Alumina-supported Catalysts Research Articles

Hydrothermal liquefaction of southern yellow pine with downstream processing for improved fuel grade chemicals production

The hydrothermal liquefaction (HTL) technique for liquefying lignocellulose biomass feedstock is often associated with low biocrude yield and poor fuel properties. This study examined the HTL of southern yellow pine sawdust and the hydrotreatment (HYD) of produced biocrudes in an effort to address these challenges. Pine HTL treatment was performed within water and water–ethanol mixed reaction medium at 250, 300, and 350℃ temperatures using metallic iron (Fe) as a catalyst. The rising reaction temperature in a water medium and increasing ethanol content in a mixed reaction medium were found to be effective in enhancing the biocrude yield from the non-catalytic pine HTL process. Maximum non-catalytic biocrude yield of 18 wt.% was produced in water at 350℃, whereas the ethanol and water (1:1 on mass basis) mixture generated the highest biocrude yield of 34 wt.% at 300℃ without any catalyst. The iron catalyst facilitated a maximum of 29 wt.% of biocrude yield as opposed to 18 wt.% without the catalyst at 350℃ in water. The use of an iron catalyst also raised the calorific value of produced biocrudes by 2.5–14 % within 250-350℃ in both water and water–ethanol media. The catalytic and non-catalytic biocrude products were chosen to undergo HYD treatment at 400 °C under high hydrogen pressure (initial 1000 psi) using an alumina-supported cobalt-molybdenum catalyst. The HYD treatment reduced the oxygen content of upgraded oils by 36–60 % compared to the parent HTL biocrudes with 35–37 MJ/kg calorific values. The simulated distillation detected the maximum gasoline range compounds in upgraded oil from catalyst and water–ethanol conditions, whereas the GC–MS analysis revealed the production of increased aromatic hydrocarbons in all upgraded HYD oils. This work has demonstrated the potential of ethanol and inexpensive iron catalyst in enhancing the biocrude production from pine, which could be upgraded to better fuel using the HYD process.

Advanced Electron Microscopy Characterisation of Aluminium-Oxygen Coordination in Catalyst Supports

Performance of alumina-supported catalyst systems are significantly affected by how the tetrahedral (Al-O4) and octahedral (Al-O6) coordination are mixed and blended with each other. Characterisation of aluminium-oxygen coordination is thus important to understand how catalysts interact with alumina at the microscopic level. Here we report the application of two advanced electron microscopy techniques on aluminium-oxygen coordination. The first technique is electron energy loss spectroscopy (EELS) that can reveal detailed electronic structure profile of aluminium valence band to analyse how aluminium is coordinated by oxygen. The second technique is pair distribution function (PDF) based on electron diffraction (ED), employed to measure aluminium-oxygen bond lengths associated with the coordination geometry.

Rational synergetic insight of Cs-Nb/Al2O3 toward promoted catalytic performance in aldol condensation of formaldehyde and methyl propionate

Acid-base properties and support effects are known to be instrumental in the formation of methyl methacrylate (MMA) upon the aldol condensation involving formaldehyde (FA) and methyl propionate (MP). In this work, four different alumina-supported Cs-Nb catalysts were fabricated and employed for the aldol condensation of FA and MP. It was noticed that Al2O3-B prepared by co-precipitation exhibited superior catalytic activity on account of its highest surface area and porosity as well as the highest content of Brønsted acid and five-coordinated Al. The comparison of integration manner revealed that closer proximity affords keener synergetic interaction, thereby multiplying catalytic performance. Furthermore, the association from acid-base characteristics to catalytic activity was established. Strikingly, the cutting-edge 10Cs-10Nb-Al2O3-B catalyst presented a single-pass lifetime of 150 h. The rational synergism in favor of lessening the energetic barriers for the processes of enolization and C–C bond formation was further verified by DFT calculations.

Enhanced coking resistance of alumina-supported cobalt nitride catalyst via doping of phosphorus for dry reforming of methane

A novel P-doped Co4N/γ-Al2O3 catalyst was firstly designed for dry reforming of methane (DRM). It was found that the use of P doping Co4N/γ-Al2O3 can enhance its coking resistance, which might be due to a decrease in CH4 dissociation ability and an increase in CO2 dissociation ability, as well as the increase of cobalt species capable of interacting with alumina.

Selective reduction of CO2 to CO over alumina-supported catalysts of group 5 transition metal carbides

We show the applicability of a preparation method, previously reported for obtaining tailored bulk VCx catalysts, for alumina-supported G5TMCs. The characteristics of the G5TMCs/Al2O3 catalysts and their behaviour in the selective reduction of CO2 to CO through the RWGS reaction is reported. VCx/Al2O3 catalysts were active, stable and highly selective; meanwhile NbC/Al2O3 and TaC/Al2O3 were not active. VCx/Al2O3 catalysts exhibited selectivity to CO over 99.5 % at temperature above 773 K. The characteristics of alumina-supported vanadium carbide particles depended on the vanadium precursor and on the atmosphere used during the catalyst preparation. XPS characterization of VCx/Al2O3 catalysts revealed the presence of carbide species on surface before and after RWGS reaction. The catalytic behaviour of VCx/Al2O3 is analysed in the light of their characteristics and compared with bulk VCx counterparts. The most performant catalyst, VC(Pr)/Al2O3, was stable over 4 days at 723 K, with ∼100 % selectivity to CO and CO2 conversion of ∼11 %.

Non-thermal plasma-catalytic ammonia synthesis over alumina-supported iron catalyst: Insights into the effect of alumina calcination temperature

Non-thermal plasma-catalytic ammonia synthesis (NTPCAS) has been regarded as a promising route to store hydrogen by utilizing renewable electricity. Alumina is a suitable support of the catalysts in NTPCAS and its properties can influence the performance of catalysts remarkably. In this study, the influence of the alumina calcination temperatures (Tc) on the catalytic performance of Fe-Al-x (x represents the value of Tc) was analyzed in a dielectric barrier discharge (DBD) reactor for NTPCAS. The results suggested that an increase in Tc transforms the alumina crystalline from γ phase to α phase. The best performance with a synthesized ammonia concentration of 11833 ppm was achieved over Fe-Al-900 with coexisting γ and θ phases of alumina under N2: H2 = 1:1 and SEI = 37.05 kJ/L conditions, which was 37 % higher than that of Fe-Al-800 with only γ phase. In addition, the larger Tc (i.e. 1100 and 1200 °C) decreased the specific surface area, increased the mean catalyst particle size, and led to the non-uniform dispersion of Fe species. The NH3-TPD and XPS studies suggested that an increase in Tc could influence the surface acidity and oxygen vacancy concentration of Fe catalysts, which were crucial to adjusting the catalytic activity for NTPCAS. This study clarifies the value of a suitable design of support of catalysts for improving NTPCAS.

Alumina-supported multi-metal catalyst for e-waste management for reclamation of valuable products

ABSTRACT Electronic and electrical waste (e-waste) has increased exponentially due to the humungous growth in the information technology and communication sector. Many multi-metal catalysts are developed by researchers for electronic waste plastic conversion into fuel products and recovery of valuable metals. In the present study, an Alumina-supported catalyst powder with selected transition metals metal oxides was prepared to improve the yield of hydrocarbon liquids. FESEM with energy-dispersive spectroscopy, XRD and laser diffraction particle size analysis were used to characterise catalysts. The shredded e-waste chips to catalyst weight ratio was maintained from 2:1 to 10:1 and studied. The experiments were conducted with a reaction temperature range from 300°C to 500°C. The produced fuel density was 0.88 kg/L, with 0.75 liquid fuel conversion and 71.7% overall liquid fuel yield. The light gas percentage was 4–6%. NMR analysis, bomb calorimetric study and gas chromatography-mass spectroscopy of liquid fuel analysis suggest carbon chain compounds of C3–C20 hydrocarbon, indicating a mixture of petrol and diesel-like liquid products. The catalyst can be tuned to improve liquid fuel conversion. The liquid fuel product is promising for fuel use, however, upgrading treatments are needed to meet standard product specifications.

Effect of the amount and type of active metal and its impregnation sequence on bio-fuel production

This study aims to investigate biofuel production from biomass-derived bio-oil and examine the impact of selecting different active metals, their quantities, and synthesis procedures on biofuel selectivity. For this purpose, alumina-supported catalysts containing Zr, Co, and W were prepared using the wet impregnation method. Some physical and chemical properties of the synthesized catalysts were determined through XRD, BET, SEM/EDS, ICP-MS, TGA-DTA, and DRIFTS analysis. The activity test studies revealed that the 5Co-10Zr@MA catalyst, prepared by co-impregnation, exhibited the highest bio-oil conversion (95 %) and the highest iso-paraffin selectivity (93 %). XRD analysis indicated that this catalyst possess the CoAl2O4 structure, indicating the formation of an alloy between alumina and cobalt, thereby enhancing catalytic activity. The reusability tests showed that the 5Co-10Zr@MA catalyst maintained its activity over a time of 3 h. Consequently, the utilization of mesoporous alumina-supported bimetallic catalysts has proven to be successful in the production of biofuels, achieving high conversion and selectivity.

Porous Alumina-Supported Tungstated Zirconia Catalysts for Heptane Isomerization

Porous Alumina-Supported Tungstated Zirconia Catalysts for Heptane Isomerization

Carbon dioxide conversion to fuel over alumina-supported ruthenium catalysts

In this study, ruthenium-based catalysts were prepared for CO2 hydrogenation. Incipient-wetness-impregnation of the alumina-support with ruthenium (III) nitrosyl nitrate solution to achieve 0.5 wt% Ru loading on supports was used to prepare these catalysts. Potassium (0–3 % wt%) was used to further promote the catalysts. TPR, CO2-TPD, XRD, TEM, XPS, SEM, and EDS analyses were used to characterize catalyst properties. The hydrogenation of CO2 catalytic tests were conducted and the effect of operating conditions (temperature, pressure, and space velocity) were investigated. These studies were conducted in a tubular fixed-bed reactor. The CO2 conversion over these catalysts was found to be low and the dominating product observed was CH4 with a small amount of C2+ forming when K was added to the catalyst. The optimum potassium loading for improved C2+ product yield over Ru/Al2O3 was 1%K for CO2 hydrogenation.

Hydroconversion of lignin-derived platform compound guaiacol to fuel additives and value-added chemicals over alumina-supported Ni catalysts

Hydroconversion of guaiacol (GUA) over γ-Al2O3 and phosphatized-γ-Al2O3 (γ-Al2O3(P)) supported Ni catalysts was initiated by Lewis-sites and active Ni sites. Conversion proceeded via transmethylation and hydrodemethylation/hydrodemethoxylation as major and minor pathways, respectively, resulting in mainly catechol and methylcatechols, and via series of consecutive hydrodehydroxylation (HDHY) and ring hydrogenation (HYD) reactions leading to partially and fully deoxygenated, saturated, and unsaturated products. High Ni-loading and high H2 pressure promoted the formation of cyclohexane and methyl-substituted cyclohexanes; however, above 300 °C the hydrogenation–dehydrogenation equilibrium favored the formation of benzene and methyl-substituted benzenes. Ni/γ-Al2O3(P) showed suppressed HYD/HDHY activity resulting in pronounced formation of catechol and/or phenol and their methyl-substituted derivatives. Surface phenolate species were substantiated as surface intermediates of hydrodeoxygenation. Phosphatizing reduced the concentration of both basic OH and Lewis acid (Al+) – Lewis base (O–) pair surface sites of the γ-Al2O3 support and, thereby, suppressed phenolate formation and hydrodeoxgenation.

Effect of Iron Content in Alumina-Supported Palladium Catalysts and Their Reduction Conditions on Diclofenac Hydrodechlorination in an Aqueous Medium

Effect of Iron Content in Alumina-Supported Palladium Catalysts and Their Reduction Conditions on Diclofenac Hydrodechlorination in an Aqueous Medium

A site distance dependence of product selectivity in n-hexane dehydrogenation over alumina-supported chromium catalyst

Although CrOx/Al2O3 has been widely applied for light alkanes dehydrogenation, there is insufficient understanding on the dehydrogenation of long-chain alkanes that no solutions to the poor selectivity to mono-olefins and high yield of aromatics. Herein, dehydrogenation of n-hexane was studied on a series of CrOx/γ-Al2O3 catalysts with different densities of Cr sites, and it finds that the dehydrogenation performance is closely related to the distance between Cr sites. With densely populated Cr sites, multiple H atoms of n-hexane are adsorbed on the CrOx/γ-Al2O3 simultaneously (i.e., multi-point adsorption), promoting the formation of n-hexadiene, n-hexatriene and the resultant benzene and/or coke. Therefore, when the Cr loading exceeds the mono-layer coverage (5 wt% Cr loadings), the selectivities to n-hexenes and benzene are kept constant (about 23 wt% and 68 wt%, respectively). While decrease of Cr content in the mono-layer regime leads to a significant decrease in both the distance between Cr sites and the number of adsorbed H atoms, resulting in improved selectivity to n-hexenes. The CrOx@γ-Al2O3 catalyst with 3.6 Cr atoms/nm2 prepared by the equilibrium adsorption method (and the complexation of CrIII and 3,5-dimethylpyridine), exhibits 89 wt% selectivity to n-hexenes (<2 wt% for benzene). This work provides theoretical guidance for the precise design and synthesis of the high-performance CrOx-based catalyst for the dehydrogenation of alkanes, especially for long-chain alkanes.

Synergistic structural and electronic influences of Pt bead catalysts on dehydrogenation activity for liquid organic hydrogen carriers

Alumina-supported Pt bead catalysts with uniform (PtU/θ-Al2O3) or egg-shell (PtE/θ-Al2O3) structure and their corresponding potassium-doped counterparts (K-PtU/θ-Al2O3, K-PtE/θ-Al2O3) were synthesized to elucidate the influence of structure-induced active metal distribution and promotor on the dehydrogenation of liquid organic hydrogen carriers (LOHCs). Characterizations of the catalysts confirmed that different synthetic methods led to distinct Pt distributions on the Al2O3 surface. PtE/θ-Al2O3 and K-PtE/θ-Al2O3 had an average size of 1 nm with narrow Pt distributions while PtU/θ-Al2O3 and K-PtU/θ-Al2O3 exhibited bimodal distributions in Pt particle size (<0.2 nm and <0.8 nm), which also influenced the oxidation states. Introducing the promotor (K) facilitated electron transfer into Pt, which resulted in a more metallic state. When applied to the dehydrogenation of two different LOHCs, including methylcyclohexane and perhydro-monobenzyltoluene, K-PtE/θ-Al2O3 exhibited superior catalytic activity and durability compared to other catalysts. The improved activity of K-PtE/θ-Al2O3 was primarily attributed to the combined electronic influences of the catalyst bulk structure and promotor.

Gas phase oxidative dehydrogenation of cyclohexane over Alumina-Supported Copper-Manganese oxide Catalyst: in-situ DRIFTS studies

Oxidative dehydrogenation (ODH) is a promising technique for converting Cyclohexane (Cy-H) to Cyclohexene (Cy-ene). However, this reaction yields undesired byproducts (Benzene and CO2) due to deep-dehydrogenation and over-oxidation. Therefore, controlling reaction parameters, comprehending intermediate species, and optimizing catalyst design are crucial for enhancing selective Cy-ene formation. Copper-manganese oxide catalysts were synthesized via the incipient wetness impregnation technique. A solid solution (CuMnOδ) exhibited superior catalytic activity due to synergistic interaction and active site formation. The study elucidated that copper oxide facilitates the deep-dehydrogenation of Cy-H. While manganese oxide incorporation inhibits CO2 and benzene formation, promoting partial dehydrogenation to Cy-ene. The studies unveiled Cy-H activation via hydrogen abstraction, forming Cyclohexanolate intermediates interacting with surface hydroxyls, yielding Cy-ene via dehydration. Notably, Cy-one formation via Enolate intermediates was also observed. The catalyst 10Cu0.25Mn0.75Oδ/Al2O3 exhibited the highest Cy-ene yield (∼12.1 %), facilitated by the synergistic effect, with a Cy-H conversion (∼15.7 %) at 300 °C.

Cyanide removal from aqueous solution by oxidation with hydrogen peroxide in the presence of activated alumina-supported copper catalyst

&lt;p&gt;Cyanide compounds are widely used in some electroplating, chemical and metallurgical industries. They are often found in their liquid discharges. This work highlights the performance of an activated alumina-supported copper catalyst in the removal of cyanide by oxidation with hydrogen peroxide in aqueous solution. The influence of catalyst dose, initial molar ratio of hydrogen peroxide/cyanides, temperature, and catalyst reuse was studied. The activated alumina-supported copper significantly enhanced the reaction rate showing a good catalytic activity. The efficiency of cyanide elimination was increased after 30 minutes of oxidation from 48% to 98% by increasing the catalyst dose from 1 to 10 g/L. Rising the temperature from 30°C to 40°C promoted cyanide removal. The catalyst can be recycled four times and show good stability. The kinetics of cyanide oxidation was revealed to be pseudo-first order with regarding cyanides. The rate constants as well as the activation energy were determined.&lt;/p&gt;&#x0D;

Effect of Residence Time and Carrier Gas on the Dehydrogenation of n-Hexane over Alumina-supported Chromium Catalyst

CrOx/γ-Al2O3 catalyst was prepared by incipient wetness impregnation method, and the influence of residence time and carrier gas on the dehydrogenation of n-hexane were studied. It is found that n-hexane dehydrogenation over CrOx/γ-Al2O3 catalyst with H2 as carrier gas exhibits totally different catalytic behaviors with that of diluting n-hexane with N2. When diluting feed with N2, the selectivity to dehydrogenation product is promoted while the cracking reaction is exhibited with reducing residence time. However, the selectivity to dehydrogenation product is significantly decreased while the isomerization of n-hexane is promoted when using H2 as carrier gas. It is proposed that H2 undergoes dissociation on the dehydrogenation active site, and further facilitates the olefinic dehydrogenation products to form carbocation, which performing isomerization reaction on the acid site on the γ-Al2O3 surface. Therefore, the isomerization of n-hexane is promoted in cost of the selectivity to dehydrogenation product when using H2 as carrier gas.

Advances in morphology-controlled alumina and its supported Pd catalysts: synthesis and applications.

Alumina materials, as one of the cornerstones of the modern chemical industry, possess physical and chemical properties that include excellent mechanical strength and structure stability, which also make them highly suitable as catalyst supports. Alumina-supported Pd-based catalysts with the advantages of exceptional catalytic performance, flexible regulated surface metal/acid sites, and good regeneration ability have been widely used in many traditional chemical industry fields and have also shown great application prospects in emerging fields. This review aims to provide an overview of the recent advances in alumina and its supported Pd-based catalysts. Specifically, the synthesis strategies, morphology transformation mechanisms, and structural properties of alumina with various morphologies are comprehensively summarized and discussed in-depth. Then, the preparation approaches of Pd/Al2O3 catalysts (impregnation, precipitation, and other emerging methods), as well as the metal-support interactions (MSIs), are revisited. Moreover, Some promising applications have been chosen as representative reactions in fine chemicals, environmental purification, and sustainable development fields to highlight the universal functionality of the alumina-supported Pd-based catalysts. The role of the Pd species, alumina support, promoters, and metal-support interactions in the enhancement of catalytic performance are also discussed. Finally, some challenges and upcoming opportunities in the academic and industrial application of the alumina and its supported Pd-based are presented and put forward.

Dry synthesis of alumina-supported cobalt catalyst for highly enhanced catalytic oxidation

Alumina-supported cobalt oxide excels as an oxidation catalyst, however, strong metal-support interactions (SMSI) of cobalt and alumina can lead to inactive phases such as cobalt aluminate. To avoid the formation of the inactive phase, it was hypothesized that reducing the number of hydroxyl group anchoring sites on the alumina would enable a higher ratio of active cobalt oxide than inactive phases. We devised a dry synthesis method combined with alumina dehydroxylation and solid-state impregnation of cobalt. Characterization results including XRD, XPS, and Raman spectroscopy confirm the formation of the desired active phase on the dehydroxylated alumina. The resultant catalysts demonstrate a surprising decrease in the cobalt content (max. tenfold from 20 wt.% to 2 wt.% of cobalt loading) for oxidations of NH3 and CO, respectively, suggesting practically useful synthesis method for highly active supported catalysts.

Structure evolution of porous alumina during aging process and its support effect on PtSn/Al2O3 catalyzed propane dehydrogenation

Precise control of porous alumina microstructures is always challenging due to the diversity and complexity of the growth process-related alumina crystalline phase and surface properties. In this work, we established a bottom-up synthesis route with a combination of rapid precipitation at high supersaturation and high-temperature aging in terms of enhancing particle aggregation kinetics. Surprisingly, we discovered that there were two distinct growth stages of alumina precursor (ammonium aluminum carbonate hydroxide) during the aging procedure, that is, oriented attachment at the early stage of crystallization and subsequent Oswald ripening. High-temperature aging can effectively strengthen the aggregation kinetics between the particles and produce large mesoporous (∼16 nm) and a remarkable number of defect sites with the exposure of up to 14 % unsaturated pentacoordinate aluminum ions. Owing to the presence of strong metal-support interactions, the alumina-supported PtSn catalyst exhibited excellent catalytic activity in the propane dehydrogenation reaction with propylene formation with 99 % selectivity and superior stability with a low deactivation rate of 0.007 h−1 over 24 h. These results suggested that it was feasible and instructive to achieve precise control of the structure and surface properties of alumina by manipulating the aggregation process of the initial particles during the aging stage.