic sites, and highly hydrothermal stability but also improve diffusion of larger molecules. Thus, the catalyst life can be prolonged, which can expand their applications in the catalysis. In this review, the research progresses of hierarchical zeolites in terms of the controllable pore structural and synthetic strategy are summarized. Additionally, the applications of these hierarchical zeolites in catalysis are concluded. Furthermore, the hierarchical zeolites exhibit more excellent catalytic performance than conventional zeolite with sole micropores. Therefore, a perspective for promising application of the hierarchical zeolite in catalysis field is provided.