Novel Ni–Al nanosheet catalyst with homogeneously embedded nickel nanoparticles for hydrogen-rich syngas production from biomass pyrolysis

In this work, an innovative porous Ni–Al nanosheet catalyst synthesized by a homogeneous precipitation method via urea hydrolysis is proposed for enhanced hydrogen-rich syngas production from catalytic pyrolysis of rice husk in a two-stage reactor system. The role of synthesis temperature in modulating the crystalline composition, particle size, metal dispersion as well as porous structure of resulting Ni–Al nanocomposite has been delineated. The results indicate that fine spherical NiO and metallic Ni⁰ nanoparticles are homogeneously embedded in amorphous Al₂O₃ matrix for all Ni–Al catalysts, which also have developed bimodal micro/mesoporous structure with high surface areas (513–948 m²/g). Catalytic tests show that these highly active catalysts exhibit almost ten times higher hydrogen production rate (7.74–17.39 mmol/g biomass) and H₂/CO molar ratio (1.96–2.74) than that in the absence of catalyst (0.56–1.64 mmol/g, 0.11–0.24) by tuning catalytic temperatures. The Ni–Al catalysts that with the presence of metallic Ni⁰ and developed porous structure exhibit higher catalytic activity and suppression of coke deposition through providing more active sites for catalytic cracking and reforming reactions, and rapid diffusion of intermediate products.     

Response surface optimization of syngas production from greenhouse gases via DRM over high performance Ni–W catalyst

The process parameters for dry reforming of methane (DRM) over Ni–W/Al₂O₃–MgO catalyst are optimized using response surface methodology (RSM). The Ni–W bimetallic catalyst is synthesized by co-precipitation method followed by impregnation. The catalysts are characterized by BET, XRD, FESEM, EDX and TEM; to study physicochemical properties, morphology, composition, crystallite size and deposited carbon. The effect of process parameters, i.e., reaction temperature (600^oC–800 °C) and feed gas ratio (0.5–1.5) on the CH₄, CO₂ conversions and syngas ratio are studied. A temperature of 777.29 °C with CH₄: CO₂ of 1.11 at GHSV of 36,000 cm³gm.cat^?1h^?1, delivered the CH₄ and CO₂ conversions of 87.6% and 93.3%, respectively along with H₂:CO of 1. The predicted process parameters were verified through actual experimental analysis at the optimized conditions, and results agreed with CCD of the RSM model with insignificant error. The MWCNT formed during DRM avoided catalyst deactivation and delivered stable performance over 12 h of reaction test at the optimized conditions.     

LDH-derived Ni–MgO–Al2O3 catalysts for hydrogen-rich syngas production via steam reforming of biomass tar model: Effect of catalyst synthesis methods

Steam reforming of toluene (SRT) as a model tar compound is studied on Ni–MgO–Al₂O₃ hydrotalcite synthesized by different methods: urea hydrolysis, coprecipitation, and wet impregnation. The two wet-impregnated catalysts were produced by immersing MgO–Al₂O₃ hydrotalcites synthesized by urea hydrolysis and coprecipitation in Ni²⁺ solution to produce the corresponding impregnated catalysts. Among all the catalysts, both the samples prepared by urea hydrolysis gave superior toluene conversion of ~85% and also improved the resistance to carbon deposits. The two coprecipitation catalysts had a low toluene conversion of ~63% and also produced more coke. The X-ray photoelectron spectroscopy studies showed that impregnated catalyst produced from urea hydrolysis imparted greater metal-support interaction; whereas the coprecipitation impregnation catalysts only weakly interacted with the support. The CO₂ temperature programmed desorption measurement of the reduced catalysts showed that urea hydrolysis catalysts possessed higher surface basicity as compared to coprecipitation catalysts. This high basic character aided in suppressing the coke formation. HRTEM results also revealed that urea hydrolysis produced smaller Ni⁰ particles (6–7 nm) and coprecipitation produced larger particles (10–20 nm). The excellent reforming properties of urea hydrolysis is due to smaller Ni⁰ particle size and greater surface basicity which aided in improving the catalytic performance and suppressing coke.     

Self-optimized and renewable Ni–Co alloy@Co–Co2C catalyst for higher alcohols synthesis from syngas

Higher alcohols synthesis (HAS) from syngas (CO/H₂) has attracted widespread attention, while the low selectivity and poor stability of the catalysts mainly stumbled its industrial application. In the work, Ni–Co alloy nanoparticles (NPs) derived from Co_1-xNi_xAl₂O₄ loaded on the SiO₂ with large specific surface area were prepared; and during reaction, the highly dispersed Ni–Co alloys were self-optimized to Ni–Co alloy@Co–Co₂C. Importantly, Ni–Co alloy@Co–Co₂C can be regenerated through oxidation - reduction - self-optimization process. Characteristic results indicated that the structural liberalization during the reaction process inhibited the loss of Ni, regulated and balanced the dual active sites of the catalyst and the Ni–Co alloys were regenerated after the re-oxidation and re-reduction process. The optimized catalyst exhibited excellent catalytic performance, including a high total selectivity to alcohols of 39.3% and an excellent catalytic stability at 250 °C, 3.5 MPa (H₂/CO = 2) and a space velocity of 6000 mL (g_cat h)^?1. In addition, the Ni–Co alloy@Co–Co₂C catalyst after stability test could recover its original catalytic performance after re-oxidation and re-reduction. The renewable characteristics and superior catalytic performance of Ni–Co alloy@Co–Co₂C made the catalyst to be one of the potential industrial catalysts for HAS.     

The study of bimetallic Ni–Co/cordierite catalyst for cracking of tar from biomass pyrolysis

In order to crack the tar from biomass pyrolysis, five cordierite-supported monolithic catalysts with different Ni/Co ratio were prepared by vacuum wetness impregnation. All catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), Brunauer–Emmett–Teller (BET), and scanning electron microscope (SEM). XRD and XPS characterization results show the inexistence of spinel structure such as NiAl₂O₄ and CoAl₂O₄. TPR characterization results suggest the possible formation of Ni–Co alloy. BET characterization results show that the effect of Ni/Co ratio on catalyst specific surface area is obvious. The catalytic test results show that the performance of bimetallic catalyst is better than that of monometallic catalyst. The Ni₃Co₁/cordierite catalyst exhibits the best catalytic performance among all bimetallic catalysts, its tar conversion and gas yield reach 96.4% and 1.21 Nm³/kg, respectively, at a weight hourly space velocity (WHSV) of 1.4 h⁻¹.     

Ni/SiO2 core–shell catalysts for catalytic hydrogen production from waste plastics-derived syngas

Ni/SiO₂ core–shell catalysts were prepared by deposition–precipitation method and used to produce hydrogen from waste plastics-derived syngas. The SiO₂ core synthesized by the Stöber process was used as the support. This core was synthesized using various solvents, and the effect of these solvents on the morphologies and catalytic performance of the Ni/SiO₂ core–shell catalysts was investigated. The synthesis parameters of the Ni/SiO₂ catalysts were further investigated to enhance the metal–support interaction and dispersion of Ni on the SiO₂ support. The highest catalytic activity of 181 mmol/g-h was achieved when the Ni/SiO₂ core–shell catalyst was synthesized in methanol (Ni/SiO₂–M) and reacted at 800 °C at a water-addition rate of 0.75 g-H₂O/h. The Ni/SiO₂–M catalyst, which possessed strong metal–support interaction nickel phyllosilicates, high specific area, small particle size, and homogeneous metal dispersion, exhibited the best long-term stability.     

Preparation of Ni–Cu/Mg/Al catalysts from hydrotalcite-like compounds for hydrogen production by steam reforming of biomass tar

Ni–Cu/Mg/Al bimetallic catalysts were prepared by the calcination and reduction of hydrotalcite-like compounds containing Ni²⁺, Cu²⁺, Mg²⁺, and Al³⁺, and tested for the steam reforming of tar derived from the pyrolysis of biomass at low temperature. The characterizations with XRD, STEM-EDX, and H₂ chemisorption confirmed the formation of Ni–Cu alloy particles. The Ni–Cu/Mg/Al bimetallic catalyst with the optimum composition of Cu/Ni = 0.25 exhibited much higher catalytic performance than the corresponding monometallic Ni/Mg/Al and Cu/Mg/Al catalysts in the steam reforming of tar in terms of activity and coke resistance. The catalyst gave almost total conversion of tar even at temperature as low as 823 K. This high performance was related to the higher metal dispersion, larger amount of surface active sites, higher oxygen affinity, and surface modification caused by the formation of small Ni–Cu alloy particles. In addition, the Ni–Cu/Mg/Al catalyst showed better long-term stability than the Ni/Mg/Al catalyst. No obvious aggregation and structural change of the Ni–Cu alloy particles were observed. The coke deposition on the Ni–Cu/Mg/Al catalyst was approximately ten times smaller than that on the Ni/Mg/Al catalyst, indicating good coke-resistance of the Ni–Cu alloy particles.     

Optimization of CO2 reforming of methane process for the syngas production over Ni–Ce/TiO2–ZrO2 catalyst using the Taguchi method

In the present study, Taguchi method-based design of experiment with L9 orthogonal array was implemented to optimize the process conditions for CO₂ reforming of methane over the Ni–Ce/TiO₂–ZrO₂ catalyst. The catalyst composition, catalyst reduction temperature, reaction operating temperature, and the CO₂/CH₄ ratio of the reactant gas were the control parameters. The performance index was considered as the response of the Taguchi experiment. The performance index was calculated by considering the product gas H₂/CO ratio, deactivation factor, carbon deposition, and maximum CH₄ conversion. The catalysts were prepared in two steps using the evaporation-induced self-assembly and urea deposition-precipitation methods. The catalysts were characterized in their fresh and spent stages using various techniques like X-ray diffraction, N₂-physisorption, H₂ temperature-programmed reduction, inductively coupled plasma-mass spectroscopy, Scanning electron spectroscopy, Transmission electron spectroscopy, and Thermogravimetric analysis. The results showed that the operating temperature had the principal effect on the performance index. The optimal conditions from signal/noise ratio analysis were Cat3 catalyst with Ti/Zr ratio of 1:3, catalyst reduction temperature of 600 °C, the operating temperature of 800 °C, and feed gas ratio as CO₂/CH₄ = 2. Higher Zr content in the catalyst support and the lower reduction temperature favor enhancing the performance index.     

Jet fuel production from palm oil by catalytic hydrocracking using a Ni–Mo/HY catalyst

Catalytic hydrocracking of palm oil over zeolites of HY supporting Ni and Mo (Ni–Mo/HY) catalysts was carried out to produce jet fuels. A Box–Behnken Design (BBD) followed by the Response Surface Methodology (RSM) with 17 runs was used to assess the significance of three factors: reaction temperature (°C), weight of the catalyst (%wt) used, and the reaction time (minute) required to achieve the optimum percentage of jet fuel (%jet fuel). The coefficients of determination (R²) for regression equations were 99.51%. The probability value (p < 0.05) demonstrated a very good significance for the regression model. The optimal values of variables were reaction temperature (418.85°C), the weight of the catalyst (3.16 wt%), and reaction time (119.37 min). Under the optimum conditions, % jet fuel reached 36.60%. The RSM was confirmed to sufficiently describe the range of convert palm oil into jet fuel parameters studied and provide a statistically accurate estimate of the best transform to jet fuel using Ni–Mo/HY as the catalyst. The physicochemical properties of the jet fuel were produced within the ASTM D7566 standard for jet fuel. The results proved that palm oil can be utilized as an alternative energy resource.     

Study of Ni/CeO2–ZnO catalysts in the production of H2 from acetone steam reforming

This paper reports the study of new Ni/ZnO-based catalysts for hydrogen production from substoichiometric acetone steam reforming (ASR). The effect of CeO₂ introduction is analyzed regarding the catalytic behavior and carbon deposits formation. ASR was studied at 600 °C using a steam/carbon ratio S/C = 1. Ni/xCeZnO (x = 10, 20, 30 CeO₂ wt %) catalysts showed a better performance than the bare Ni/ZnO. Ni/xCeZnO generated a lower amount and less ordered carbon deposits than Ni/ZnO. The higher the CeO₂ content in Ni/xCeZnO, the lower the amount of carbon deposits in the post-reaction catalyst. The highest H₂ production under ASR at the experimental conditions used was achieved for the Ni/xCeZnO catalysts. In-situ DRIFTS-MS experiments under ESR conditions showed different reaction pathways over Ni/20CeZnO and Ni/ZnO catalysts.     

Autothermal syngas production from model gasoline over Ni,Rh and Ni–Rh/Al2O3 monolithic catalysts

On-board reforming of liquid fuels is attractive for fuel cell-powered auxiliary power units in vehicles. In this work, monometallic Ni/Al₂O₃/cordierite, Rh/Al₂O₃/cordierite and bimetallic Ni–Rh/Al₂O₃/cordierite monolithic catalysts were prepared, characterized and tested in ATR of isooctane for syngas production. Compared to monometallic formulations, the bimetallic Ni–Rh/Al₂O₃ catalyst was active for ATR at lower temperature and H₂ production already reached the equilibrium composition in 400–550 °C temperature range. The Ni–Rh/Al₂O₃ catalyst exhibited stable performances for 140 h in ATR of isooctane at 700 °C, and was unaffected by oxidizing conditions at 700 °C. Thermoneutral reactions conditions at H₂O/C = 2 were obtained with O/C = 0.66. Carbon deposition was marginal during ATR of isooctane and no carbons whiskers were detected. Post-reaction characterizations showed that the Ni particles were small enough to prevent filamentous carbon formation, while Rh also prevented carbon film deposition by improving the gasification of adsorbed C with steam.     

Hydrogen production from carbon dioxide reforming of methane over highly active and stable MgO promoted Co–Ni/γ-Al2O3 catalyst

CoNi/Al₂O₃ and MgCoNi/Al₂O₃ catalysts are investigated for hydrogen production from CO₂ reforming of CH₄ reaction at the gas hourly space velocity of 40,000 mL g⁻¹ h⁻¹. The MgO promoted CoNi/Al₂O₃ catalyst shows much higher conversions (97% for CO₂ and 95% for CH₄ at 850 °C) than the CoNi/Al₂O₃ catalyst. In addition, the stability is maintained for 200 h in CO₂ reforming of CH₄. The outstanding catalytic activity and stability of the MgO promoted CoNi/Al₂O₃ catalyst is mainly due to the basic nature of MgO, an intimate interaction between Ni and the support, and rapid decomposition/dissociation of CH₄ and CO₂, resulting in preventing coke formation in CO₂ reforming of CH₄.     

Ni–Pt/Al nano-sized catalyst supported on TNPs for hydrogen and valuable fuel production from the steam reforming of plastic waste dissolved in phenol

In this research, titanium nanoparticles (TNPs) for Ni–Pt/Al nano-sized catalysts were prepared via the hydrothermal technique, and their catalytic performance for the polyethylene terephthalate (PET) as plastic waste and phenol steam reforming reaction was examined. Complementary characterization methods, such as BET, ICP, TEM, XRD, FTIR, NH₃-TPD, H₂-TPR, CO₂-TPD, TGA, and CHNS, were conducted to relate surface functionality and structure to the activity of catalysts. The catalytic activity and stability with ten days on stream at 700 °C were investigated. It was found that the catalyst properties such as surface area and the number of acid sites play a crucial role in catalyst activity. The feed conversion and hydrogen yield for the optimum catalyst that is Ni–Pt/Ti–Al were found to be 92% and 75%, respectively. This research has also emphasized the opportunities of this method to resolve the threat of PET plastic waste to the environment concerning the creation of valuable fuels such as benzene, toluene, styrene, methylindene, etc.     

Synthetic gas production by dry reforming of methane over Ni/Al2O3–ZrO2 catalysts: High H2/CO ratio

Alumina prepared by the sol-gel method, was impregnated with zirconia (5, 15 and 30 wt.%). Subsequently, the resulting Al₂O₃–ZrO₂ supports were impregnated with 15% Ni to obtain the Ni/Al₂O₃–ZrO₂ catalysts. The obtained catalysts were characterized by BET, SEM, XRD, H₂-TPR and TPD- CO₂. The catalytic activity was studied by means of dry reforming of methane (DRM) for syngas production. The catalysts displayed different physicochemical properties and trends of their catalytic activity as a function of the ZrO₂ content in the mixed oxide supports. For instance, ZrO₂ (5 wt %) in the catalyst, led to enhanced concentration of the medium strength basic sites and increased specific surface area, yielding thus the best performance in the DRM, with low carbon deposition after 36 h of reaction, compared with the other catalysts. This indicates that during the DRM reaction, this catalyst can provide more surface oxygen to prevent carbon deposits that could deactivate the catalyst.     

Characteristics of hydrogen production with carbon storage by CO2-rich hydrothermal alteration of olivine in the presence of Mg–Al spinel

Artificial control of olivine alteration has potential applications for both H₂ production and CO₂ reduction (by mineralization and hydrogenation). To explore methods to overcome the still-constrained olivine alteration problem, olivine + spinel alteration experiments were performed with the addition of Mg–Al spinel in CO₂-rich (0.5 M NaHCO₃) solution under hydrothermal conditions (300 °C and 10 MPa). Mg–Al spinel enhanced olivine serpentinization significantly (more than 2 times), and generation of both H₂ and CO₂ hydrogenation products was accelerated (up to 3 times) with ≥10 wt% Mg–Al spinel especially at the latter stage of the 72 h reaction.Mineral measurements revealed that more Al released from Mg–Al spinel was incorporated into Al-serpentine by the replacement of Fe with higher Mg–Al spinel content. Both Al and Fe incorporated into Al-serpentine were released as the reaction proceeded. Thus, H₂ production was elevated with the presence of a large amount Mg–Al spinel at the latter stage of the reaction. HCO₃⁻ played an important role in the promotion of Mg–Al spinel dissolution with the release of Al, which was stored in magnesite after being utilized. This study also suggests that the presence of Mg–Al spinel (5–20 wt%) in the starting mineral does not have significant influence on the total H₂ yield from olivine alteration over the entire operation period.     

High performance formic acid fuel cell benefits from Pd–PdO catalyst supported by ordered mesoporous carbon

Formic acid as a renewable fuel can be converted to clean electricity in fuel cells by high-efficient electrochemical oxidation. The conversion rate is fundamentally dictated by the synergy of interactive aspects: catalytic activity, accessibility to active sites, electron transfer, and anti-poisoning stability. For the first time, ordered mesoporous carbon (OMC) is used as the substrate for Pd–PdO catalyst for fuel cells. The unique ordered pore-channel network of OMC can enhance the spatial dispersion of Pd nanoparticles on the pore-channel wall, while the hollow pore-channel can facilitate reactant transport. Microwave and annealing treatments are found to enhance the chemical reduction and to strengthen the anchoring of Pd–PdO catalyst on OMC substrate, respectively. The OMC supported Pd–PdO catalyst (Pd–PdO/OMC) shows 1.7-fold and an order of magnitude higher mass activity and stability as compared to commercial Pd/C catalyst. For fuel cell testing, the Pd–PdO/OMC catalyst is applied to an air-breathing microfluidic fuel cell and achieves a maximum power density of 63.0 mW cm⁻², at least one-fold higher than similar previous reports.     

Hydrogen-rich gas production from oxygen pressurized gasification of biomass using a Fe–Cr Water Gas Shift catalyst

In this paper the catalytic activity of a Fe–Cr WGS catalyst is evaluated in terms of CO conversion and H₂ production. The experimental study has been carried out under realistic conditions typical of oxygen pressurized gasification of biomass. The influence of temperature, excess steam, feed gas composition and space velocity on the activity and selectivity of the catalyst for the WGS reaction is investigated. The experimental work was carried out in a micro reactor testing unit using synthetic gas feed mixtures.     

Hydrogen generation from the hydrolysis of aluminum promoted by Ni–Li–B catalyst

In this study, the high activity Ni–Li–B catalysts were fabricated through wet chemical reduction method. Their morphological structures, crystallinity, surface area and composition were examined by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method and energy-dispersive X-ray spectroscopy (EDS). The aluminum-water reaction tests were explored in the range of temperatures from 35–75 °C. It was found that water could react with aluminum to generate hydrogen gas. The yield and hydrogen generation rate were significantly increased when all prepared catalysts were added into the reaction. The Ni–Li–B (X_LiCl = 0.1 g) catalyst exhibited the highest cumulative hydrogen volume of 201.3 ml with an average hydrogen production rate of 0.50 ml min⁻¹ at 55 °C. This phenomenon could be pointed to the emergence of the micro galvanic cell formed by the Ni–Li–B, Li/Ni–Li–B, Li and Al, which accelerated aluminum to rapidly react with water.     

High purity H2 production from sorption enhanced bio-ethanol reforming via sol-gel-derived Ni–CaO–Al2O3 bi-functional materials

Catalytic steam reforming of renewable bio-oxygenates coupled with in-situ CO₂ capture is a promising option for sustainable H₂ production. The current work focuses on high purity H₂ production over Ni–CaO–Al₂O₃ bi-functional materials via sorption enhanced steam reforming of ethanol (SEESR). To ensure the uniform distribution of catalytic sites (Ni), adsorptive sites (CaO) and stabilizer (Al₂O₃) in the bi-functional materials, a citrate sol-gel synthetic route was employed. These materials were characterized by XRD, N₂ physical adsorption, SEM, TG and TPR techniques. It was revealed that the existence of CaO in bi-functional materials could not only in-situ remove CO₂, but also play the role of inhibiting the formation of harmful spinel phase. The stabilizing role of Al component against capacity decay was confirmed, whereas the presence of Ni ions had a negative effect on the cycle CO₂ uptake. The sample of Ni/Al/Ca-85.5 possessed large specific surface area, abundant porosity with fluffy morphology, and thereby, exhibited the best CO₂ sorption capacity during 20 carbonation/calcination cycles. The highest H₂ concentration of 96% was obtained through the SEESR during the pre-breakthrough period when the Ni/Al/Ca-85.5 was employed. Over the optimized bi-functional material, the effect of operating conditions on the SEESR was investigated and the results indicated that temperature of 600 °C, reaction liquid space velocity of 0.05 ml/min and steam/ethanol ratio of 4 were the suitable conditions. After 10 cycles, the bi-functional material of Ni/Al/Ca-85.5 also showed the best performance, with a H₂ purity of about 90% and pre-breakthrough time of 18 min, conforming the high potential of this material for SEESR process.     

Biogas reforming for hydrogen-rich syngas production over a Ni–K/Al2O3 catalyst using a temperature-controlled plasma reactor

Plasma-enhanced catalytic biogas reforming for hydrogen-rich syngas production over a Ni–K/Al₂O₃ catalyst was investigated using a tabular dielectric barrier discharge non-thermal plasma reactor. To better understand the plasma catalysis synergy at elevated temperatures, we compared different reaction modes: plasma catalysis, plasma alone, and catalysis alone in a reaction temperature range of 160–400 °C. The combination of Ni–K/Al₂O₃ and plasma produced synergistic effects. Notably, the plasma-catalytic synergy was temperature-dependent and varied at different reaction temperatures. Using plasma catalysis, the maximum conversion of CH₄ and CO₂ (31.6% and 22.8%, respectively) was attained over Ni–K/Al₂O₃ at 160 °C, while increasing the reaction temperature to 340 °C noticeably enhanced the H₂/CO ratio to 2.71. Moreover, compared to plasma-catalytic biogas reforming at 160 °C, increasing the reaction temperature to 400 °C suppressed biogas conversion with dramatically reduced coke formation on the Ni–K/Al₂O₃ surface from 6.81 wt% to 3.37 wt%.