α-Al2O3 Catalyst Research Articles

Exothermic characteristics evaluation of the Pt coated α-Al2O3 catalyst in bed for passive airborne radioactive material reduction system under forced flow conditions

After the severe accident at the Fukushima nuclear power plant, there has been heightened interest in the development of severe accident countermeasures. As part of these efforts, a passive filtration system capable of passive operation during power loss is under development.This paper focuses on evaluating the performance of a catalyst-filled bed designed to create a temperature gradient through exothermic reactions between combustible gases generated during accidents and a catalyst. The temperature gradient facilitates the formation of natural convection within the system, enabling passive operation. The catalytic bed is designed in a bed-type configuration filled with exothermic catalysts. To ensure physical and chemical stability under severe accident conditions, heat resistance tests were conducted using inorganic materials as a base to select an optimized exothermic catalyst. A test apparatus was designed for unit evaluation testing of the catalyst-filled bed equipped with the catalytic bed. Exothermic characteristics evaluation tests were conducted by varying the hydrogen volume fraction and face velocity, measuring heat generation in the catalytic bed under each condition. The correlation between these variables and the heat generation performance of the catalytic bed was determined. These findings will be utilized to inform the design parameters of the passive airborne radioactive material reduction system.

Tailoring the Brønsted acidity of Ti-OH species by regulating Pt-TiO2 interaction.

Bifunctional catalysts comprising metal and acid sites are commonly used for many reactions. Interfacial acid sites impact intermediate reactions more than other sites. However, controlling the type and amounts of interfacial acid sites by regulating metal-support interaction (MSI) via traditional methods is difficult. Thus, the influence of MSI on interfacial acid sites remains unclear. We prepared Pt-mTiO2/α-Al2O3 (m represents the cycle number of TiO2) catalysts via atomic layer deposition (ALD). New Brønsted acid sites were generated via Pt-TiO2 interaction, and the acidity was precisely regulated by regulating Pt-TiO2 interaction by changing the TiO2 nanolayer thickness. We chose levulinic acid (LA) hydrogenation as a model reaction. The catalytic activity varied with the TiO2 nanolayer thickness and was linearly correlated with the Ti-OH species (Brønsted acid) content. Pt-40TiO2/α-Al2O3, with the highest acid site content of 0.486 mmol/g, exhibited the best catalytic activity. Hydrogen spillover and water dissociation at the Pt-TiO2 interface promoted Ti-OH species generation.

Creation of a Highly Active Small Cu-Based Catalyst Derived from Copper Aluminium Layered Double Hydroxide Supported on α-Al2 O3 for Acceptorless Alcohol Dehydrogenation.

A highly dispersed carbonate-intercalated Cu2+ -Al3+ layered double hydroxide (CuAl LDH) was created on an unreactive α-Al2 O3 surface (CuAl LDH@α-Al2 O3 ) via a simple coprecipitation method of Cu2+ and Al3+ under alkaline conditions in the presence of α-Al2 O3 . A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl2 O4 on the surface of α-Al2 O3 (CuAlO@α-Al2 O3 ) after calcination at 1073 K in air, as confirmed by powder X-ray diffraction (XRD) and Cu K-edge X-ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in-situ temperature-programmed synchrotron XRD (tp-SXRD). The layered structure of CuAl LDH@α-Al2 O3 completely disappeared at 473 K, and CuO or CuAl2 O4 phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α-Al2 O3 catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1-phenylethanol dehydrogenation. The results suggested that Cu0 was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species.

Oxidative coupling of biogas to ethylene over a trilobe-shaped Mn-Na2WO4/α-Al2O3 catalyst in a single-pellet reactor

Despite the development of selective catalyst formulations for oxidative coupling of methane (OCM), kinetic and reactor design studies have been hampered by a lack of data for truly isothermal reaction conditions. Because of the high exothermicity, the temperature of a fixed-bed reactor filled with Mn-Na2WO4/SiO2 catalysts will show hot-spots with a loss of selectivity. The objective of this study is to measure catalyst activity under relevant reaction conditions of pressure (3 bar), biogas composition (no dilution) and contact time, while keeping the process isothermal. To this aim, we have synthesized and shaped a trilobed Mn-Na2WO4/α-Al2O3 catalyst, which may be used as is at industrial scale, and measured its performance in a single-pellet reactor. We found that the presence of CO2 did not degrade the catalyst performance, even on the long run, which should enable the use of a CO2-rich stream such as biogas. Actually, higher methane conversions have been obtained in the presence of CO2, likely due to a possible contribution of methane dry reforming reaction. We also noticed a slow catalyst activation over the first 100 h, while selectivity was kept constant.

Modifying α-Al2O3 with cerium, zirconium, and sulfate for catalytic removal of C4F8.

Modification of α-Al2O3 (A) with cerium (C), zirconium (Z), and sulfate (S) for effective C4F8 removal is evaluated at temperatures ≤ 650°C. Catalytic hydrolysis of C4F8 is conducted to compare the performance of catalysts prepared (namely, A, AC, AZ, AS, ACS, and AZS). The interplay between rare earth element, acid amount, and surface area is further investigated. An investigation was carried out by characterization of catalysts by using XRD, BET, and NH3-TPD. XRD pattern of the modified α-Al2O3 catalyst shows that the average grain size is 37nm. BET analysis indicates that the surface area increases with the addition of Ce and Zr, while NH3-TPD analysis shows the improvement of acid sites after the addition of Ce, Zr, and SO42-. The experimental results indicate that C4F8 conversion over A catalyst reaches 14.81% at 550°C with the addition of 38% H2O(g). Under the same operating condition, C4F8 conversion efficiencies achieved with AC and AZ catalysts increase to 42.03% and 50.1%, respectively. Furthermore, the efficiencies over AS, ACS, and AZS catalysts increase to 49.85%, 86.94%, and 87.18%, respectively. Stability tests show that the performances of the catalysts for C4F8 conversion are with the order of AZS > ACS > AZ > AC > AS > A at 650°C during 24h. The activation energy of the AZS catalyst in catalytic hydrolysis of C4F8 is 60.49kJ/mol. The products of C4F8 conversion mainly include CO2, CO, and COF2 and small amounts of CHF3 and C2F4. This study has confirmed that the AZS catalyst shows the best activity, acidity, and stability on C4F8 removal.

Morphologically tailored facet dependent silver nanoparticles supported α-Al2O3 catalysts for chemoselective reduction of aromatic nitro compounds

The nanoparticles surface area, intrinsic sites, exposed microcrystal shapes and lattice planes are some of the key factors in nanocatalysis. The influence of nanoparticles shape dependent had been profound effect on its catalytic activity. This study is focused on the synthesis of morphologically shape-controlled silver (Ag) nanoparticles supported on α-Al2O3 catalysts were performed. The correlation of Ag NPs with varied facets and lattice planes on the catalytic activities in chemoselective reduction of nitro compounds was investigated. Engineering the silver nanoparticles with different shapes and facets i.e., nanocubes (AgNCs), nanowires (AgNWs) and nano spheres (AgNSPs) were synthesized by using modified polyol method. It is demonstrated that there is a significant difference in their activities with respect to the shape and nanocrystal facets. The evolution of nanoshapes and the structural properties of Ag nanoparticles were analysed by SEM, TEM, HR-TEM and P-XRD techniques. From XRD, Ag nanocubes exhibited high percentage of low index (100) facets which are favourable active centers than (111) plane in nitro reduction. We observed that the silver nanocubes selectively exposed (100) facets, which are highly favorable for the enhanced catalytic activity in nitro reduction. The reaction rate of nitro phenol to amino phenol over different Ag nanoshapes are 35.01 × 10−3 min−1 (AgNCs/Al2O3), 8.28 × 10−3 min−1 (AgNWs/Al2O3), 0.65 × 10−3 min−1 (AgNSPs/Al2O3), respectively. The calculated thermodynamic parameters of the Ea values 23.6, 28.6 and 29.4 for the AgNC, AgNWs and AgNSP respectively.

Morphologically Tailored Facet Dependent Silver Nanoparticles Supported Α-Al2o3 Catalysts for Chemoselective Reduction of Aromatic Nitro Compounds

Morphologically Tailored Facet Dependent Silver Nanoparticles Supported Α-Al2o3 Catalysts for Chemoselective Reduction of Aromatic Nitro Compounds

Optimization of the potassium promotion of the Co|α-Al2O3 catalyst for the effective hydrogen production via ethanol steam reforming

A series of K-Co|α-Al2O3 catalysts doped with potassium in the range of 0–4 wt% were synthesized and studied in the ethanol steam reforming process. The enhancement of activity and selectivity of the Co|α-Al2O3 catalyst upon the K doping was explained by potassium impact on the reducibility of the cobalt oxide precursor and acidity of the catalyst: K promotor inhibited the cobalt reduction and substantially increased the number of strong Lewis sites. The investigations of the surface state of potassium using a species resolved thermal alkali desorption method allowed for defining optimal potassium dispersion accurately, corresponding to the concentration of 0.3 wt%. Samples with higher potassium contents due to the overloading did not exhibit any improvement of the catalyst efficiency. Presented studies revealed the key importance of the precise optimization of the K loading and dispersion on the Co|α-Al2O3 catalyst for efficient hydrogen production via the ethanol steam reforming process.

Cobalt catalyst for steam reforming of ethanol–Insights into the promotional role of potassium

The promotional effect of potassium doping on the ESR performance of the CoZn|α-Al2O3 catalyst was thoroughly investigated in the context of its impact on the selectivity and stability of the catalyst, and discussed in terms of cobalt dispersion, oxidation state, cobalt-alumina interactions, catalyst acidity, and the deactivation resistance of the catalyst. The potassium slightly inhibited the cobalt reducibility (XPS, TPR, STEM/EELS), significantly increased the surface concentration and the strength of Lewis sites (FT-IR), enhancing the selectivity to hydrogen. The surface state of potassium at various stages of the catalyst evolution was examined with a species resolved thermal alkali desorption (SR-TAD) method. These studies revealed a pronounced migration of K from the cobalt nanograins towards the alumina support upon the activation and during the ESR processes. Potassium stabilizes the high dispersion of cobalt crystallites and prevents their detachment from the surface and subsequent encapsulation by the growing carbon deposit.

MgxAl-LDHs layered double hydroxides catalysts for boosting catalytic synthesis of biodiesel and conversion of by-product into valuable glycerol carbonate

Abstract A series of layered double hydroxides (MgxAl-LDHs) catalysts is successfully prepared and effectively transesterificated triglycerides to produce biodiesel and glycerol carbonate, respectively. MgxAl-LDHs catalysts are synthesized by changing the Mg/Al ratio of the LDH hosts and fully characterized by several techniques, including XRD, N2 adsorption, SEM. The effects of ratios of Mg/Al catalyst, reaction temperature, catalyst dosage are thoroughly investigated to determine the optimal reaction conditions. A yield of biodiesel and glycerol carbonate could reach up to 87.5% and 93.4%, respectively, over Mg5Al-LDHs catalyst under batch condition. The transesterification glycerol for glycerol carbonate is successfully carried out in a stirring packed-bed reactor with MgxAl-LDHs coating on the spherical α-Al2O3 catalysts. Additionally, extra-particle mass transfer and intra-particle diffusion do not control the reaction rate. The yield of glycerol carbonate could reach up to 80.2% over Mg5Al-LDHs/α-Al2O3 catalyst.

Origin and Nature of Coke in Ethanol Steam Reforming and Its Role in Deactivation of Ni/La2O3–αAl2O3 Catalyst

Deactivation of Ni/La2O3–αAl2O3 catalyst in ethanol steam reforming (ESR) was studied in order to establish the optimal conditions for maximizing H2 production and achieving steady behavior. The ES...

An Experimental Approach on Industrial Pd-Ag Supported α-Al2O3 Catalyst Used in Acetylene Hydrogenation Process: Mechanism, Kinetic and Catalyst Decay

The current research presents an experimental approach on the mechanism, kinetic and decay of industrial Pd-Ag supported α-Al2O3 catalyst used in the acetylene hydrogenation process. In the first step, the fresh and deactivated hydrogenation catalysts are characterized by XRD, BET (Brunauer–Emmett–Teller), SEM, TEM, and DTG analyses. The XRD results show that the dispersed palladium particles on the support surface experience an agglomeration during the reaction run time and mean particle size approaches from 6.2 nm to 11.5 nm. In the second step, the performance of Pd-Ag supported α-Al2O3 catalyst is investigated in a differential reactor in a wide range of hydrogen to acetylene ratio, temperature, gas hourly space velocity and pressure. The full factorial design method is used to determine the experiments. Based on the experimental results ethylene, ethane, butene, and 1,3-butadiene are produced through the acetylene hydrogenation. In the third step, a detailed reaction network is proposed based on the measured compounds in the product and the corresponding kinetic model is developed, based on the Langmuir-Hinshelwood-Hougen-Watson approach. The coefficients of the proposed kinetic model are calculated based on experimental data. Finally, based on the developed kinetic model and plant data, a decay model is proposed to predict catalyst activity and the parameters of the activity model are calculated. The results show that the coke build-up and condensation of heavy compounds on the surface cause catalyst deactivation at low temperature.

Synthesis and characterization of a La Ni/α-Al2O3 catalyst and its use in pyrolysis of glycerol to syngas

Abstract The current paper reports on the kinetics of syngas production from glycerol catalytic pyrolysis over Ni/α-Al2O3 catalyst promoted by lanthanum. The 3 wt%La-20 wt%Ni/77 wt%α-Al2O3 catalyst was synthesized and its physiochemical properties were characterized. The BET specific surface area was 2.20 m2.g−1, which was 0.11 m2.g−1 larger than the unpromoted Ni/α-Al2O3 catalyst. Significantly, the BET results were supported by the FESEM image which showed that the promoted catalyst has smaller particle size compared to the unpromoted catalyst. The NH3 and CO2-TPD analyses indicates that the catalyst has net acidity with acid:base ratio of 1.12. Catalytic pyrolysis was performed in a 10 mm-ID stainless steel fixed bed reactor with reaction temperatures set at 973, 1023 and 1073 K, employing a weight-hourly-space-velocity (WHSV) of 4.5 × 104 ml g−1 h−1. From reaction studies, the highest glycerol conversion (XG) value was 36.96% at 1073 K. The resulting syngas has H2:CO ratios always lower than 2.0. Subsequently, mechanistic studies indicate that the catalytic glycerol pyrolysis occurred on single catalytic site via associative adsorption, with molecular surface reaction as the rate-determining step.

Temperature Programmed Oxidation Coupled with In Situ Techniques Reveal the Nature and Location of Coke Deposited on a Ni/La2O3‐αAl2O3 Catalyst in the Steam Reforming of Bio‐oil

AbstractThe characterization of coke deposited on a Ni/La2O3‐αAl2O3 catalyst used in the steam reforming of bio‐oil has been studied by temperature programmed oxidation (TPO) coupled with different in situ techniques: thermogravimetry (TG), modulated thermogravimetry (MTG), FTIR spectroscopy with mass spectrometry (MS), Raman spectroscopy, and differential scanning calorimetry (DSC). The steam reforming of bio‐oil was carried out in a reactor equipment with two steps in series, comprising bio‐oil thermal treatment (500 °C) and subsequent reforming in a fluidized bed reactor (550–700 °C; and steam‐to‐carbon ratio, 1.5–6). TG/MS‐TPO experiments identify encapsulating and filamentous coke, and a more detailed analysis using other in situ techniques enable to characterize the nature and location of 4 types of coke: (i) an encapsulating coke with aliphatic nature placed in the most superficial layers; (ii) an encapsulating coke with higher aromatic nature in inner layers; (iii) the most superficial layers of a filamentous coke, further from active sites and with a more carbonized structure compared to encapsulating coke; and (iv) an innermost and mainly polyaromatic filamentous coke with a low oxygenates content.

Catalytic pyrolysis of glycerol into syngas over ceria-promoted Ni/α-Al2O3 catalyst

This paper reports on the catalytic pyrolysis of glycerol into syngas over a 3 wt%Ce-20 wt%Ni/77 wt% α-Al2O3 catalyst and at reaction temperatures of 973 K, 1023 K and 1073 K. NH3- and CO2-TPD analyses have revealed that the as-synthesized catalyst was net acidic with acid-to-basic site ratio of 1.24. This provides ideal conditions for chemisorption of glycerol. In addition, the BET specific surface area was 2.89 m2 g−1. The small surface area can be attributed to the thermally stable α-Al2O3 support. In addition, the average crystallite size was 40.22 nm. The catalytic glycerol pyrolysis produced gaseous products that were comprised of H2, CO, CO2 and CH4 only with H2:CO ratios that were consistently less than 2.0. This ratio is suitable for Fischer-Tropsch synthesis. The yields of CO2 and CH4 were several folds lower than the yields of H2 and CO, indicating that the latter were from primary reaction, viz. glycerol decomposition whilst the former were from secondary competing reactions. In addition, the activation energy obtained via Langmuir-Hinshelwood model was 25.34 kJ mol−1. Used catalyst characterization showed that the carbonaceous deposit was in the forms of whisker-type. This type of carbon deposit would not physically deactivate the catalyst.

Thermal stability and repartition of potassium promoter between the support and active phase in the K-Co2.6Zn0.4O4|α-Al2O3 catalyst for N2O decomposition: Crucial role of activation temperature on catalytic performance

The effect of calcination temperature of potassium promoted cobalt spinel catalyst supported on α-alumina extrudates was investigated for understanding its diverge role in N2O decomposition. The catalyst were thoroughly characterized by XRD, μRS, IR, XPS, X-ray μ-tomography, SEM, STEM-EDX techniques. Potassium stability and surface location were evaluated by species resolved thermal alkali desorption (SR-TAD). It was found that the potassium promoter is unevenly distributed between the spinel active phase and the support, due to different energetic stability of 2.4-2.6eV and 1.7eV, respectively. Strong beneficial influence of the K-dopant on the catalyst activity, observed for the catalysts calcined at 500°C, substantially attenuated upon increasing the calcination temperature above 600°C. It was accounted for by the migration of potassium from the support to the spinel nanocrystals (below 500°C) and subsequent formation of potassium cobaltate overlayer (above 600°C). Thus while the support is acting as a potassium reservoir, the spinel active phase acts as a potassium sink. The presence of the cobaltate shell around the spinel nanocrystallites was revealed by FTIR and SR-TAD techniques, and corroborated by STEM-EDX elemental mapping. The results point out that in the case of the supported cobalt spinel catalysts promoted by alkali careful selection of the proper activation conditions is crucial for their optimal performance.

An efficient and recyclable 3D printed α-Al2O3 catalyst for the multicomponent assembly of bioactive heterocycles

A catalytic methodology is reported that enables the efficient, operationally simple and environmentally friendly synthesis of diverse 1,4-dihydropyridines and 3,4-dihydropyrimidin-2(1H)-ones, including some relevant drugs and pharmacologically active derivatives. This strategy is based on the use of a 3D printed Al2O3 woodpile material that was sintered to generate a rigid structure with controlled porosity and noteworthy catalytic performance. The 3D printed Al2O3 catalyst exhibits remarkable efficacy as a Lewis acid in Biginelli and Hantzsch reactions and it can be recovered and reused ten times without any decrease in the activity. Remarkable E factors, excellent recyclability and scalability, broad substrate scope, short reaction times, excellent yields, solvent-free conditions and easy isolation procedures are key features of this methodology.

An Effective Strategy to Prepare Pd–Ag/MgCO3@α-Al2O3 Catalyst for Selective Hydrogenation of Acetylene

A spherical Pd-Ag/MgCO3@alpha-Al2O3 catalyst with highly stable dispersion has been designed and synthesized by an effective in-situ synthetic approach for selective hydrogenation of acetylene. MgCO3 was synthesized in-situ on the surface of spherical alpha-Al2O3 to obtain MgCO3@alpha-Al2O3 support, followed by the introduction of Pd(NO3)(2) and AgNO3. Importing MgCO3 structure offers larger specific surface area to realize uniform dispersion of active constituent Pd, moreover, the synthesized support exhibited the effects on modification of Pd electronic structure and the surface acidity of catalyst. With this Pd-Ag/MgCO3@alpha-Al2O3 catalyst (cat-48) at 70 A degrees C (industrial reaction temperature), acetylene conversion, ethylene selectivity, MAPD conversion, propylene selectivity and n-butene formed can reach 89, 92, 28, 96% and 124 ppm, respectively. In addition, during 500 h long-term test, conversion and selective behaviors of Pd-Ag/MgCO3@alpha-Al2O3 catalyst can basically remain stable. All this catalytic efficiency parameters are superior to Pd-Ag@alpha-Al2O3 (most commonly used in industrial) and Pd-Ag/MgAl-LDH@alpha-Al2O3. We believe that the Pd-Ag/MgCO3@alpha-Al2O3 catalyst with high dispersion of Pd and synergistic effects could be a highly efficient industrial catalyst for selective hydrogenation of acetylene to ethylene. [GRAPHICS] .

Renewable syngas production from thermal cracking of glycerol over praseodymium-promoted Ni/Al2O3 catalyst

In this study, the kinetics of glycerol pyrolysis over a 3wt%Pr-20wt%Ni/77wt%α-Al2O3 catalyst was investigated. The catalyst was synthesized via wet-impregnation method and was characterized using temperature-programmed calcination (TPC), temperature-programmed reduction (TPR), N2-physisorption, FESEM imaging, X-ray diffraction and CO2-/NH3-temperature-programmed desorption (TPD). The catalytic activity of the as-synthesized 3wt% Pr-Ni/α-Al2O3 catalyst was evaluated in a stainless steel fixed bed reactor at temperatures that ranged from 973K to 1073K and a weight-hourly-space-velocity (WHSV) of 4.5×104mlg−1h−1 under the atmospheric condition. The main gaseous products from catalytic glycerol pyrolysis were H2, CO, CO2 and CH4 (descending ranking) with the highest H2 formation rate and H2 yield of 0.02593molgcat−1s−1 and 29.04%, respectively. The analysis of the kinetic data obtained from the glycerol pyrolysis showed activation energy of 37.36kJmol−1. Based on the mechanistic modeling, it can be deduced that the rate determining step of the glycerol pyrolysis was via a single site associative adsorption with molecular surface reaction as the rate-determining step.

Enhancing the deN2O activity of the supported Co3O4|α-Al2O3 catalyst by glycerol-assisted shape engineering of the active phase at the nanoscale

A series of supported Co3O4/α-Al2O3 catalyst synthesized by glycerol-assisted method was thoroughly characterized (X-ray micro-tomography, XRD, RS, FTIR, SEM/TEM/EDX, TG/DTA, TPR), and their reactivity was evaluated in N2O decomposition in 5% N2O/He and 1.5% N2O, 1% NOx, 1 vol.% H2O, 2.0 vol.% O2. Their superior catalytic activity in comparison to the benchmark Co3O4/α-Al2O3 catalyst, obtained via incipient wetness impregnation with the aqueous solution, was accounted for by differences in cobalt spinel dispersion on the alumina support, spinel nanoparticle size and faceting. Whereas for the samples prepared from the aqueous solution the spinel active phase exhibits a broad bimodal size distribution (with the maxima for 10–50nm crystallites and 300–600nm agglomerates) in the case of glycerol-assisted synthesis a monomodal distribution is featured by isolated spinel nanocrystallites of 10–30nm. At the same time, the presence of glycerol changes the spinel crystallites morphology from rhombicuboctahedron with abundant exposition of the less favorable (111) planes into the truncated cubic shape with the dominant more active (100) facets. It was shown that the beneficial effect of glycerol is sustained in typical gaseous residuals (H2O, NOx, O2) present in the tail gases of nitric acid plants. The observed effect of glycerol-assisted synthesis was accounted for by complexation of cobalt by glycerol, leading to the formation of an intrapore cobalt glycerolate, which upon calcination is transformed into well dispersed Co3O4 cubic nanocrystals.