Higher Number Of Acid Sites Research Articles

The Effect of H2O2 Pretreatment on TiO2-Supported Ruthenium Catalysts for the Gas Phase Catalytic Combustion of Dichloromethane (CH2Cl2)

In the study presented herein, a series of TiO2-supported Ru catalysts were prepared through over-impregnation with different amounts of H2O2 and applied to the catalytic combustion of dichloromethane (DCM). The experimental results show that the optimal (1 H2O2)-Ru@TiO2 catalyst sample yields 90% DCM conversion at 301 °C, which is 40 °C lower than the temperature required by the (0 H2O2)-Ru@TiO2 catalyst. This good activity is related to its high number of acid sites (especially Brønsted acid sites), an appropriate amount of uniformly dispersed RuO2 particles, and strong interaction between RuO2 and the TiO2 support. In addition, excessive H2O2 leads to the growth and phase segregation of RuO2, which weakens the interaction between RuO2 and the TiO2 support and decreases catalytic activity. Moreover, H2O2 addition also contributes to the stability of catalysts, which possibly results from the re-dispersion of RuO2 on the TiO2 support during the reaction.

Catalytic Ozonation of Formaldehyde with an Oxygen-Vacancy-Rich MnOx/γ-Al2O3 Catalyst at Room Temperature

Formaldehyde (HCHO) is known as one of the important indoor organic pollutants. How to remove and decompose the low concentration of formaldehyde at room temperature is important for indoor environments. Catalytic ozonation is an efficient method to thoroughly remove HCHO at room temperature, with high efficiency and few byproducts. A series of MnOx/γ-Al2O3 catalysts were prepared in this work via the impregnation method and treated with different reagents (acid, alkali, and H2O2) to evaluate their catalytic activity for HCHO removal. The results showed that MnAl-II (acid treatment) performed well in activity tests, reaching a nearly 100% HCHO conversion at an O3/HCHO of 2.0 and attaining a CO2 selectivity of above 95% at an O3/HCHO of 3.0 at 30 °C, with almost no ozone residual existing. The larger specific surface area, abundant oxygen vacancies, and higher number of acid sites contributed to the excellent performance of MnAl-II. Stability and H2O resistance tests of MnAl-II were also conducted. To reveal the intermediate product formation and further investigate the reaction mechanism of HCHO ozonation, in-situ DRIFTS measurement was carried out combined with DFT calculations.

High‐Performance Supported Ru Catalysts for the Aqueous‐Phase Hydrogenation of Levulinic Acid to γ‐Valerolactone

Abstractγ‐Valerolactone (GVL) can be obtained by efficient hydrogenation of levulinic acid using ruthenium‐based catalysts in an aqueous medium. This paper reports an in‐depth study on the activity and selectivity of Ru catalysts supported on zirconia‐alumina, focusing on the effect of Ru concentration (0.5, 1.5 and 3 wt. % of Ru) and the selection of operational reaction variables. The results showed that the activity strongly depends on the number and oxidation state of the supported ruthenium particles. The most active catalyst, Ru3/ZA, presented the highest number of nanometric particles of zerovalent Ru and the highest number of acid sites. This catalyst gave ca. 100 % selectivity towards GVL, at high conversion of levulinic acid (over 99 %) under the best operating conditions evaluated (120 °C, 3 MPa H2 pressure, 1 h of reaction, and 0.1 g of catalyst). In addition, this catalyst kept high levels of conversion and selectivity after successive reuse cycles.

Green hydrogen production from ammonia water by liquid–plasma cracking on solid acid catalysts

In this study, a method for producing green hydrogen from ammonia water using plasma cracking was proposed. Solid acid catalysts, FAU and MFI zeolites, were used as catalysts. Zeolites were prepared by varying the Si/Al molar ratio to investigate the relationship between the acid sites of the catalyst and the reaction activity. The plasma was directly discharged into the ammonia water to generate hydrogen from the decomposition of ammonia. The gaseous products from the ammonia decomposition by plasma were mostly hydrogen with some nitrogen. No CO2 was produced. Even when the catalyst was not injected, approximately 100 L/h of hydrogen was produced only by plasma discharge. The injection of the FAU or MFI zeolite catalysts improved the hydrogen production rate. The rate of hydrogen production obtained from the decomposition of ammonia water by catalyst and plasma irradiation was the highest for the FAU zeolite with the highest number of acid sites. The hydrogen production rate tended to increase in proportion to the number of acid sites in the catalyst.

Mesostructured γ-Al2O3-Based Bifunctional Catalysts for Direct Synthesis of Dimethyl Ether from CO2

In this work, we propose two bifunctional nanocomposite catalysts based on acidic mesostructured γ-Al2O3 and a Cu/ZnO/ZrO2 redox phase. γ-Al2O3 was synthesized by an Evaporation-Induced Self-Assembly (EISA) method using two different templating agents (block copolymers Pluronic P123 and F127) and subsequently functionalized with the redox phase using an impregnation method modified with a self-combustion reaction. These nanocomposite catalysts and their corresponding mesostructured supports were characterized in terms of structural, textural, and morphological features as well as their acidic properties. The bifunctional catalysts were tested for the CO2-to-DME process, and their performances were compared with a physical mixture consisting of the most promising support as a dehydration catalyst together with the most common Cu-based commercial redox catalyst (CZA). The results highlight that the most appropriate Pluronic for the synthesis of γ-Al2O3 is P123; the use of this templating agent allows us to obtain a mesostructure with a smaller pore size and a higher number of acid sites. Furthermore, the corresponding composite catalyst shows a better dispersion of the redox phase and, consequently, a higher CO2 conversion. However, the incorporation of the redox phase into the porous structure of the acidic support (chemical mixing), favoring an intimate contact between the two phases, has detrimental effects on the dehydration performances due to the coverage of the acid sites with the redox nanophase. On the other hand, the strategy involving the physical mixing of the two phases, distinctly preserving the two catalytic functions, assures better performances.

Conversion of Multicyclic Hydrocarbons to Mono-Aromatic Hydrocarbons Over CoMo/Zeolite Socony Mobil-5 Catalysts.

This study focuses on analyzing the effects of the SiO₂/Al₂O₃ ratio of a support on the physico-chemical properties of bead-type CoMo/HZSM-5 catalysts and on the catalytic performance during the hydrocracking reaction of PFO. CoMo/HZSM-5 catalysts were prepared by an incipient wetness method. Subsequently, binder-added catalysts were molded into the bead type catalysts. The N2 adsorption-dersorption results clearly indicate that the nanoporous structure was well developed in the bead-type CoMo/HZSM-5 catalyst. The CoMo/HZSM-5(30) catalyst not only possessed the highest number of acid sites but also showed the highest ratio of strong acid to weak acid sites. Moreover, the Lewis acid/Brönsted acid site ratio is highest with the CoMo/HZSM-5(30) catalysts. A hydrocracking reaction of PFO over the bead-type CoMo/HZSM-5 catalysts was conducted at 400 °C and under 40 atm in a fixed-bed reactor. The bead-type CoMo/HZSM-5(30) catalyst showed the highest BTXE yield with a sum of BTXE outcome of 43.0% in the catalytic cracking reaction of PFO, which is attributed to the synergistic combination of suitable acidity and hierarchical porosity.

MOLYBDENUM SUPPORTED ON CARBON COVERED ALUMINA: ACTIVE SITES FOR n-BUTANOL DEHYDROGENATION AND KETONIZATION

For the work presented herein, molybdenum oxides supported on carbon coated alumina, were synthesized by precipitation of support and its impregnation with an aqueous solution of sucrose and ammonium molybdate. The effect of molybdenum content on the physico-chemical characteristics was investigated. The conversion of n-butanol depends on the concentration of acidic sites with medium and strong strength. The selectivity to 4-heptanone can be related to a good dispersion of molybdenum oxides (representing the active sites) on the surface. An increase in the size of the crystallites, evidenced by XRD, and the presence of phases corresponding to MoOxCy mixed oxides, leads to an increase in selectivity to butyraldehyde. The 10% molybdenum content represents the optimum value for the best conversion of n-butanol, at the same time obtaining the catalyst with the highest number of acid sites with strong strength.

A novel α-Fe2O3/AlOOH(γ-Al2O3) nanocatalyst for efficient biodiesel production from waste oil: Kinetic and thermal studies

Abstract Different α-Fe2O3 loading (4–12 wt%) doped nanowires AlOOH/γ-Al2O3 catalysts are synthesized using a deposition hydrothermal technique and thoroughly characterized using XRD, SAED-TEM, FTIR, UV–Vis, N2 sorptiometry and XPS measurements. The 12 wt% α-Fe2O3/AlOOH(γ-Al2O3) catalyst presented the highest fatty acid methyl ester (FAME) Yield that comprised of 100% for virgin oil and 94.3% for the waste one, all performed under mild optimized conditions (60 °C, methanol to oil molar ratio = 6:1, 3 wt% catalyst, reaction rate 600 rpm and within 3 h reaction time). It also shows high recyclability without significant loss in activity because of the superior large surface area (323.3 m2/g), high number of acid sites (0.45 mmol g−1), deep pore volume (0.322 ml/g) and to the exposed active site planes (110) and (214) of α-Fe2O3. The kinetic constant (k = 0.016–0.02 min−1) and the activation energy (Ea = 57.4 kJ mol−1) of the reaction together with ΔH ‡ (59.4 kJ mol−1), ΔG ‡ (+95.9 kJ mol−1) and ΔS ‡ (- 0.108 kJ mol−1) values elaborate that the reaction is endothermic, non-spontaneous and obey an associative path. The fuel properties derived from cottonseed oil exhibited high quality biodiesel comparable to the international (ASTM) standards.

Heterogeneous Bimetallic Cu–Ni Nanoparticle-Supported Catalysts in the Selective Oxidation of Benzyl Alcohol to Benzaldehyde

Three bimetallic Cu–Ni nanoparticle-supported catalysts were synthesized by co-immobilization followed by H2 reduction. A chromium(III) terephthalate metal organic framework (MIL-101), titanium dioxide (TiO2), and carbon (C) with different properties (acidity and Brunauer–Emmett–Teller surface area) were selected as supports for studying the effect of the support nature on the catalytic activity and selectivity in the oxidation of benzyl alcohol. The physicochemical properties of the Cu–Ni-supported catalysts were characterized by XRD, NH3-TPD, nitrogen adsorption/desorption, TEM, EDS, XPS, and ICP-OES. Bimetallic Cu–Ni nanoparticles were highly dispersed on the support. The catalytic activities of CuNi/MIL-101, CuNi/TiO2, and CuNi/C were tested in the selective oxidation of benzyl alcohol to benzaldehyde in the presence of molecular oxygen under mild reaction conditions. The highest benzaldehyde yields were achieved with CuNi/TiO2, CuNi/MIL-101, and CuNi/C catalysts at 100 °C within 4 h under 5, 3, and 3 bar of O2, respectively. The bimetallic Cu–Ni-supported catalysts possessed two types of catalytic active sites: acid sites and bimetallic Cu–Ni nanoparticles. The CuNi/MIL-101 catalyst possessed a high number of acid sites and exhibited high yield during selective benzyl alcohol oxidation to benzaldehyde. Importantly, the catalysts exhibited a high functional group (electron-donating and electron-withdrawing groups) tolerance. Cu–Ni-supported catalysts with an Cu:Ni mole ratio of 1:1 exhibited the highest yield of 47% for the selective oxidation of benzyl alcohol to benzaldehyde. Reusability and leaching experiment results exhibited that CuNi/MIL-101 showed better stability than CuNi/TiO2 and CuNi/C catalysts due to the large porous cavities of MIL-101 support; these cavities can be used to trap bimetallic Cu–Ni nanoparticles and inhibit nanoparticle leaching.

Hydroupgrading of Bio-Oil Over PtMg/KIT-6 Catalysts.

The objective of this study is to evaluate the catalytic potential of PtMg/Al-KIT-6 during the hydroupgrading of a mixture composed of C15-C18 alkane as a model compound of bio-oil obtained by a hydrodeoxygenation of palm oil. Al-KIT-6 was prepared through a post-alumination method using KIT-6, after which platinum and magnesium precursors were impregnated onto the synthesized Al-KIT-6. PtMg/Al-KIT-6 catalysts were shown to have a well-arranged mesoporous structure, a large surface area, and a large pore size. The jet-fuel yield (55-59%) in the hydroupgrading of the long-chain n-alkane mixture over PtMg/Al-KIT-6 catalysts was much higher than that over the PtMg/KIT-6 catalyst, which could be ascribed to the higher number of acid sites of the PtMg/Al-KIT-6 catalysts. The highest isomer selectivity of the PtMg/Al-KIT-6(20) catalyst can be attributed to the strong acidity as well as the abundance of acid sites. PtMg/Al-KIT-6 catalysts can be effective catalysts for producing jet fuel through the hydroupgrading of bio-oil.

Magnetically recyclable acidic polymeric ionic liquids decorated with hydrophobic regulators as highly efficient and stable catalysts for biodiesel production

Biodiesel, typically produced from non-food crops with heterogeneous catalysts, deems to be a promising and sustainable alternative biofuel to petroleum-derived fuels. In this study, to improve biodiesel production process efficiency by acids, biodiesel production were successfully developed using a series of magnetically acidic poly(ionic liquid) catalysts with varying hydrophobicity and controllable acidity. The detailed characterization results demonstrated that the FnmS-PIL (1a, C8) core-shell structure catalyst had large Bruner Emmett and Teller (BET) surface area (128.1 m2/g), uniform mesoporous structure (4.2 nm), strong magnetism (12.4 emu/g), a high number of acid sites (2.14 mmol/g), strong acid strength (strong electron-withdrawing anion CF3SO3− effect, −8.2 < H0 < −5.6) and strong hydrophobicity (water contact angle, 115.4°). For the biodiesel production, high biodiesel yields could be achieved by the esterification of oleic acid (by response surface methodology, RSM) and (trans)esterification of crude Euphorbia lathyris L. oils with an acid value of 24.59 mg KOH/g (by single factor optimization). Furthermore, a relative kinetic study was conducted wherein the activation energy was calculated as 39.2 kJ/mol and a pseudo-first-order model was determined for esterification. More importantly, the FnmS-PIL (1a, C8) catalyst was separated simply using a magnet and exhibited constant activity with biodiesel yield of 87.5% after five cycles in (trans)esterification. In addition, the biodiesel yield was maintained above 90% even with a water content of 6 wt% with respect to crude Euphorbia lathyris L. oils, and the fuel properties of Euphorbia lathyris L. biodiesel were found to satisfy the EN 14212 and ASTM D6751 standards, highlighting its potential in industrial biodiesel production as derived from crude non-food oil resources.

Strategies of Coping with Deactivation of NH3-SCR Catalysts Due to Biomass Firing

Firing of biomass can lead to rapid deactivation of the vanadia-based NH3-SCR catalyst, which reduces NOx to harmless N2. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K2SO4. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K+ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO3 with heteropoly acids, and by preparing highly loaded, high surface area, very active V2O5/TiO2 catalyst using a special sol-gel method.

Microwave-assisted etherification of glycerol with tert-butyl alcohol over amorphous organosilica-aluminum phosphates

The synthesis of organosilica-aluminum phosphates by a simple and cheap sol-gel method was carried out with varying amounts of two different silica precursors, 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (C) and (3-mercaptopropyl)trimethoxysilane (MPTMS); and several Al/P molar ratios. The solids were calcined in air, at different temperatures. The etherification of glycerol with tert-butyl alcohol was carried out in the liquid-phase under microwave irradiation and also by conventional heating. The incorporation of organosilica in the final solids took place in a 50–60%, as verified by TGA, ICP-MS, XPS and 1H–29Si CP MAS NMR. The highest yield to h-GTBE (21%) was obtained at autogenous pressure, 85°C and 15min of reaction time under microwave, on the solid prepared with 10mmol of C; Al/P=1.5 and calcined at 250°C. This material, with a balanced percentage of mesopores and macropores, also exhibited the highest number of acid sites determined by acid-base titration, as well as by results from TGA and by elemental analysis. The acidity and the hydrophilic character of the solids have been found to be key parameters for the catalytic activity, whereas porosity seems to be advantageous for the reusability of the solids, avoiding deactivation.

Rare earth ions (La, Nd, Sm, Gd, and Tm) regulate the catalytic performance of CeO2/Al2O3 for NH3-SCR of NO

Abstract

Promoted V2O5/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperatures

The influence of varying the V2O5 content (3–6wt.%) was studied for the selective catalytic reduction (SCR) of nitrogen oxides by ammonia on heteropoly acid (HPA)- and tungsten oxide (WO3)-promoted V2O5/TiO2 catalysts. The SCR activity and alkali deactivation resistance of HPA-promoted V2O5/TiO2 catalysts was found to be much higher than for WO3- promoted catalysts. By increasing the vanadium content from 3 to 5wt.% the catalysts displayed a two fold increase in activity at 225°C and retained their initial activity after alkali doping at a molar K/V ratio of 0.181. Furthermore, the catalysts were characterized by N2 physisorption, XRPD, NH3-TPD, H2-TPR, Raman, FTIR and EPR spectroscopy to investigate the properties of the catalysts. XRPD, Raman and FTIR showed that promotion with 15wt.% HPA does not cause V2O5 to be present in crystalline form, also at a loading of 5wt.% V2O5. Hence, use of HPAs does not cause increased N2O formation or unselective oxidation of NH3. NH3-TPD showed that promotion by HPA instead of WO3 causes the catalysts to possess a higher number of acid sites, both in fresh and alkali poisoned form, which might explain their higher potassium tolerance. Ex-situ EPR spectroscopy revealed that HPA-promoted catalysts have higher V4+/Vtotal ratios than their WO3-promoted counterparts. H2-TPR suggests that HPAs do not have a beneficial effect on the V5+-V3+ redox system, relative to WO3.

Effect of the plasma-chemical treatment of ZnO and NiO on their activity in the dehydrogenation of isopropanol

Treating ZnO and NiO oxides with glow discharge oxygen plasma and high-frequency argon plasma is found to affect the catalytic activity of these oxides in the dehydrogenation reaction of isopropanol, leading to an increase in the conversion of alcohol and the yield of acetone. The increased activity of ZnO is due to the high number of acid sites induced by plasma-chemical treatment. With NiO, the increased activity results from the formation of new, more active sites with low experimental activation energy, rather than a change in the surface acidity.

Study on the catalytic conversion of lignin-derived components in pyrolysis vapour using model component

Vanillyl alcohol was chosen as a model component for lignin-derived components in bio-oil. The catalytic conversion of vanillyl alcohol over different catalysts was studied and it has been shown that this model component has undergone consecutive reactions to form methoxy phenols, phenols, and eventually hydrocarbons with increasing degree of de-oxygenation. The degree of de-oxygenation of vanillyl alcohol was shown to increase with the increase in number of acid sites in catalysts. γ-Al2O3 material with the highest number of acid sites has resulted in the highest yield of aromatic hydrocarbons, accompanied by the highest yields of coke and gas compared to other materials used in this study. Two pathways have been shown leading to the formation of hydrocarbons from vanillyl alcohol, which are: (i) decomposition of vanillyl alcohol into small olefinic hydrocarbon fragments and the subsequent aromatisation into final products and (ii) direct de-oxygenation of this model component over catalysts.

Heterogeneous catalyst-assisted thermochemical conversion of food waste biomass into 5-hydroxymethylfurfural

A novel thermochemical conversion route has been developed that yields 5-hydroxymethylfurfural (HMF) from food waste biomass (FWB) in the presence of a heterogeneous catalysts (zirconium phosphate (ZrP)). The ZrP catalyst was prepared by precipitation followed by calcination at 400 (ZrP-400) and 600°C (ZrP-600) and was characterized by SEM, XRD, XPS, N2 sorption and NH3-TPD. The optimized reaction conditions were identified to maximize HMF yield by varying the type of catalyst, the catalyst loading and the reaction time. The highest HMF yield achieved was 4.3%. On average 33% higher yield for ZrP-600 was obtained compared to that for ZrP-400, which might be due to higher number of acid sites on ZrP-600. The ZrP catalyst was easily regenerated by thermal treatment and showed stable activity upon its reuse. Preliminary calculations of the “minimum selling price” of HMF suggest that it is economically attractive to make this industrially-relevant chemical from FWB.

Effect of TiO2 calcination temperature on the photocatalytic oxidation of gaseous NH3

Carbon-modified titanium dioxide (TiO2) was prepared by a sol-gel method using tetrabutyl titanate as precursor, with calcination at various temperatures, and tested for the photocatalytic oxidation (PCO) of gaseous NH3 under visible and UV light. The test results showed that no samples had visible light activity, while the TiO2 calcined at 400°C had the best UV light activity among the series of catalysts, and was even much better than the commercial catalyst P25. The catalysts were then characterized by X-ray diffractometry, Brunauer-Emmett-Teller adsorption analysis, Raman spectroscopy, thermogravimetry/differential scanning calorimetry coupled with mass spectrometry, ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy. It was shown that the carbon species residuals on the catalyst surfaces induced the visible light adsorption of the samples calcined in the low temperature range (< 300°C). However, the surface acid sites played a determining role in the PCO of NH3 under visible and UV light over the series of catalysts. Although the samples calcined at low temperatures had very high SSA, good crystallinity, strong visible light absorption and also low PL emission intensity, they showed very low PCO activity due to their very low number of acid sites for NH3 adsorption and activation. The TiO2 sample calcined at 400°C contained the highest number of acid sites among the series of catalysts, therefore showing the highest performance for the PCO of NH3 under UV light.

Characteristics of pellet-type adsorbents prepared from water treatment sludge and their effect on trimethylamine removal

We optimized the preparation method of pellet-type adsorbents based on alum sludge with the aim of de- veloping a high-performance material for the adsorption of gaseous trimethylamine. Effects of calcination tempera- ture on physical and chemical properties of pellet-type adsorbents were investigated. The porous structure and surface characteristics of the adsorbents were studied using N2 adsorption and desorption isotherms, scanning electron micro- scope, X-ray diffraction, temperature-programmed desorption of ammonia, and infrared spectroscopy of adsorbed pyr- idine. The adsorbents obtained from the water treatment sludge are microporous materials with well-developed mesopo- rosity. The pellet-type adsorbent calcined at 500 o C had the highest percentage of micropore volume and the smallest average pore diameter. The highest adsorption capacity in trimethylamine removal attained over the pellet-type adsorbent calcined at 500 o C can be attributed to the highest number of acid sites as well as the well-developed microporosity.