Coke-resistance enhancement of mesoporous γ-Al2O3 and MgO-supported Ni-based catalysts for sustainable hydrogen generation via steam reforming of acetic acid

Highly ordered mesoporous γ-Al₂O₃ particles and MgO materials were synthesized by evaporation induced self-assembly (EISA) and template-free hydrothermal co-precipitation routes, respectively. Ni, Ni–MgO, and Ni–La₂O₃-containing catalysts were prepared using a wet-impregnation method. The synthesized catalysts were characterized by N₂ adsorption–desorption, XRD, SEM-EDS, DRIFTS, XPS, TGA-DTA, and Raman spectroscopy analysis. The mesoporous γ-Al₂O₃ catalyst support exhibited a high surface area of 245 m²/g and average pore volume of 0.481 cm³/g. The DRIFTS results indicate the existence of large Lewis's acid regions in the pure γ-Al₂O₃ and metal-containing catalysts. Catalytic activity tests of pure materials and metal-containing catalysts were carried out at the reaction temperature of 750 °C and a feed molar ratio of AA/H₂O/Ar:1/2.5/2 over 3 h. Complete conversion of acetic acid and 81.75% hydrogen selectivity were obtained over the catalyst 5Ni@γ-Al₂O₃. The temperature and feed molar ratio had a noticeable impact on H₂ selectivity and acetic acid conversion. Increasing the water proportion in the feed composition from 2.5 to 10 considerably improved the catalytic activity by increasing hydrogen selectivity from 81.75% to 91%. Although the Ni-based γ-Al₂O₃-supported catalysts exhibited higher activity performance compared to the Ni-based MgO-supported catalysts, they were not as resistant to coke formation as were MgO-supported catalysts. The introduction of MgO and La₂O₃ into the Ni@γ-Al₂O₃ and Ni@MgO catalysts' structures played a significant role in lowering the carbon formation (from 37.15% to 17.6%–12.44% and 12.17%, respectively) and improving the thermal stability of the catalysts by decreasing the agglomeration of acidic sites and reinforcing the adsorption of CO₂ on the catalysts' surfaces. Therefore, coke deposition was reduced, and catalyst lifetime was improved.     

Catalytic steam reforming of bio-oil aqueous fraction for hydrogen production over Ni–Mo supported on modified sepiolite catalysts

Hydrogen will be an important energy carrier in the future and hydrogen production has drawn a great deal of attention to its advantages in efficiency and environmental benefit. Catalytic steam reforming in this study was carried out in a fixed bed tubular reactor with sepiolite catalysts. Sepiolite catalysts modified with nickel (Ni) and molybdenum (Mo) were prepared using the precipitation method. Influential parameters such as temperature, catalyst, steam to carbon ratio (S/C), the feeding space velocity (WHSV), reforming length, and activity of catalyst were investigated and the yields of H₂, CO, CH₄, and CO₂ were obtained. The result of this experiment shows that the acidified sepiolite catalyst with addition of the Ni and Mo greatly improves the activities of catalyst and effectively increases the yield of hydrogen. The favorable reaction condition is as follows: reaction temperature is 700–800 °C; S/C is 16–18; the feeding space velocity is 1.5–2.2 h⁻¹, respectively.     

Ni–Co bimetallic MgO-based catalysts for hydrogen production via steam reforming of acetic acid from bio-oil

Acetic acid (AC) is a representative compound of bio-oil via fast pyrolysis of biomass, and can be processed for hydrogen production via steam reforming (SR). In the current work, the Ni_xCo_1−xMg₆O_7±δ (x = 0–1) bimetallic catalysts were prepared via co-precipitation and impregnation, and tested in SR of AC. The reaction results indicate that the monometallic catalysts were deactivated obviously in SR, while the Ni_0.2Co_0.8Mg₆O_7±δ bimetallic catalyst performed better in both activity and stability: not only the conversion of AC remained stable near 100%, but also the H₂ yield maintained stable near 3.1 mol-H₂/mol-AC. The results of XRD, BET, XPS, TG and TEM indicate that the high catalytic performance of the Ni_0.2Co_0.8Mg₆O_7±δ catalyst can be attributed to 1) resistance to oxidation of active metals, 2) resistance to coking, and 3) stability of structure and electronic properties.     

Hydrogen production by sorption-enhanced steam reforming of acetic acid over Ni/CexZr1−xO2-CaO catalysts

The production of high purity hydrogen via the sorption-enhanced steam reforming of acetic acid, a model compound of bio-oil, was investigated in this work. A bi-functional catalyst with stable catalytic activity and CO₂-capture ability, Ni/Ce_xZr_1−xO₂-CaO, was prepared by a sol–gel method and characterized in details by BET, XRD, TPR and SEM-EDX analytic techniques. The characterization of these materials showed that the catalysts were mainly composed of Ni, Ce_xZr_1−xO₂ and CaO. As CaO loading increased, a new species, CaZrO_3, with a perovskite structure was formed. The presence of CaZrO₃ in the catalysts acted as a barrier to CaO grain growth at high temperatures and thus improved the CO₂-capture stability. These catalysts exhibited good CO₂ sorption capacity in 15 consecutive carbonation–calcination cycles, even at a high calcination temperature of 900 °C. Particularly, in case of the Ni/CZC-2.5 catalyst, 98% high purity H₂ could be obtained during the prebreakthrough stage when the catalysts were tested in the SESR of acetic acid at 550 °C with an S/C ratio of 4. In addition, high hydrogen purity was maintained over 15 cyclic reaction-calcination operations, which was mainly attributed to the uniform distribution of Ni, CaO, Ce_xZr_1−xO₂ and CaZrO₃ in the catalysts. These results indicated the great potential of the SESR technique for hydrogen production from bio-oil.     

Effect of La2O3 replacement on γ-Al2O3 supported nickel catalysts for acetic acid steam reforming

The effect of replacement of γ-Al₂O₃ by La₂O₃ was studied on Ni catalysts for hydrogen production via acetic acid steam reforming. The La/(La + Al) weight ratio ranged from 0 to 1 in the catalyst support prepared by co-precipitation method. Over the Ni/La-3Al catalyst (the La/(La + Al) weight ratio at 0.25), the carbon conversion and hydrogen yield reached 100% and 72.72%, respectively, which was obviously higher than other catalysts at 700 °C, S/C = 1 and LHSV = 10 h^?1. The effect of S/C, LHSV and stability test were studied in detail over Ni/La-3Al catalyst, whose high activity maintained for more than 30 h.     

Agglomerated Co–Cr/SBA-15 catalysts for hydrogen production through acetic acid steam reforming

Hydrogen produced from renewable resources is becoming interesting as an alternative to conventional fossil fuels. Co-based catalysts have been reported for their active role in steam reforming of acetic acid as the main model compound of bio-oil aqueous fraction. In the present work, a series of Co–Cr/SBA-15 extrudates were prepared by varying the binder (bentonite) content and particle size in order to get catalyst particles suitable to be used in a steam reformer at industrial scale. Catalysts were characterized by N₂ physisorption, ICP-AES, TEM, SEM, XRD and H₂-TPR. The physicochemical characterization results showed that no remarkable changes occurs after the extruding process of the powdered sample, except for the particle size and mechanical strength. Acetic acid steam reforming tests were done at 600 °C and WHSV = 30.1 h⁻¹ varying the feed flow rate and the catalysts particle size in order to study the influence of internal and external diffusion limitations. Extruded particles with an effective diameter of 1.5 mm and 30 wt% of bentonite get similar conversion and hydrogen selectivity than powder sample. Besides, the agglomerated catalysts are also stable up to 12 h of TOS.     

Hydrogen production from steam reforming of bioethanol using Cu/Ni/K/γ-Al2O3 catalysts. Effect of Ni

Hydrogen to be used as a raw material in fuel cells or even as a direct fuel can be obtained from steam reforming of bioethanol. The key aim of this process is to maximize hydrogen production, discouraging at the same time those reactions leading to undesirable products, such as methane, acetaldehyde, diethyl ether or acetic acid, that compete with H₂ for the hydrogen atoms. Cu–Ni–K/γ-Al₂O₃ catalysts are suitable for this reaction since they are able to produce acceptable amounts of hydrogen working at atmospheric pressure and a temperature of 300°C. The effect of nickel content in the catalyst on the steam-reforming reaction was analyzed. Nickel addition enhances ethanol gasification, increasing the gas yield and reducing acetaldehyde and acetic acid production.     

Catalytic steam reforming of glycerol over Ni–La2O3–CeO2/SBA-15 catalyst for stable hydrogen-rich gas production

Ni-based catalysts (Ni, Ni–La₂O₃, and Ni–La₂O₃–CeO₂) on mesoporous silica supports (SBA-15 and KIT-6) were prepared by an incipient wetness impregnation and tested in glycerol steam reforming (GSR) for hydrogen-rich gas production. The catalysts were characterized by the N₂-physisorption, TPD, X-ray diffraction (XRD), SEM-EDS, and TEM techniques. N₂-physisorption results of calcined catalysts highlight that adding of La₂O₃ increased surface area of the catalyst by preventing pore mouth plugging in SBA-15, which was frequently observed due to the growth of NiO crystals. A set of GSR experiments over the catalysts were performed in an up-flow continuous packed-bed reactor at 650 °C and atmospheric pressure. The highest hydrogen concentration of 62 mol% was observed with a 10%Ni–5%La₂O₃ –5%CeO₂/SBA-15 catalyst at a LHSV of 5.8 h⁻¹. Adding of CeO₂ to the catalyst appeared to increase catalytic stability by facilitating the oxidative gasification of carbon formed on/near nickel active sites of Ni–La₂O₃–CeO₂/SBA-15 and Ni–La₂O₃–CeO₂/KIT-6 catalyst during the glycerol steam reforming reaction.     

Ni/Y2O3–ZrO2 catalyst for hydrogen production through the glycerol steam reforming reaction

In the study presented herein, the catalytic activity and stability of a Ni catalyst supported on Y₂O₃–ZrO₂ was examined for the first time in the glycerol steam reforming reaction and compared with a Ni/ZrO₂. The addition of Y₂O₃ stabilized the ZrO₂ tetragonal phase, increased the O₂ storage capacity of the support and the medium strength acid sites of the catalyst, and although the Ni/Zr catalyst had a higher concentration of basic sites, the Ni/YZr presented more stable monodentate carbonates. Moreover, the Ni/YZr had substantially higher Ni surface concentration and smaller Ni particles. These properties influence the gaseous products’ distribution by increasing the H₂ yield and selectivity and preventing the transformation of CO₂ to CO, by inhibiting the reverse water gas shift (RWGS) reaction from taking place. For both catalysts the main liquid products identified were allyl alcohol, acetaldehyde, acetone, acrolein, acetic acid and acetol; these were subsequently quantified. The time-on-stream experiments showed that the Ni/YZr was more stable during reaction and had a higher H₂ yield after 20 h (2.17 in comparison to 1.50 mol H₂/mol C₃H₈O₃, for the Ni/Zr). Extensive investigation of the carbon deposits showed that although lower amounts of coke were deposited on the Ni/Zr catalyst, these structures were more graphitic in nature and had fewer defects, which means they were harder to oxidize. Moreover, transmission electron microscopy (TEM) analysis showed that sintering of Ni nanoparticles during the reaction was significant for the Ni/Zr catalyst, as the mean particle diameter increased from an initial value of 48.2 to 67.9 nm, while it was almost absent on the Ni/YZr catalyst (the mean particle diameter increased from 42.1 to 47.4 nm).     

Ni/Pd-promoted Al2O3–La2O3 catalyst for hydrogen production from polyethylene terephthalate waste via steam reforming

Ni/Pd-co-promoted Al₂O₃–La₂O₃ catalysts for selective hydrogen production from polyethylene terephthalate (PET) plastic waste via steam reforming process has been investigated. The catalysts were prepared by impregnation method and were characterized using XRD, BET, TPD-CO₂, TPR-H₂, SEM, TGA and DTA. The results showed that Ni-Pd-co-impregnated Al₂O₃–La₂O₃ catalyst has excellent activity for the production of hydrogen with a prolong stability. The feed conversion of 87% was achieved over 10% Ni/Al₂O₃ catalyst which increased to 93.87% in the case of 10% Ni-1% Pd/Al₂O₃–La₂O₃ catalysts with an H₂ fraction of 0.60. The catalyst performance in term of H₂ selectivity and feed conversion was further investigated under various operating parameters, e.g., temperatures, feed flow rates, feed ratios and PET concentrations. It was found that the temperature has positive effects on H₂ selectivity and conversion, yet feed flow rate has the adverse effects. In addition, PET concentrations showed improved in H₂ selectivity in comparison to when only phenol as a solvent was involved. The Ni particles, which are the noble-based active species are more effective, thus offered good hydrogen production in the PET steam reforming process. Incorporation of La₂O₃ as support and Pd as a promoter to the Ni/Al₂O₃ catalyst significantly increased catalyst stability. The Ni–Pd/Al₂O₃–Al₂O₃ catalyst showed remarkable activity even after 36 h along with the production of carbon nanotubes, while H₂ selectivity and feed conversion was only slightly decreased.     

Boosting hydrogen production by ethanol steam reforming on cobalt-modified Ni–Al2O3 catalyst

Ethanol steam reforming (ESR) is one of the most promising reliable and recyclable technologies for hydrogen production. However, the development of robust, efficient Ni-based catalysts that minimize metal sintering and carbon deposition remains a key challenge. The influence of cobalt loading and ESR conditions on H₂ selectivity and catalytic stability is the focus of this study. Ni–Co/Al₂O₃ catalysts with various Co percentages were prepared by the co-impregnation method and complementary characterization tests were performed. Among the catalysts tested, Ni–Co/Al₂O₃ (5 wt% Co) exhibited the smallest metal crystallite size, the highest surface area, and the best catalytic performance. Thereafter, the effects of temperature, LHSV and S:C molar ratio were studied. 100% ethanol conversion and maximum H₂ selectivity (95.14%) were reached at 600 °C, 0.05 L/g_cat.h and S:C molar ratio of 12:1. Furthermore, ethanol turnover frequency (TOF) was computed for each catalyst. TOF results showed that the Ni–Co interaction had an impact on the catalytic activity. Finally, Ni2CoAl was subjected to 50-h stability test and only 6.12 mg_carbon/g_cat.h coke deposition was observed.     

Thermochemical hydrogen production using Rh/CeO2/γ-Al2O3 catalyst by steam reforming of ethanol and water splitting in a packed bed reactor

This study is focused on investigating the dual performance of Rh/CeO₂/γ-Al₂O₃ catalyst for steam reforming of ethanol (SRE) and thermochemical water splitting (TCWS) using a packed bed reactor. The catalyst is designed to be thermally stable containing an active phase of Rh and the redox component of CeO₂ for oxygen exchange, supported on γ-Al₂O₃. The catalyst has been characterised by SEM, XRD, BET, TPR, TPD, XPS and TGA before testing in the reactor. The optimal temperature for SRE reaction over this catalyst is between 700 °C and 800 °C to produce high concentrations of hydrogen (~60%), and low CO and CH₄. The selectivity towards CO and CH₄ is higher at low temperatures and drops with rise in reaction temperature. Further, Rh/CeO₂/γ-Al₂O₃ is found to be active for TCWS at relatively low temperatures (≤1200 °C). At temperatures as low as 800 °C, this catalyst is especially found suitable for multiple redox cycles, producing a total of 48.9 mmol/g_cat in four redox cycles. The catalyst can be employed for large number of redox cycles when the reactor is operated at lower temperatures. Finally, the reaction pathways have been proposed for both SRE and TCWS on Rh/CeO₂/γ-Al₂O₃ catalyst.     

Robust Mesh-type structured CuFeMg/γ-Al2O3/Al catalyst for methanol steam reforming in microreactors

Utilizing a compact, efficient and fast-response reactor for on-site reforming of liquid methanol is an effective method to solve the storage and transportation problems of hydrogen. In this paper, a mesh-type structured CuFeMg/γ-Al₂O₃/Al catalyst with strong bonding force was prepared by anodic oxidation method, and its intrinsic catalytic activity, hydrogen production capacity and start-up performance were compared with commercial granular catalyst in a plate microreactor. The results showed that although the mesh-type structured catalyst displayed lower intrinsic activity, it exhibited higher methanol conversion, which was because of the enhanced mass transfer ability. Overall, for the mesh-type structured catalyst, 27.1% higher hydrogen production capacity per unit volume was achieved when methanol conversion was 90%, and the reactor start-up time was reduced by 16.1% owing to the high thermal conductivity of the aluminum substrate. Moreover, the mesh-type structured catalyst also showed excellent stability in 160 h test.     

Opposite effects of self-growth amorphous carbon and carbon nanotubes on the reforming of toluene with Ni/α-Al2O3 for hydrogen production

Ni-based catalysts are prone to be deactivated by carbon deposition. This study aims to investigate the influence mechanism of different types of carbon deposition on the activity of Ni/α-Al₂O₃ catalyst at various steam-to-carbon (S/C) ratios during steam reforming of toluene for hydrogen production. At a low S/C ratio of 1, the catalytic activity of Ni/α-Al₂O₃ was inhibited due to the covering and blocking of Ni active sites by the formation of amorphous carbon on the Ni surface. While at a high S/C ratio of 3, more than 80 wt% of carbon deposition was found to be self-growth carbon nanotubes (CNTs) with an average diameter of around 15 nm. The activity of Ni/α-Al₂O₃ in steam reforming of toluene was unusually promoted, which can be attributed to the tip-growth mechanism of CNTs, whereby the Ni particles migrated to the tip or the surface of CNTs, resulting in the improved active site dispersion.     

Catalytic performance of Samarium-modified Ni catalysts over Al2O3–CaO support for dry reforming of methane

Mesoporous calcina-modified alumina (Al₂O₃–CaO) support was produced through the simple and economical co-precipitation method, then nickel (Ni, 10 wt%) and samarium (Sm, 3 wt%) ions loaded by two-solvent impregnation and one-pot strategies. The unpromoted/samarium-promoted catalysts were evaluated using X-ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HR-TEM), nitrogen adsorption-desorption, Temperature Programmed Oxidation/Reduction (TPR/TPO), and Field Emission Electron Scanning Microscopy (FE-SEM) methods, then investigated in methane dry reforming. The results revealed that with adding samarium to Ni catalyst through impregnation method, the average Ni crystallite size and specific surface area decreased from 11.5 to 5.75 nm and from 76.08 to 30.9 m²/g, respectively; as a result, the catalytic activity increased from about 50% to 68% at 700 °C. Furthermore, the TPO and FE-SEM tests indicated the formation of carbon with nanotube nature on the catalyst surface.     

Tri-metallic Ni–Co modified reducible TiO2 nanocomposite for boosting H2 production through steam reforming of phenol

Well-designed Co₃O₄ nanocubes (NCs) dispersed NiO/TiO₂ to construct tri-metallic reducible NiO/TiO₂/Co₃O₄ NCs structured catalyst for steam-reforming of phenol (SRP) with enhanced hydrogen production has been investigated. The controlled morphology with good dispersion was obtained, enabling efficient SRP toward selective H₂ production. Using 10% NiO- 5% Co₃O₄ NCs/TiO₂ composite, H₂ yield of 69.91% and phenol conversion of 78.4% was achieved, significantly higher than using NiO/TiO₂ and TiO₂ samples. The cubical structured Co₃O₄ dispersed NiO/TiO₂ composite showed significantly improved H₂ yield and phenol conversion due to strong metal-support interaction with reducible support for providing more active sites. The H₂ production was further increased by increasing reaction temperature, phenol concentration, feed flow rate and catalysts loading, however, they have adverse effect on the selectivity due to more CO formation. The composite catalyst possesses excellent activity and stability due to strong tri-metallic interaction and exceptional electronic interfaces. The spent catalyst analysis confirms the formation of graphene and carbon nanotubes over the reducible support. This study reveals that Co₃O₄ NCs are able to increase NiO/TiO₂ activity for H₂ production by inhibiting carbon monoxide formation and would be beneficial in other reforming applications.     

Influence of metal-support interactions on reaction pathways over Ni/CeZrOx–Al2O3 catalysts for ethanol steam reforming

This work investigates selective Ni locations over Ni/CeZrO_x–Al₂O₃ catalysts at different Ni loading contents and their influences on reaction pathways in ethanol steam reforming (ESR). Depending on the Ni loading contents, the added Ni selectively interacts with CeZrO_x–Al₂O₃, resulting in the stepwise locations of Ni over CeZrO_x–Al₂O₃. This behavior induces a remarkable difference in hydrogen production and coke formation in ESR. The selective interaction between Ni and CeZrO_x for 10-wt.% Ni generates more oxygen vacancies in the CeZrO_x lattice. The Ni sites near the oxygen vacancies enhance reforming via steam activation, resulting in the highest hydrogen production rate of 1863.0 μmol/g_cat·min. In contrast, for 15 and 20-wt.% Ni, excessive Ni is additionally deposited on Al₂O₃ after the saturation of Ni–CeZrO_x interactions. These Ni sites on Al₂O₃ accelerate coking from the ethylene produced on the acidic sites, resulting in a high coke amount of 19.1 mg_c/g_cat·h (20Ni/CZ-Al).     

Ca–Al layered double hydroxides-derived Ni-based catalysts for hydrogen production via auto-thermal reforming of acetic acid

Biomass-derived acetic acid (HAc) is an alternative resource for hydrogen production, and heat self-sustained auto-thermal reforming (ATR) of HAc shows potential for practical application, while robust and stable catalysts remain as a key factor. Ca–Al layered double hydroxides (LDHs)-derived Ni-based catalysts were synthesized by co-precipitation, and tested in ATR of HAc for hydrogen production. Over the LDHs-derived Ca_2.55Ni_0.45AlO_4.5 catalyst, active sites of Ni–CaO–Ca₁₂Al₁₄O₃₃ were formed, and interaction among Ni, CaO and Ca₁₂Al₁₄O₃₃ was proved to be a pivotal role for 1) thermal stability, 2) resistance to oxidation of Ni⁰ species, and 3) inhibiting coke deposition through catalytic cycle, CaO + CO₂↔CaCO₃ and CaCO₃+*C↔CaO+2CO, for gasification of coking precursors. Hence, the Ca_2.55Ni_0.45AlO_4.5 catalyst showed enhanced activity with no obvious deactivation in ATR: the acetic acid conversion rate was 100%, and the hydrogen yield remained stable near 2.75 mol-H₂/mol-HAc at a rate of 40.34 mmol-H₂/s/g-catalyst.     

Performance characteristics of Mo–Ni/Al2O3 catalysts in LPG oxidative steam reforming for hydrogen production

A 1:1 propane–butane mixture was used to study the effect of promoting 15 wt.% Ni/Al₂O₃ (15Ni) catalyst with small amounts of Mo (0.05, 0.1, 0.3, and 0.5 wt.%) for H₂ production during LPG oxidative steam reforming. Stability tests at 450 °C showed that lower Mo loadings (0.1 and 0.05 wt.%) had higher conversions and H₂ production rates than the non-promoted catalyst and a stable performance for the whole 18-h test period. TPO results showed that slightly more Ni sites were available for whisker formation over the Mo catalyst with 0.1 wt.% loading, the types of carbon resulting from cracking were the same on both promoted and non-promoted catalysts. Higher Mo loaded catalysts (0.3 and 0.5 wt.%) showed higher H₂ yields than the non-promoted catalysts, but lower feed-fuel conversions. XRD revealed that the loss in activity was due to oxidation of active Ni species to inactive Ni and Ni–Mo.     

A monolith CuNiFe/γ-Al2O3/Al catalyst for steam reforming of dimethyl ether and applied in a microreactor

Structured CuNi/γ-Al₂O₃/Al catalyst exhibited a good stability in steam reforming of dimethyl ether (DME SR) system, but there was a high CO concentration in outlet gas (about 25%). For the problem, a series of CuNiFe/γ-Al₂O₃/Al catalysts with different Fe content were prepared through impregnation method. It is found that the CO concentration obviously decreased after the addition of Fe. When the loading amount of Fe was 12.5 wt%, the catalyst presented the best performance: the conversion of DME reached 100% and the H₂ yield was over 0.9 in both the microreactor and fixed-bed reactor. Furthermore, cross-flow channels and parallel-flow channels were built respectively by mesh-type catalyst and plate-type catalyst in the microreactor. The gas/solid mass transfer limitations in both flow channels were investigated by Damköhler number (Da). The results showed that the Da values of cross flow were always <0.01, while the values of parallel flow were >0.01. It indicated that the diffusion over mesh-type catalyst was less influenced by temperature and reactor height, making it a more appropriate choice for the microreactor.