Al Catalyst Research Articles

Conversion of glycerol to lactic acid over Cu–Zn–Al and Cu–Cr catalysts in alkaline solution

Abstract A Cu–Zn–Al catalyst (from Johnson Matthey) and a Cu–Cr catalyst (form Strem Chemicals) were used for catalyzing glycerol dehydrogenation to produce lactic acid (LA) in alkaline aqueous solution. These catalysts were pre-reduced with hydrogen before use. Cu–Zn–Al exhibited much better performances than Cu–Cr, because the former had much larger surface area and higher copper content than the latter. The effects of reaction temperature (between 100 and 175 °C) reaction time, alkaline and catalyst concentrations on glycerol conversion and product yields were studied for the Cu–Zn–Al catalyst. LA selectivity was essentially constant (∼85%) until 95% conversion, and reached 96% at 98.9% conversion (LA yield was 94.9%) and 175 °C, which was much better than that reported previously with a CuO/Al2O3 catalyst. The rate of glycerol disappearance exhibited first-order dependence on glycerol concentration, and the rate constant increased linearly with catalyst concentration, suggesting that glycerol dehydrogenation on copper surface was the rate-limiting step. The yields of two major by-products (1, 2-propanediol and glyceric acid) decreased when glycerol conversion was high, ascribed to the reversibility of the by-products formations and the decrease of 1, 2-propanediol/LA generating rate ratio with increasing alkaline concentration.

Partial oxidation of methane on co-precipitated Ni–Mg/Al catalysts modified with copper or iron

Methane transformation to hydrogen and synthesis gas (CO + H2) by heterogenous catalysts can play an important role to secure the supply of energy, chemicals and fuels in the future. Methane is the main constituent of natural gas and biogas and it is also found in crystalline hydrates at the continental slopes of many oceans. In view of this vast reserves and resources, the use of methane as chemical feedstock has to be intensified. In this present work, (NiMg)Al catalysts doped with Fe or Cu, prepared by co-precipitation method and characterized by different techniques, were studied in the partial oxidation of methane (Treaction = 750 °C, CH4/O2 ratio = 2). The effect of catalyst composition and pre-treatment conditions of these catalysts were investigated. Also, these catalysts show a very high activity and selectivity in the partial oxidation reaction, which depends on the conditions of catalysts preparation. The obtained results indicated increasing of activity and selectivity with decreasing calcination temperature and increasing nickel and aluminium contents in the catalysts composition. The solid doped with iron constituted the best catalyst for the total oxidation of methane and for the water–gas shift reaction. On the other hand, the addition of copper was remarkably improved the catalytic performances of the (NiMg)Al solid. So, the presence of this element supported the partial oxidation of methane with production of syngas (CO + H2). With the addition of iron or copper for the catalyst composition, we were observed (in our previous work) the possibility of formation of NiM (M = Fe or Cu) alloy which increased nickel particles dispersion. In the case of copper, the reducibility of NiO was also assisted (TPR results) which increased catalytic activity in partial oxidation of methane.

Vapor Phase Hydrogenolysis of Furanics Utilizing Reduced Cobalt Mixed Metal Oxide Catalysts

AbstractVapor phase hydrogenolysis of both furfuryl alcohol and furfural are investigated over reduced Co based mixed metal oxides derived from the calcination of a layered double hydroxide precursor. Although a reduced cobalt‐aluminum oxide sample displays promising selectivity towards 2‐methylfuran (2‐MF) production, the addition of an Fe dopant into the oxide matrix significantly enhances the activity and selectivity per gram of catalyst. Approximately 82 % 2‐MF yield is achieved at high conversion if furfuryl alcohol is fed into the reactor at 180 °C over the reduced 3Co‐0.25Fe‐0.75Al catalyst. Based on structural characterization studies including temperature‐programmed reduction (TPR), X‐ray photoelectron spectroscopy (XPS), and in situ X‐ray absorption spectroscopy (XAS) it is suggested that Fe facilitates the reduction of Co, allowing for formation of more metallic species. Overall, this study demonstrates that non‐precious metal catalysts offer promise for the selective conversion of a key biomass oxygenate to a proposed fuel additive.

Natural gas reforming of carbon dioxide for syngas over Ni–Ce–Al catalysts

A series of Ni–Ce–Al composite oxides with various Ni molar contents were synthesized via the refluxed co-precipitation method and used for natural gas reforming of CO2 (NGRC) for syngas production. The effect of Ni molar content, reaction temperature, feed gas ratio and gas hourly space velocity (GHSV) on the Ni–Ce–Al catalytic performance was investigated. The Ni10CeAl catalyst was selected to undergo 30 h stability test and the conversion of CH4 and CO2 decreased by 2.8% and 2.6%, respectively. The characterization of the reduced and used Ni10CeAl catalyst was performed using BET, H2-TPR, in-situ XRD, TEM, and TGA-DTG techniques. The in-situ XRD results revealed that Ce2O3, CeO2 and CeAlO3 coexisted in the Ni10CeAl catalyst after reduction at 850 °C for 2 h. The results of the TEM analysis revealed that the Ni particle size increased after the NGRC reaction, which mainly caused the catalyst deactivation.

Hydrogen production with a low carbon monoxide content via methanol steam reforming over CuxCeyMgz/Al2O3 catalysts: Optimization and stability

Catalytic activities of Ce–Mg promoted Cu/Al2O3 catalysts via methanol steam reforming was investigated in terms of the methanol conversion level, carbon monoxide selectivity and hydrogen yield. The factors chosen were the reaction temperature, copper content, Mg/(Ce + Mg) weight-percentage and steam to carbon ratios. The catalysts were prepared by co-precipitation and characterized by means of XRD, BET, H2-TPR, and FESEM. The Ce–Mg bi-promoter catalysts gave higher performance due to magnesium penetration into the cerium structure causing oxygen vacancy defects on the ceria. A response-surface-model was then designed to optimize the condition at a 95% confidence interval for complete methanol conversion to a high H2 yield with a low CO content, and revealed an optimal copper level of 46–50 wt%, Mg/(Ce + Mg) of 16.2–18.0%, temperature of 245–250 °C and S/C ratio of 1.74–1.80. No deactivation of the Cu0.5Ce0.25Mg0.05/Al catalyst was observed during a 72-h stability test.

Recyclable bifunctional aluminum salen catalyst for CO2 fixation: the efficient formation of five-membered heterocyclic compounds

A variety of unique Al(salen) complexes functionalized by imidazolium-based ionic liquid (IL) moieties with the salen ligand at the two sides of 3,3′-position have been successfully prepared, rather than familiar 5,5′-position reported previously. The catalytic activity obtained by these bifunctional catalysts could be superior to those of the binary type catalysts in the formation of five-membered heterocyclic compounds from the cycloaddition reaction of CO2 and three-membered heterocyclic compounds (including terminal epoxides and N-substituted aziridines), presumably due to the distinguished intramolecularly synergistic catalysis, which might lead to perform the cycloaddition reaction at ambient conditions and retain excellent yield and unprecedented chemo- or regioselectivity. Moreover, the polyether-based trifunctional Al(salen) catalysts with the best catalytic performance could be regenerated and reused at least eight times without any obvious decreases in catalytic activity. Finally, the kinetic investigation suggested the structure of catalysts had important influences on the catalytic activity, thereby proposing the possible reaction mechanism.

Surface Modification of η–Al2O3 by SiO2 Impregnation to Enhance Methanol Dehydration Activity

Silica impregnated η‐Al2O3 catalysts (Si(number)Al) were prepared for methanol dehydration, with the number indicating the Si wt % added to η‐Al2O3. The Si(0.25)Al and Si(0.50)Al catalysts with the greatest number of acid sites had the highest methanol dehydration activities among the prepared catalysts. Si addition up to 0.5 wt % increased the number of the acid sites, which was slightly decreased by further Si addition. The number of weak acid sites correlated well with the catalytic activity for methanol dehydration, but was not enough to explain the higher activity of the catalysts containing silica compared with η‐Al2O3. The acid sites of the Si(1.0)Al catalyst were less than those of the η‐Al2O3 catalyst but the two had similar activity. Si addition primarily increased the Lewis acid sites, although it generated a few new Brønsted acid sites and chemical hydrogen bonded sites. Nonetheless, it was apparent that the increase of Lewis acid sites was the main reason for the enhancement of η‐Al2O3 activity by SiO2 addition. On the other hand, the new Brønsted and Lewis acid sites and the chemical hydrogen bonded sites created by Si addition should not be neglected.

Syngas production by the CO2 reforming of CH4 over Ni–Co–Mg–Al catalysts obtained from hydrotalcite precursors

The catalytic performance of the Ni, Co, Mg, and Al mixed-oxide solids, synthesized via hydrotalcite route, was investigated towards the dry reforming of methane for hydrogen production. The hydrotalcite structure was successfully obtained upon the synthesis. After calcination at 800 °C under an air flow, this structure was completely decomposed and the resulting oxides (CoxNiyMgzAl2800, x and y = 0; 1; 2; 3; 4, z = 2; 4, x + y + z = 6, x, y, and z are the molar ratios) were used as catalysts and were characterized using X-ray diffraction and Temperature-Programmed Reduction. The dry reforming of methane was carried out using a mixture of CH4:CO2 (1:1) after 2 h of reduction under an H2 flow at 800 °C. Co2Ni2Mg2Al2800 showed the highest catalytic activity in the studied series, ascribable to an interaction between Ni and Co, which is optimal for such Co/Ni ratio. The post-reaction characterization of the catalytic samples by X-ray diffraction and Differential Scanning Calorimetry evidenced a better resistance towards carbon deposition for the catalysts where Co molar ratio is higher than Ni.

Upgrading of glycerol from biodiesel synthesis with dimethyl carbonate on reusable Sr–Al mixed oxide catalysts

The high demand for renewable energy has led to the upsurge of methanol-assisted biodiesel synthesis. Therefore, glycerol as a byproduct entered the waste stream given the oversupply of biodiesel to the market. The dimethyl carbonate (DMC)-assisted transesterification of glycerol on a catalyst has been a popular approach for converting glycerol into valuable glycerol carbonate (GLC). The synthesis of GLC from the DMC-assisted transesterification of glycerol on mixed oxide catalysts (Srx–Al) with different Sr/Al ratios was examined in this study. A glycerol conversion of 99.4% and a GLC yield of 100% were achieved in a catalyst with Sr/Al=0.5 (Sr0.5–Al). Both values are higher than those in catalysts synthesized with Sr/Al=0.25 and 0.75. The Sr0.5–Al catalyst withstood five transesterification reaction cycles without a serious deactivation induced by the leaching of active SrO. Therefore, the Sr0.5–Al catalyst is suitable for consecutive uses in the DMC-assisted transesterification of glycerol with DMC into GLC.

Preparation of cerium doped Cu/MIL-53(Al) catalyst and its catalytic activity in CO oxidation reaction

Metal-organic framework (MOF) material MIL-53(Al) with high thermal stability was prepared by a solvothermal method, serving as a support material of cerium doped copper catalyst (Ce-Cu)/MIL-53(Al) material for CO oxidation with high catalytic activity. The catalytic performance between the (Cu-Ce)/MIL-53(Al) and the Cu/MIL-53(Al) catalytic material was compared to understand the catalytic behavior of the catalysts. The catalysts were characterized by thermogravimetric-differential scanning calorimetry (TG-DSC), N2 adsorption- desorption, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The characterization results showed that MIL-53(Al) had good stability and high surface areas, the (Ce-Cu) nanoparticles on the MIL-53(Al) support was uniform. Therefore, the heterogeneous catalytic composite materials (Ce-Cu)/MIL-53(Al) catalyst exhibited much higher activity than that of the Cu/MIL- 53(Al) catalyst in CO oxidation test, with 100% conversion at 80 °C. The results reveal that (Cu-Ce)/MIL- 53(Al) is the suitable candidate for achieving low temperature and higher activity CO oxidation catalyst of MOFs.

Transformation of bioethanol to 1,3-butadiene and other bulk chemicals over the surface of Mg–Al catalysts

The synthesis of bulk chemicals from bioethanol and analysis of the product distribution over Mg–Al catalysts were investigated.

Investigation into 1,3-butadiene and other bulk chemicals' formation from bioethanol over Mg–Al catalysts

Mg–Al catalysts were adopted in the direct synthesis of 1,3-butadiene and other bulk chemicals from bioethanol.

Ruthenium promoted cobalt–alumina catalysts for the synthesis of high-molecular-weight solid hydrocarbons from CO and hydrogen

The effect of the ruthenium promotion of Fischer–Tropsch (FT) cobalt–alumina catalysts on the temperature of catalyst activation reduction and catalytic properties in the FT process is studied. The addition of 0.2–1 wt % of ruthenium reduces the temperature of reduction activation from 500 to 330–350°C while preserving the catalytic activity and selectivity toward C5+ products in FT synthesis. FT ruthenium-promoted Co–Al catalysts are more selective toward higher hydrocarbons; the experimental value of parameter αASF of the distribution of paraffinic products for ruthenium-promoted catalysts is 0.93–0.94, allowing us to estimate the selectivity toward C20+ synthetic waxes to be 48 wt %, and the selectivity toward C35+ waxes to be 23 wt %. Ruthenium-promoted catalysts also exhibit high selectivity toward olefins.

Conversion of HMF to methyl cyclopentenolone using Pd/Nb2O5 and Ca–Al catalysts via a two-step procedure

An isolated yield of MCP of 58% was obtained from HMF on Pd/Nb2O5, which was prepared using cyclohexene as a reductant, and Ca–Al.

Highly Active Mixed-Phase Cu–Al Catalyst for Methanol Steam Reforming

Highly Active Mixed-Phase Cu–Al Catalyst for Methanol Steam Reforming

Oxidative cracking of vacuum residue with steam over NiK/CeZr–Al catalysts

NiK catalysts supported on CeyZr1−yO2–Al2O3 (NiK/xCeZr–Al) (x=0, 5, 10, 20, 30, and 40) systems were prepared as novel catalysts for cracking of vacuum residue with steam and their catalytic performances were tested using a fixed bed reactor at 500°C and under atmospheric pressure. The addition of Ce and Zr was found to greatly improve the catalytic performance, increasing the total yield of liquid plus gaseous products as well as the H/C ratio of the liquid products. Active oxygen species were generated from steam over zirconia particles and then spilled over the CeyZr1−yO2 surface, where oxidative cracking of heavy oil occurred to produce CO2 and lighter molecules. Active hydrogen species obtained from steam decomposition were then added to these lighter molecules on nickel active phases, resulting in the increased H/C ratio of the liquid products. Oxidative cracking with steam over NiK/CeZr-Al catalysts has great potential as industrial processes of vacuum residue cracking.

Zn–Ca–Al mixed oxide as efficient catalyst for synthesis of propylene carbonate from urea and 1,2-propylene glycol

A series of Zn–Ca–Al oxides with different CaO and ZnO contents have been prepared and evaluated in the synthesis of propylene carbonate (PC) from 1,2-propylene glycol (PG) and urea in a batch reactor. The effect of catalyst composition, basicity and reaction process parameters such as temperature, catalyst dose, molar ratio of PG to urea, purge gas flow and reaction time has been studied to find suitable reaction conditions for the PC synthesis. The PC selectivity and yield under the desired conditions could reach 98.4% and 90.8%, respectively. The best performing catalyst also exhibited a good reusability without appreciable loss in the PC selectivity and yield after five consecutive reaction runs. In addition, a stepwise reaction pathway involving a 2-hydroxypropyl carbamate intermediate was proposed for the urea alcoholysis to PC in the presence of Zn–Ca–Al catalysts, according to the time dependences of reaction intermediates and products.

Development of Fe-Promoted Ni–Al Catalysts for Hydrogen Production from Gasification of Wood Sawdust

The production of renewable hydrogen-enriched gas from biomass waste is a promising technology for the development of a sustainable economy and society. Until now, there are still challenges of the technology in terms of the efficiency of hydrogen production. A catalyst is known and has been tested to enhance hydrogen production from biomass gasification, in particular, using Ni-based catalysts, which have high reactivity for hydrogen production and are cost-effective. However, developing a Ni-based catalyst with high thermal stability and resistance of coke deposition on the surface of the catalyst is still a challenging topic. In this work, Ni–Al catalysts doped with low-cost Fe metal were investigated for hydrogen-enriched syngas production from gasification of biomass using a two-stage fixed bed reactor. NiO–Fe2O3–Al2O3 catalysts with various Ni/Fe molar ratios (9:1, 8:2, 6:4, 5:5, 4:6, 2:8, and 1:9) were studied, aiming to understand the influence of Fe addition on the production of hydrogen and the ...

Effect of the grain diameter of Ni-based catalysts on their catalytic properties in the thermocatalytic decomposition of methanol

The influence of grain size on the catalytic activity of Ni-based solid-state catalysts in the thermocatalytic decomposition of methanol was investigated. The carbon deposit, obtained during the catalytic activity and stability tests, was analyzed in detail by scanning electron microscopy (SEM), Brunauer–Emmett–Teller analysis (BET), and X-ray diffraction (XRD). It was found that the Ni 3 Al catalyst with a bigger grain diameter exhibits higher catalytic activity and stability in a methanol decomposition reaction. The reason for the differences in the catalytic activity and stability of solid-state catalysts depending on the grain diameter of the catalyst was proposed. At the tops of the obtained nanotubes/nanofibres, one can see Ni nanoparticles in all investigated Ni 3 Al thin foils with every tested grain size.

Mechanisms of the action of alkali metal admixtures on the properties of copper–zinc–aluminum water–gas shift catalysts

The effect of alkali metal (Cs, Na) admixtures on the catalytic and physicochemical properties of coprecipitated Cu–Zn–Al catalysts for the low-temperature water–gas shift reaction has been investigated. The inhibition of the formation of methanol, an undesired by-product, by alkali metals is accompanied by a decrease in the activity of the catalyst in the main, water–gas shift reaction ion. The alkali metals exert an adverse effect on the thermal stability of the catalyst. Experimental data are explained in a consistent way on the basis of the following conceptions of the mechanism of the action of alkali metals: (1) the alkali metals stimulate sintering of the crystal structure of the main components of the catalyst, diminishing the activity of the catalyst in the water–gas shift reaction and in methanol formation; (2) the alkali metals directly or indirectly accelerate methanol conversion into other chemical products.