High specific surface area supports for highly active Rh catalysts: Syngas production from methane at high space velocity

A series of high specific surface area mesoporous supports (CeO₂, CeO₂-Al₂O₃, and Al₂O₃) were synthesized by the surfactant-assisted precipitation method using cetyltrimethylammonium bromide (CTAB) as template. Highly dispersed Rh-based catalysts were prepared by the wetness impregnation technique. The physico-chemical properties of the as-prepared supports and catalysts were investigated by N₂-physisorption, CO-chemisorption, XRD, and H₂-TPR measurements. Catalytic performance was evaluated towards the methane steam reforming (MSR) reaction up to 300 h of time-on-stream varying temperature (700–800 °C), steam-to-carbon (S/C = 2–3), and space velocity (88–200 SL·g_cat^?1·h^?1); turnover frequencies were calculated at each reaction condition. All catalysts exhibited high activity strictly connected with high specific surface area (105–325 m² g^?1) and metal dispersion (34.3–84.0%). Significant enhanced stability was observed for Al₂O₃-containing catalysts towards the MSR reaction at high space velocity.     

Thermocatalytic decomposition of methane over mesoporous Ni/xMgO·Al2O3 nanocatalysts

This paper describes a facile method to produce mesoporous nanostructure Ni/Al₂O₃, Ni/MgO, and Ni/xMgO.Al₂O₃ (x: MgO/Al₂O₃ molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N₂ adsorption/desorption, hydrogen temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al₂O₃ molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m² g^?1. The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al₂O₃ catalyst calcined at 600^οC possessed an acceptable methane conversion (～60%) under the harsh reaction conditions (GHSV = 48000 (mL h^?1 g_cat^?1)).     

Highly efficient Co/NC catalyst derived from ZIF-67 for hydrogen generation through ammonia decomposition

Small-size cobalt nanoparticles (NPs) distributed on nitrogen doped carbon support (Co/NC-X) were prepared by pyrolysis of ZIF-67 at various temperatures (X = 500, 600,700 and 800 °C) in nitrogen atmosphere and utilized as catalysts for hydrogen production through ammonia decomposition. Characterizations of the catalysts including XRD, HRTEM, XPS, H₂-TPR, CO₂-TPD, etc., were conducted for structure analysis. The N–C plate obtained from pyrolysis was coated with Co NPs to hinder its aggregation, which made the Co NPs dispersed evenly and increased their dispersion. The calcination temperature and the strong base of the support can adjust the strength of Co–N bond. The activity of the Co/NC-X catalysts is attributed to the high content of Co⁰ and the moderate Co–N bond strength. The ammonia decomposition activity of Co/NC-X catalysts in this paper is higher than many reported Co-based catalysts. Co/NC-600 catalyst demonstrates an ammonia conversion of 80% at 500 °C with a space velocity of 30,000 ml g_cat^?1 h^?1, corresponding to a hydrogen production rate of 26.8 mmol H₂ g_cat^?1 min^?1. The work provides insight for the development of highly active cobalt-based catalysts for hydrogen production through ammonia decomposition.     

Mechanistic insights into methanol steam reforming over a ZnZr oxide catalyst with improved activity

Methanol steam reforming (MSR) holds great potential for mobile hydrogen production, but it still requires an active and stable catalyst. In this work, we report a high-performance ZnZr-0.5 composite oxide catalyst for this reaction, with a hydrogen production rate of 2.80 mol·g_cat^?1·h^?1 and CO₂ selectivity of 99.6% at a methanol space velocity of 22,762 mL·g_cat^?1·h^?1. It also exhibits superior long-term durability in the TOS test for more than 100 h. Such good activity results from a synergistic effect of ZnO–ZrO₂ dual sites. ZrO₂ is capable of stabilizing and storing more CH₃O1 and HCOO1 intermediates while ZnO is in charge of the dehydrogenation of these key intermediates. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemisorption results reveal that the MSR reaction experiences successively the hydrolysis of methyl formate and dehydrogenation of formate. More importantly, it is found that H₂O significantly promotes the dehydrogenation of HCOO1 intermediate by directly participating in this reaction from pulse chemisorption experiments.     

Partial oxidation of dimethyl ether by air into synthesis gas over Pt- and Rh/Ce0.75Zr0.25O2–δ catalysts

Dimethyl ether partial oxidation (DME PO) by air was studied over composite oxide Ce_0.75Zr_0.25O₂ supported Pt and Rh catalysts at temperatures 300–650 °C under atmospheric pressure, WHSV = 10 L·g_cat⁻¹·h⁻¹ and DME/O₂ molar ratio of 2. The BET, XRD, TEM and TPO techniques were used for catalyst characterization. Thermodynamic equilibrium product distribution of DME PO was calculated and used as reference data for interpreting the experimental results. Both catalysts demonstrated stable performance and coking resistance at DME PO. At 650 °C the catalysts provided complete conversion of DME and О₂ into a gas mixture of composition close to the thermodynamic equilibrium one. Synthesis gas productivity was >10 L·g_cat⁻¹·h⁻¹, its concentration in the outlet gas mixture exceeded 50 vol % that is quite suitable for solid oxide fuel cell feeding applications.     

Syngas production by steam and oxy-steam reforming of biogas on monolith-supported CeO2-based catalysts

In this study, the syngas production by steam reforming (SR) and oxy-steam reforming (OSR) of clean biogas over cordierite monoliths (400 cpsi) lined with Ni, Rh, or Pt on CeO₂ catalyst was deeply investigated. Structured catalysts were prepared by using an alternative method to traditional washcoating based on the combination of the solution combustion synthesis (SCS) with the wetness impregnation (WI) technique. TEM and SEM analysis were used to study the morphology of the catalytic layer and to determine its thickness, while the quality of the coating in terms of adhesion on the monolith was evaluated by ultrasonic treatment in isopropyl alcohol solution. The performance and the stability of the structured catalysts were investigated at different process parameters, namely temperature (700–900 °C), steam-to-carbon (S/C = 1–5) and oxygen-to-carbon (O/C = 0.1–0.2) molar ratios, and weight space velocity (WSV = 30,000–250,000 NmL g_cat^?1 h^?1). The SCS + WI deposition method allowed obtaining a uniform and thin coated layer with high mechanical strength. The following order of activity was exploited: Rh > Pt > Ni for biogas SR and Rh > Pt ≈ Ni for biogas OSR. The Rh-based catalyst exhibited higher activity and long-lasting stability towards biogas SR and OSR reactions for syngas production.     

Composition dependent activity of Fe1−xPtx decorated ZnCdS nanocrystals for photocatalytic hydrogen evolution

In this work, ZnCdS nanoparticles (NPs) were decorated with FePt alloy, forming nanocomposites via ethylene glycol reduction method. The photocatalytic H₂ production of the Fe_1?xPt_x–ZnCdS NPs was studied by changing the composition and weight percentage of Fe_1?xPt_x alloy in the nanocomposites under visible light (λ ≥ 420 nm) irradiation. The results showed that the hydrogen production rate of Fe_1?xPt_x–ZnCdS NPs had a significant enhancement over the pure ZnCdS (740 μmol g^?1 h^?1). The activity of the nanocomposites was dependent on the composition of Fe_1?xPt_x alloy and the highest hydrogen production rate of 2265 μmol g^?1 h^?1 was achieved by the 0.5 wt% Fe_0.3Pt_0.7–ZnCdS nanocomposites, which was even better than that of 0.5 wt% Pt–ZnCdS (1626 μmol g^?1 h^?1) under the same condition. This study highlights the significance of Pt base alloys as new cocatalysts for the development of novel composite photocatalysts.     

The effect of barium-promoted for microsphere Ru/CeO2 catalysts in ammonia synthesis

In this essay, the effect of the morphology of the CeO₂ support and the Ba promoter on the ammonia synthesis reaction was studied. CeO₂ support with {110} and {100} crystal planes and more oxygen vacancies enhanced the catalytic activity of ammonia synthesis. The relatively uniform microspheres structure CeO₂ support (CeO₂-MS) with {110} and {100} crystal planes was synthesized. The structural functions of the as-synthesized CeO₂ support for the Ru-based catalyst were investigated in the ammonia synthesis reaction. The results of catalytic performance showed that the catalytic activity of 2.5%Ru/CeO₂-MS catalyst reached 8940 μmol· g^?1· h^?1 at 450 ℃, 3.8 MPa, H₂/N₂ = 3 (60 mL?min^?1), which is higher nearly 2.5 times than the 2.5%Ru/CeO₂-commercial (CeO₂-C). And the catalytic activity of catalysts increased with the increase of reaction temperature. The activity of 6%Ba-2.5%Ru/CeO₂-MS (24000 μmol· g^?1· h^?1) catalyst increased about 268% than that of catalyst without addition of Ba. Their physical and chemical properties were characterized by XRD, BET, HRTEM, H₂-TPR, H₂-TPD, and XPS analyses. Our results indicate that the 2.5%Ru/CeO₂-MS catalyst and catalysts involving promoters (Cs, K, and Ba) exhibit significant support-morphology-dependent catalytic activity for ammonia synthesis.     

Steam reforming and oxidative steam reforming for hydrogen production from bioethanol over Mg2AlNiXHZOY nano-oxyhydride catalysts

Mg₂AlNi_XH_ZO_Y nano-oxyhydrides formation is evidenced during pre-treatment in H₂ at 450 °C of Mg₂AlNi_XO_Y nano-compounds leading to highly performant catalysts in ethanol conversion and H₂ formation, particularly at low temperature, through catalytic steam reforming (SRE) and oxidative steam reforming (OSRE). Total conversion of ethanol is obtained in SRE and OSRE with high stability. A higher production of H₂ (60 L h^?1 g_cat^?1) can be achieved at a reaction temperature of 300 °C in OSRE conditions compared to SRE (10 L h^?1 g_cat^?1) mainly because of a beneficial use of a high concentration of ethanol (14 mol%) in presence of O₂. Moreover, carbon formation is decreased and a much lower input of energy of 50 °C is used to get a temperature of 300 °C when O₂ is added. Different physico-chemical characterizations and in particular in H₂ (TPR, H₂-XRD, INS) and after tests allow to conclude that the presence of Ni²⁺ cations in strong interaction with other cations, anionic vacancies and hydride species on and inside the solid play an important role in the catalytic performance (conversion and selectivity) and stability.     

One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V₂O₅) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V₂O₅, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V₂O₅/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na₂SO₄ solution. Remarkably, V₂O₅/PPy/GO nanocomposite shows a specific capacitance of 750 F g^?1 at a current density of 5 A g^?1, which is far better than PPy (59.5 F g^?1), V₂O₅/PPy (81.5 F g^?1) and PPy/GO (344.5 F g^?1). Furthermore, V₂O₅/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V₂O₅ can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V₂O₅/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg^?1 at a power density of 3600 W kg^?1, and a maximum power density of 13680 W kg^?1 at an energy density of 22.8 W h kg^?1.     

Cobalt nanoparticles supported on magnetic core-shell structured carbon as a highly efficient catalyst for hydrogen generation from NaBH4 hydrolysis

A novel recyclable cobalt nanocatalyst, supported on magnetic carbon with core-shell structure, was successfully synthesized by using wetness impregnation-chemical reduction method for hydrogen generation from hydrolysis of NaBH₄. The resultant nanocomposite was characterized to determine the structural and physical-chemical properties by a series of analytical techniques such as FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy-dispersive X-ray spectroscopy), TEM (transmission electron microscopy), etc. The results demonstrated that amorphous cobalt nanoparticles were homogeneously surrounded on the surface of the support due to having abundant hydrophilic groups (such as aldehyde and hydroxyl groups) on the surface of carbon layer for the effective immobilization of metal ions. The supported catalyst showed superior catalytic performance towards the hydrolysis reaction of NaBH₄ at room temperature. The total rate of hydrogen generation and activation energy were calculated to be 1403 ml H₂ g_cat^?1 min^?1 and 49.2 kJ mol^?1, respectively, which were comparable to the values of most cobalt-based catalyst reported for hydrogen production from hydrolysis of NaBH₄. Additionally, reusability test revealed that the hydrogen in NaBH₄ substrate could be completely released within 25 min with a minimum hydrogen generation rate of 832 ml H₂ g_cat^?1 min^?1 even after five runs of hydrolytic reaction, implying the as-prepared Co/Fe₃O₄@C composite could be considered as a promising candidate catalyst for portable hydrogen fuel system such as PEMFC (proton exchange membrane fuel cells).     

Selection of metabolic pathways for continuous hydrogen production under thermophilic and mesophilic temperature conditions in anaerobic fluidized bed reactors

This study evaluated the influence of hydraulic retention time (HRT) on hydrogen (H₂) production in anaerobic fluidized bed reactors at mesophilic (30 °C, AFBR-M) and thermophilic (55 °C, AFBR-T) temperatures. Reactors were fed sucrose-based synthetic wastewater (5000 mg chemical oxygen demand·L^?1) in the HRT of 8, 6, 4, 2, or 1 h. H₂ production rate increased from 67.8 ± 14.8 to 194.9 ± 57.0 ml H₂·h^?1 L^?1 (AFBR-T) and from 72.0 ± 10.0 to 344.4 ± 74.0 mL H₂·h^?1·l^?1 (AFBR-M) when HRT decreased from 8 to 1 h. Maximum H₂ yields for AFBR-T and AFBR-M were 1.93 ± 0.21 and 2.68 ± 0.48 mol H₂·mol^?1 sucrose, respectively. The main metabolites were acetic acid (31.3%–41.5%) and butyric acid (10.2%–20.7%) (AFBR-M) and acetate (20.1%–39.3%) and ethanol (14.3%–29.9%) (AFBR-T). Denaturing gradient gel electrophoresis profiles revealed selective enrichment of microbial populations responsible for H₂ production by the aceto-butyric route (AFBR-M) and ethanol-type fermentation (AFBR-T).     

Bioethanol production from corn stalk juice using Saccharomyces cerevisiae TISTR 5020

This study aimed to use sweet corn hybrid hi-brix53 stalk juice for bioethanol production, to give a solution to the growing problem of food vs. fuel and to utilize waste for cheaper production. Hi-brix 53 stalk juice contained 112.07 ± 2.99 g L^?1 of total sugars and 21.83 ± 1.09 g L^?1 of reducing sugars. Through fermentation (24–120 h) using yeast (Saccharomyces cerevisiae), it produced 6.01% (v/v) bioethanol. The final ethanol produce (g L^?1) yield efficiency and volumetric ethanol productivity were at the highest at 24 h with 47.87 L^?1, 87.62% and 1.97 ± 0.06 (g L^?1 h^?1). These results suggest that hi-brix 53 stalk juice is an ideal substrate for bioethanol production.     

Performance of batch solid state fermentation for hydrogen production using ground wheat residue

Ground wheat (21 g) was subjected to batch solid state dark fermentation for bio-hydrogen production. Clostridium acetobutylicum (B-527) was used as the culture of dark fermentation bacteria at mesophilic conditions. Effects of moisture content on the rate and yield of bio-hydrogen formation were investigated. The highest CHF (1222 ml), hydrogen yield (63 ml H₂ g^?1 starch), formation rate (10.64 ml H₂ g^?1 starch h^?1) and specific hydrogen formation rate (0.28 ml H₂ g^?1 biomass h^?1) were obtained with a moisture content of 80%. Nearly complete starch hydrolysis and glucose fermentation were achieved with more than 80% moisture content and the highest substrate conversion rate (21.9 mg L^?1 h^?1) was obtained with 90% moisture content at batch solid state fermentation producing volatile fatty acids (VFA) and H₂.     

Insights into the effect of catalyst loading on methane steam reforming and controlling regime for metallic catalytic monoliths

The influence of Ru/LaAl₂O₃ catalyst loading (100–200 mg) was investigated over high cell density Fecralloy^® monoliths (461 cpsi, 1367 cpsi) for methane steam reforming (SMR). A uniform and well-attached catalyst layer was developed by in-situ washcoating method and the developed catalysts were analyzed by using various physico-chemical characterization techniques. The results confirmed the impact of catalyst loading on the geometric and hydraulic properties of monoliths, and methane conversion was improved by increasing both the catalyst loading and cell density. As per characteristic time analysis, no external and washcoat diffusion regimes were observed and SMR was found to be in kinetic controlling regime. The methane conversion was still limited by the amount of catalyst (200 mg) deposited onto the monoliths (40.9 μm for 461 cpsi, 26.9 μm for 1367 cpsi) which demonstrated the potential to deposit more catalyst up to the transition point of washcoat diffusion limitations. For same washcoat thickness of ～20.6 μm, the higher cell density 1367 cpsi monolith showed better catalytic activity towards SMR as compared to 461 cpsi monolith and this improvement is more prominent at lower temperature with a value of 13.6% higher methane conversion at 600 °C, WHSV = 55 NL h^?1 g_cat^?1 and S/C = 3.0.     

Chitosan-mediated Co–Ce–B nanoparticles for catalyzing the hydrolysis of sodium borohydride

Highly dispersed Co–Ce–B nanoparticles supported on chitosan-derived carbon (Co–Ce–B/Chi–C) were synthesized through chemical reduction and carbonization. The morphology and microstructure of the Co–Ce–B/Chi–C nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller adsorption analysis. This nanocomposite had uniform morphology and large surface area, and it showed high catalytic activity for NaBH₄ hydrolysis and good cycle stability. Compared with unsupported Co–Ce–B particles, this nanocomposite showed greatly increased catalytic activity for NaBH₄ hydrolysis. A remarkably high hydrogen generation rate of 4760 mL^?1 min^?1 g^?1 at 30 °C was achieved with low activation energy of 33.1 kJ mol^?1. These results indicate that the Co–Ce–B/Chi–C nanocomposite is a promising catalyst for on-demand hydrogen generation via NaBH₄ hydrolysis.     

Biomolecule-assisted hydrothermal synthesis of ZnxCd1−xS nanocrystals and their outstanding photocatalytic performance for hydrogen production

To achieve scalable applications in solar hydrogen production, it is necessary to develop visible-light-responsive photocatalysts that are highly efficient, cost-effective, stable and environmentally-benign. Here narrow bandgap Zn–Cd–S solid solution photocatalysts (E_g = 2.11–2.53 eV) were prepared via a facile and green hydrothermal strategy under mild conditions. Amazingly, over the naked Zn_0.5Cd_0.5S photocatalyst, an extraordinarily high H₂ production activity in Na₂S–Na₂SO₃ aqueous solution is achieved up to 18.3 mmol h^?1 g^?1 with an apparent quantum efficiency of 73.8% per 50 mg under 420 nm light irradiation, which, to our knowledge, outperforms cocatalyst-free metal sulfide photocatalysts previously reported to date. Such super high performance arises from the enhanced visible-light-absorption capacity, suitable conduction and valence band potential together with the facilitated charge transport in Zn–Cd–S solid solutions. This work may open an avenue for the green preparation of inexpensive photocatalysts for solar H₂ production.     

Preparation of Cu0.1-xNixCe0.9O2-y catalyst by ball milling and its CO catalytic oxidation performance

A series of Cu_0.1-xNi_xCe_0.9O_2-y catalysts with different Cu/Ni molar ratios were prepared by the ball milling method. The obtained catalytic materials were characterized by XRD, H₂-TPR, BET, XPS and Ramen and the effects of different Cu/Ni content on the structure, properties and CO catalytic oxidation performance of the catalysts were explored. The results evidenced the formation of Cu–Ni–Ce mixed oxide solid solution in all ternary catalysts. In addition, there is a synergistic interaction between Cu and Ni in ternary catalysts, resulting in more oxygen vacancies and improved reduction performance, and hence demonstrating better CO catalytic oxidation activity in the ternary catalysts than binary ones. Under a GHSV of 60000 mL·g_cat⁻¹·h⁻¹, the required reaction temperature for reaching less than 10 ppm CO is lowed from 160 °C with Cu_0·1Ce_0·9O_2-y to 130 °C with Cu_0·07Ni_0·03Ce_0·9O_2-y.     

Modelling of the ethanol steam reforming over Rh-Pd/CeO2 catalytic wall reactors

Existing literature data have been used to model the steam reforming of ethanol on catalytic honeycombs coated with Rh-Pd/CeO₂, which have shown an excellent performance and robustness for the production of hydrogen under realistic conditions. In this article, a fully 3D non-isothermal model is presented, where the reactions of ethanol decomposition, water gas shift, and methane steam reforming have been modelled under different operational pressures (1–10 bar) and temperatures (500–1200 K) at a steam to carbon ratio of S/C = 3 and a space time of W/F between 2·10⁻³ and 3 kg h L_liq⁻¹. According to the modelling results, a maximum hydrogen yield of 80% is achieved at a working temperature of 1150 K and a pressure of 4 bar at S/C = 3.     

Synthesis of polymer supported Ni (II)-Schiff Base complex and its usage as a catalyst in sodium borohydride hydrolysis

Influence of using as catalysis, Ni-Schiff Base complex which we previously synthesized [1] used to support with amberzyme oxirane resin (A.O.R.) polymer for increasing the catalytic activity in NaBH₄ hydrolysis reaction, to hydrogen generation was studied. The prepared catalyst was characterized by using SEM, XRD, BET, FT-IR analyze technique. Polymer supported Ni-Schiff Base complex catalyzed NaBH₄ hydrolysis reaction was investigated depending on concentration of NaBH₄, concentration of NaOH, temperature, percentage of Ni complex in total polymer supported Ni-Schiff Base complex and amount of catalyst factors. The maximum hydrogen production rate from hydrolysis of sodium borohydride with nickel-based complex catalyst compared to the pure nickel catalyst is increased from 772 mL H₂·g^?1 cat.·min^?1 to 2240 mL H₂ g^?1 cat.·min^?1 [1], and with supported amberzyme oxirane resin polymer this nickel based complex catalyst was increased to 13000 mL H₂·g^?1 cat.·min^?1 at 30 °C. The activation energy of complex catalyzed NaBH₄ hydrolysis reaction was found as 25.377 kJ/mol. This work also includes kinetic information for the hydrolysis of NaBH₄.