Active Metal Content Research Articles

Fabrication of Gold and Silver Nanoparticles Supported on Zinc Imidazolate Metal-Organic Frameworks as Active Catalysts for Hydrogen Release from Ammonia Borane.

Well-dispersed Au and Ag nanoparticles (NPs) have been immobilized on a zinc imidazolate metal-organic framework, Zn(mim), using the "one-pot" method and tested as catalysts in ammonia borane hydrolysis. The AuNPs@Zn(mim) and AgNPs@Zn(mim) materials were characterized by FTIR, XRD, ICP-OES, TGA, BET, SEM, and TEM. The AgNPs@Zn(mim) catalyst showed a high yield (98.5%) and high hydrogen generation rate (3352.71 mL min-1 gAg -1) in NH3BH3 dehydrogenation. The determined activation energies (19.6 kJ mol-1 for AuNPs@Zn(mim) and 38.13 kJ mol-1 for AgNPs@Zn(mim)) are lower than those for most reported catalysts containing Au/Ag-MOF used in the hydrolysis of NH3BH3. Moreover, the catalysts tested here revealed good stability and reusability, preserving 71.42% (AuNPs@Zn(mim)) and 88.23% (AgNPs@Zn(mim)) of their initial catalytic activities after five consecutive cycles. In the case of AgNPs@Zn(mim), the combination of the simple and green synthesis method, low active metal content, relatively low cost, and moderate dehydrogenation conditions makes the material an excellent candidate to produce hydrogen from ammonia borane.

Thermal and cyclic performance of aluminum alloy composite phase change microcapsules for high-temperature thermal energy storage

Al alloys are suitable for high-temperature applications such as solar thermal power generation and industrial heat utilization. However, addressing the challenges of high-temperature corrosion and material failure in Al alloys is of paramount importance. In practical industrial applications, there is a need to develop encapsulation techniques applicable to a wider range of Al alloy types and phase change temperature ranges, exploring the universality of the technology and the diversity of application scenarios. In this study, a dual encapsulation was conducted on binary and ternary Al alloys (including Al-Ni, Al-Mg, Al-Si-Mg, and Al-Mg-Zn). Aiming at thermal energy storage, four composite phase change microcapsules (CPCM) were successfully prepared and subjected to material characterization, thermal performance analysis, and thermal cyclic tests in air environments. After 2000 thermal cycles, no cracks were observed on the surface of the four CPCMs, and the microstructure remained intact. The components of the CPCMs maintained good chemical compatibility. Among the four types of CPCMs, the Al-Si-Mg CPCMs exhibited the best thermal cyclic stability, with a latent heat reduction rate of 19.5 % after 2000 cycles. The experimental results indicated that the dual encapsulation strategy was effective for various types of Al alloy PCMs, thereby expanding the application of Al alloys in high-temperature thermal storage. Furthermore, Al alloys with more regular morphology and lower active metal content exhibited better thermal performance and cyclic capability, making them more suitable candidates for high-temperature thermal storage applications.

Intensified reforming reactor for blue hydrogen and nitrogen production

The development of Chemical-looping Reforming (CLR) for blue hydrogen production requires a precise reactor design and control to achieve optimal efficiency and operability. This study proposes a 1D heterogeneous model for a CLR fixed-bed reactor, targeting the production of blue hydrogen and nitrogen. Validation against experimental data confirms the model’s accuracy and reliability. A comprehensive sensitivity analysis highlights reactor variables, including active metal content in the oxygen carrier, steam-to-methane ratio, and molar flow rates during reduction and reforming stages, as key variables in determining reactor performance. Optimizing these variables is crucial for process intensification and enhancing hydrogen production efficiency. Under optimal conditions, the reactor yields nitrogen with a concentration above 98% during the oxidation stage and hydrogen with a 66.7% concentration during the reforming stage. Moreover, the CLR reactor operates autothermally and reaches a hydrogen production efficiency of 63.6%, prior to any further purification. The study concludes with a discussion of the reactor’s challenges and opportunities, laying the groundwork for potential future research and advancements in the field.

Enhanced low-temperature H2-selective catalytic reduction performance and selectivity of Pt/ZSM-5–TiO2 washcoated monolithic catalysts for NOx reduction

Hydrogen-selective catalytic reduction (H2-SCR) is a promising technology for reducing nitrogen oxide (NOx) emissions at low temperatures, but the selectivity of this process is limited by the generation of N2O. To achieve enhanced denitrification (deNOx) performance, H2-SCR catalysts with mixed zeolite and TiO2 supports washcoated on monolithic cordierite were developed. The catalyst support, active metal type and content, and monolithic cordierite cell density significantly influenced the H2-SCR performance. The xPt/TiO2 catalysts (where x is the metal content, wt.%) achieved >90% NOx conversion 135–180 °C, whereas the xPd/TiO2 catalysts exhibited poor H2-SCR activity, with <30% NOx conversion. In contrast to 0.5Pt/TiO2, the 0.5Pt/zeolite catalysts achieved high NOx conversion at 140–150 °C (91% at 140 °C for 0.5Pt/ZSM-5 > 89% at 140 °C for 0.5Pt/BETA >85% at 150 °C for 0.5Pt/SSZ-13), suggesting that zeolite supports significantly promote H2-SCR activity at low reaction temperatures. For the 0.5Pt/ZSM-5 washcoated monolithic catalyst, increasing the cell density from 400 to 900 cpsi significantly improved the NOx conversion from 52% to 90% at 100 °C owing to the increased geometric surface area and open frontal area of monolithic cordierite. For catalyst with mixed supports (0.5Pt/yZSM-5zTiO2) changing the ZSM-5/TiO2 ratio (y:z) from 25:75 to 90:10 increased the low-temperature NOx conversion from 39% to 89% at 100 °C, indicating that the deNOx characteristics can be tuned. With NO as the reactant, the 0.5Pt/90Z10T catalyst produced the lowest N2O share (8–17%) within the temperature window of maximum NOx conversion, resulting in an increased N2 share (83–88%). Thus, the synergetic effect of mixed ZSM-5/TiO2 catalyst supports can enhance low-temperature NOx conversion and mitigate N2O formation.

Room-Temperature Synthesis of Biogenic δ-MnO2 NPs for the Dehydrogenative Coupling of Diamines with Alcohols for Benzimidazole and Quinoxaline Synthesis: An Efficient Catalyst for Electrochemical Applications.

An efficient, unique, and eco-friendly biogenic synthesis of single-crystalline δ-phase manganese oxide nanoparticles (MnO2 NPs) using Gliricidia sepium leaves (GSL) extract at room temperature has been revealed for the first time. The active chemicals present in the GSL extract were found to serve as both reducing and stabilizing agents. The catalyst shows an excellent surface area of 301.13 m2 g-1, a mean pore diameter of 4.01 nm, and 39.97% w/w of active metal content. The reactivity of the synthesized catalyst was demonstrated by achieving a one-pot synthesis of benzimidazoles and quinoxalines via an acceptorless dehydrogenative coupling strategy utilizing biorenewable alcohols. The release of hydrogen gas was observed as the only side product and proven by its successful utilization for alkene reduction which supports the mechanistic elucidation. The release of hydrogen gas as a useful byproduct highlights the scientific importance of the present methodology. Additionally, gram-scale synthesis and catalyst recyclability studies are deliberated. Importantly, the δ-MnO2 NP catalyst exhibited superior catalytic activity and high durability toward hydrogen evolution reaction in alkaline media, highlighting the dual use of the catalyst. The δ-MnO2 NPs attain the current density of 10 mA/cm2 at an overpotential of 154 mV with a Tafel slope of 119 mV/dec.

Bimetallic cobalt catalysts promoted by La2O3 for the production of high-calorie synthetic gas

A new catalytic route for the production of a high-calorie synthetic gas (40–60 MJ/Nm3), composed by C1-C4 hydrocarbons, has industrial interest for gas applications and locations with high heating requirements. In this work, a series of bimetallic Co-X (X = Ni, Pt and Fe) catalysts supported on La2O3 promoted Al2O3 micro-spheres were evaluated using both CO2 and CO carbon sources under mild temperature (T = 200–300 °C), moderate pressure (P = 10 bar·g) and relatively high gas hourly space velocity (40,000 N mL/gcat·h). Experimental results proved that the incorporation of nickel as a second metal is beneficial for high-calorie gas application. Besides, catalytic results showed that the utilization of CO as carbon source is beneficial in both conversion and C1-C4 hydrocarbon selectivities. Co-Ni presented the most interesting results, leading to a heating value of 57.9 MJ/Nm3 (40.01 % CH4 and 50.04 % C2-C4 hydrocarbon) at 250 °C through CO hydrogenation. The enhanced catalytic performance achieved over bimetallic Co-Ni was attributed to CoNi alloy catalytic activity, high reducibility (73.82 %), active metal content (9.65x10-4 mmol/g) and appropriate acid-basic sites for COx activation. In contrast, the conversion of CO2 to high-calorie gas was found to be more challenging and lower gas heating values were achieved (39.73 MJ/Nm3). In this case, an adapted reactor concept using a dual bimetallic catalyst and different reaction conditions is hereby proposed to shift selectivity towards the targeted products. This findings represent a step forwards in catalytic engineering for the development of high-calorie synthetic gas reactors.

NiS gradient distribution on arrayed porous carbonized grapefruit peel for water splitting.

Metal-based catalysts on biomass carbon substrates can combine their respective advantages of composition and structure to improve the catalytic performance. Herein, NiS supported on grapefruit peel derived array porous carbon (APC) was obtained via a carbonization process without emission of toxic gases. The natural S source from grapefruit peel reacted with nickel salt solution. The gradient distribution of NiS and S on the APC substrates can be altered by the concentration of impregnating salt solution. Theoretical calculations showed that the S gradient distribution on APC could tune the electronic structure and optimize the adsorption energies of the intermediates. NiS was firmly anchored on the porous carbon framework, resulting in enhanced high intrinsic activity, exposure of more active sites, and accelerated mass transfer. The active mass density was proposed to build a relationship between active metal content and electrolyte diffusion capacity for the evaluation of catalytic properties.

Study on Ni/ZrO2 catalyst preparation

In this work, the influence of catalyst preparation temperature on its structure was investigated. We have synthesized 12 different Ni/ZrO2 catalysts by varying the calcination temperature, time, and active metal content, and these catalysts will be further used in the carbon dioxide methanation reaction. Structure and properties of the catalysts were determined using XRD and SEM analysis. Therefore, Ni content of the catalysts were measured by ICP-OES.Regarding to the crystal size calculation using XRD data by Scherer equation, when calcination time was increased the average crystal size of nickel oxide was decreased from 42.38 nm to 38.93 nm whereas it decreased to 39.23 nm when the calcination temperature was increased. This shows that the distribution of active metals in the catalyst increases when the heat treatment parameters are increased. In addition, it can be assumed that the activity of the catalyst can be enhanced when the calcination temperature and time were increases.

Catalysts Derived from Nickel-Containing Layered Double Hydroxides for Aqueous-Phase Furfural Hydrogenation

Changes in the structural and textural properties of NiAl-layered double hydroxides (LDHs) (with 2–4 molar ratios of metals) and state of nickel that occur in different steps of the synthesis of nickel catalysts were studied using XRD, thermal analysis, TPR, low-temperature nitrogen adsorption, XANES, EXAFS, and electron microscopy methods. Relations between nickel content, catalyst reduction conditions, state of nickel, and its catalytic properties were revealed. It was shown that the use of NiAl LDH as the catalyst precursor even at a high content of active metal allows for the obtaining of the dispersed particles of supported nickel that are active in the aqueous-phase hydrogenation of furfural. The catalyst activity and conversion of furfural were found to increase with elevation of the catalyst reduction temperature and the corresponding growth of the fraction of reduced nickel. However, a lower reduction temperature (500 °C) makes it possible to form smaller nickel particles with the size of 4–6 nm, and a high Ni content (Ni:Al = 4) can be used to obtain the active Ni@NiAlOx catalyst. Under mild reaction conditions (90 °C, 2.0 MPa), the furfural conversion reached 93%, and furfuryl alcohol was formed with the selectivity of 70%. Under more severe reaction conditions (150 °C, 3.0 MPa), complete conversion of furfural was achieved, and cyclopentanol and tetrahydrofurfuryl alcohol were the main hydrogenation products.

Effective catalytic steam reforming of naphthalene over Ni-modified ZSM-5 via one-pot hydrothermal synthesis

Ni-modified ZSM-5 catalysts are prepared by a one-pot hydrothermal synthesis method and applied to the steam reforming of naphthalene as a tar model compound. The effects of the reaction temperature, silica-alumina ratio (Si/Al) and metal content on the catalytic performance for reforming naphthalene are investigated. Characterization results indicate that the Ni-modified ZSM-5 catalysts maintain the original MFI structure of ZSM-5 and a portion of Ni is successfully introduced into the zeolite structure. When the reaction temperature is 800 °C, the conversion efficiency of naphthalene achieves 91.5% with a high yield (6.75%) of hydrogen. Zeolite catalysts with higher Si/Al ratios improve the conversion of naphthalene to syngas, demonstrating their better catalytic activity. An appropriate active metal content (2.4 wt%) contributes to the catalytic performance of the catalyst owing to the strong metal-support interaction, resulting in resistance to sintering and carbon deposition. The reaction mechanism involved in the catalytic reforming of naphthalene is proposed. The application of a novel one-pot hydrothermal synthesis method greatly promoted the catalytic activity of Ni@ZSM-5, which provided an appropriate and universal approach for the improvement and optimization of tar reforming catalysts.

Production of Hydrogen and Carbon Nanofibers by the Catalytic Decomposition of Methane over Ni-Containing Catalysts

This paper is devoted to technology for producing pure hydrogen by catalytic decomposition of light hydrocarbons. A set of nickel-containing catalysts was prepared using the corresponding salts. The content of active metal (Ni) varied from 10 to 90 wt %. The activity of the catalyst in the process of methane decomposition was studied. It has been found that the most promising method for the synthesis of catalysts is the melting of salts of metal. The maximum yield of hydrogen was 416 L/gcat at a Ni content of 90 wt % at a temperature of 675 °C and a pressure of 5 atm.

Maximizing paraffin to olefin ratio employing simulated nitrogen-rich syngas via Fischer-Tropsch process over Co3O4/SiO2 catalysts

The optimization of cobalt oxide (Co3O4) loading on silica for the low-temperature Fischer-Tropsch (LTFT) synthesis process employing simulated nitrogen-rich syngas (50 vol%) to produce highly paraffinic biodiesel is studied. Four different amounts of Co3O4 varying from 15 to 36 wt% were loaded on silica in order to examine the catalytic performance of Co/SiO2 catalysts. The supported catalysts were characterized using XRF, nitrogen physisorption, XRD, TPR, DRIFT and SEM fixed with EDS analysis. The performances of the catalysts were examined in a single channel fixed bed reactor employing simulated nitrogen-rich syngas (CO:H2:N2 = 17:33:50 vol%). The reactor was operated at P = 20 bar, T = 237 °C and WHSV = 3.0 Nl/h.gcat. The active site concentration was maximized by (i) utilizing all the available surface area of the sphere's porous support, (ii) using ethanolic impregnation solution to hinder sintering of Co3O4 phases due to presence of ethoxyl groups, and (iii) connecting oxide crystallites to the neighbouring pores by increasing the active metal content. As a result, the production of heavy hydrocarbons per unit of time was maximized with 36 wt% cobalt loading on silica (CO conversion and C5+ selectivity were 87.65 and 81.78 mol%, respectively, and also paraffin: olefin ratio was 98:2).

Oxidation Kinetics of 1,2-Propanediol in the Presence of Pd and Pt Catalysts

1.25 – 5wt%Pt/Al2O3, 1.25 – 5wt%Pd/Al2O3, 1wt%Pd/TiO2, 1 – 5wt%Pd/TiO2-NF, 1.25wt%Pt+1.25wt%Pd/Al2O3, 5wt%Pt/SiO2, 5wt%Pt/C catalysts were synthesised and tested in the selective oxidation of 1,2-propanediol by molecular oxygen. It was found that all catalysts were active in alkaline water solutions; lactic acid was obtained as the main product of the reaction. The conversion of 1,2-propandiol and the yield of lactic acid depended on the content of active metal in the catalysts. The most active for the oxidation of 1,2-propandiol were palladium-containing catalysts supported on TiO2 nanofibers (Pd/TiO2-NF). The highest 1,2-propanediol conversion (100 %) and lactic acid yield (96 %) were obtained using the 5wt%Pd/TiO2-NF catalyst at the following oxidation parameters: c0(1,2-propanediol) = 0.3 mol/L, P(O2) = 1 atm, n (1,2-propanediol)/n (Pd) = 500 mol/mol, t = 60 °C, c0(NaOH) = 1.5 mol/L.

Ni/La2O3 and Ni/MgO–La2O3 catalysts for the decomposition of NH3 into hydrogen

The decomposition of NH3 for hydrogen production was studied using Ni/La2O3 catalysts at varying compositions and temperatures prepared via surfactant-templated synthesis to elucidate the influence of catalyst active metal content, support composition and calcination temperature on the catalytic activity. The catalytic performance of all samples was studied between 300 and 600 °C under atmospheric pressure. The catalytic activity of the sample were as follows: 10Ni/La2O3-450 > 10Ni/La2O3-550 > 10Ni/La2O3-650 ≈ 10Ni/La2O3-750 ≈ 10Ni/La2O3-850. The excellent activity (100%) of 10Ni/La2O3-450 could be due to the high surface area, basicity strength and concentration of surface oxygen species of the catalyst as evidenced by BET, CO2-TPD and XPS. In addition, to adjust the activity of the catalyst support, the molar ratios of Mg and La were varied (1:1, 3:1, 5:1, 7:1 and 9:1). The 5Ni/5MgLa (5:1 M ratio) was found to be the most active (100%) relative to other Ni/MgLa formulations. Furthermore, the Ni content in the Ni/5MgLa sample was adjusted between 10 and 40 wt%. Increasing the Ni content of the catalysts increased NH3 conversion with the 40 wt% Ni formulation demonstrating complete NH3 conversion at 600 °C and a high gas hourly space velocities (GHSV) (30,000 mL∙h−1∙gcat−1).

Elucidating the role of the axial cysteine residue in NHase catalysis and the enzyme maturation

Nitrile hydratases are metalloenzymes that contain trivalent Fe/or Co ions in their active site, coordinated in an N2S3 ligand environment. The sulfur atoms are post‐translationally modified and have three different oxidation states (αCys, Cys‐SOH and Cys‐SOO−) while backbone amines account for the nitrogen ligands and are deprotonated. Theoretical calculations assume that the αCys ligand is a thiolate, making it a strong π‐donor ligand and a good a nucleophile. A critical outstanding mechanistic question is whether the formation of a transient disulfide bond is essential for catalytic turnover. Such a transient disulfide bond was proposed based on QM/MM calculations between the αCys sulfur and the sulfur of the proposed sulfenic acid cyclic intermediate. However, more recent theoretical studies is self‐inconsistent in its conclusions regarding a transient disulfide formation. To examine the role of the αCys108 ligand in catalysis, it was mutated to A, M, S, and H in the Co‐type NHase from Pseudonocardia thermophila JCM 3095 (PtNHase). ICP‐MS demonstrated reduced metal ion content for each mutant: &lt;5% (αC108A), ~44% (αC108M), ~50% (αC108S) and ~55% ( αC108H) and catalytic activity also decreased to ~0.3%, ~0.8%, ~1.6%, and ~6.7%, respectively, towards acrylonitrile. The X‐ray crystal structure of αC108A confirmed the mutation and the decreased active site metal content. Therefore, the axial thiolate is important to properly tune the electronic properties of the active site metal ion, but is not essential to catalysis. These data provide insight into the critical mechanistic question of whether the axial αCys ligand forms a transient disulfide bond during turnover.Support or Funding InformationThis work was supported by (CHE‐1808711, RCH; CHE‐1308672, BB; CHE‐1532168 BB &amp; RCH), the Todd Wehr Foundation, Bruker Biospin, and the National Institutes of Health/NIBIB National Biomedical EPR Center (P41‐EB001980)

Pelletized Cu-Ni/CePr5 catalysts for H2 purification via Water Gas Shift reaction

Water Gas Shift (WGS) reaction recently gained attraction as a purifying method to remove CO in H2 stream produced from bio-alcohols reforming for fuel cells applications. In previous works, we tested Cu-Ni samples supported on Pr promoted ceria as catalysts for WGS reaction. However, powder samples are not recommended for a scale-up process and ceria samples lack of cohesive forces to obtain a pellet. Then, supported catalysts can be an interesting alternative to study. In the present work, alumina spheres were impregnated in order to replicate the same chemical formulation of powder-state samples. It was studied the influence in catalytic performance of several textural and catalytic features such as: pellet size, active phase content and distribution, Cu:Ni ratio in bimetallic samples, and contact time. The Cu samples showed a moderate activity and the Ni ones a better performance, but tendency to generate CH4. For all catalysts, the decrease in the pellet size induced a higher CO conversion, indicating strong mass diffusion effects. Besides, it was observed that small addition of Cu to Ni samples significantly moderated the methanation reaction, but maintaining the activity. The change in active metal content slightly modified the activity and changed the selectivity, in agreement with the characterization techniques results (H2-TPR and OSC). In summary, the sample with Cu:Ni ratio equal to 1:2 with 1.5 wt%, presented a great performance, by removing 8 to 2 %v/v of CO with an acceptable contact time and high selectivity, being the most promissory catalyst for higher scale tests.

Durability analysis and degradation mechanism for an electrolytic air dehumidifier based on PEM

Electrolytic air dehumidification (vapor electrolysers) based on proton-exchange membrane (PEM) is competitive to conventional dehumidifiers, but serious degradation has been found in long-running applications. This study conducted the durability test of electrolytic dehumidifier, under continuous operation for more than 250 h. Changes in current and dehumidification rate were analyzed and compared to those for fuel cells and water electrolysers. Physicochemical and electrochemical changes of the materials before and after the test were investigated. Results show that higher applied potential or higher air humidity corresponds to a larger dehumidification amount, while performance attenuates more quickly over time. When the applied potential increased from 2 V to 4 V, the degradation rate increases from 23% to 67% at 90% air humidity. Simultaneously, the internal resistance of PEM element increased from 0.419 to 1.45 Ω and the reaction resistance changed from 1.13 to 2.17 Ω, indicating by in-situ and ex-situ EIS. By characterization analysis, it indicated that the corrosion of the anode-side catalyst IrO2 is the main reason for the long-term attenuation. The grain size of almost all IrO2 faces reduced after 250 h dehumidification, and the content of active metal of the catalyst lost by 54.3%. The dissolution rate of IrO2 also increases with increasing applied potential. Besides, there is almost no physical or chemical damage on PEM or cathode catalyst before and after the durability test. This research clarifies the micro-scale changes of the materials during long-term operation, and discloses the degradation mechanism of PEM-based electrolytic dehumidifiers.

Hydrodeoxygenation of sorbitol to gasoline-range hydrocarbons over Pt, Pd, Rh, Ru, Ni catalysts supported on tungstated alumina

Catalytic properties of the tungstated alumina (WA) supported catalysts with different nature and content of active metal (Pt, Pd, Rh, Ru, Ni) were studied in the continuous flow hydrodeoxygenation of sorbitol at a temperature of 653 K, a pressure of 4.0 MPa, and weight hourly space velocity (WHSV) of 1.0 h−1. The catalysts were characterized by N2 physical adsorption, H2-TPR, CO chemisorption, TEM, and NH3-TPD. It was found that all catalysts provide complete conversion of sorbitol with the formation of C5–C7 hydrocarbons as the main products which include n-alkanes, cycloalkanes, and isoalkanes. The yield of С5–С7 hydrocarbons after 1 h of the reaction increases from 42 to about 74 mol% in a series of catalysts: 5% Ni/WA < 0.5% Ru/WA < 0.5% Pd/WA < 0.5% Rh/WA < 0.5% Pt/WA. The calculated value of the research octane number (RON) for the С5–С7 mixture rises from ca. 62 to 80 in a series of catalysts: 0.5% Pt/WA < 0.5% Pd/WA < 0.5% Rh/WA < 5% Ni/WA < 0.5% Ru/WA. The stable yield and RON values (no less than 57 mol% and 70, respectively) of С5–С7 hydrocarbon mixture are achieved during hydrodeoxygenation over the 0.5% Pd/WA catalyst for 8 h.

Synthesis of large pore carbon-alumina supported catalysts for hydrodemetallization

This study is carried out to synthesize a supported hydrodemetallization (HDM) catalysts. The supports are prepared by mixing peptized alumina with activated carbon. The compositions of the supports (0–75 % activated carbon in alumina), the stepwise drying, and the calcination under the moderate flow of air in a rotating furnace produced supports with large pore volume, which respectively enhanced the metal storage capacity and minimized diffusion limitations of large hydrocarbon molecules (i.e., asphaltene). The presence of carbon in support also helped in reducing coke and metal depositions on pore-mouth and catalytic sites. The optimum textural and mechanical properties of the support are obtained when the carbon-alumina weight ratio is 1:1. The catalysts are synthesized by impregnating the support extrudates with low content of Mo active metal with or without Co or Fe as a promoters metals. FeMo supported catalyst showed better synergy than the CoMo and NiMo catalysts. The FeMo supported catalyst composition (10–75 wt% carbon) indicated best HDM results for an optimum pore diameter. The activity and the stability of the catalysts were evaluated using residual oil and heavy crude oil (Ku crude), which respectively have metal content (Ni and V) of 212 ppm and 567 ppm. The catalyst contains meso- macro-pores along with bimodal-type pore structure and has textural properties such as an average pore diameter of 5–1000 nm, a total pore volume of 0.3–1.5 ml/g, and moderate surface area of 50–200 m2/g.

Formate hydrogenlyase: A group 4 [NiFe]-hydrogenase in tandem with a formate dehydrogenase.

Hydrogenase enzymes are currently under the international research spotlight due to emphasis on biologically produced hydrogen as one potential energy carrier to relinquish the requirement for 'fossil fuel' derived energy. Three major classes of hydrogenase exist in microbes all able to catalyze the reversible oxidation of dihydrogen to protons and electrons. These classes are defined by their active site metal content: [NiFe]-; [FeFe]- and [Fe]-hydrogenases. Of these the [NiFe]-hydrogenases have links to ancient forms of metabolism, utilizing hydrogen as the original source of reductant on Earth. This review progresses to highlight the Group 4 [NiFe]-hydrogenase enzymes that preferentially generate hydrogen exploiting various partner enzymes or ferredoxin, while in some cases translocating ions across biological membranes. Specific focus is paid to Group 4A, the Formate hydrogenlyase complexes. These are the combination of a six or nine subunit [NiFe]-hydrogenase with a soluble formate dehydrogenase to derived electrons from formate oxidation for proton reduction. The incidence, physiology, structure and biotechnological application of these complexes will be explored with attention on Escherichia coli Formate Hydrogenlyase-1 (FHL-1).