Alicia Carrero

In this work, sustainable hydrogen production from green methanol via oxidative reforming was investigated over agglomerated Co-Cr/SBA-15 catalysts. A mixed factorial design of experiments was applied to the effects of temperature, weight hourly space velocity (WHSV), steam-to-carbon ratio (S/C), and oxygen-to-carbon ratio (O₂/C) on methanol conversion and hydrogen yield. The developed models exhibited good predictive performance within the investigated operating domain. Temperature and WHSV were identified as the most influential variables for both responses, whereas increasing the S/C ratio significantly enhanced hydrogen yield. In contrast, higher O₂/C ratios promoted methanol conversion, but reduced hydrogen yield due to enhanced oxidation pathways. Optimal conditions for hydrogen production were identified at 600 °C, WHSV= 30 h⁻¹, S/C = 2, and O₂/C = 0.10. Under these conditions, the agglomerated catalyst showed catalytic performance comparable to that of the powdered counterpart, confirming that shaping with bentonite does not compromise activity. Furthermore, the shaped catalyst retained approximately 95% of its initial methanol conversion after 50 h time-on-stream while maintaining an almost constant hydrogen yield, with negligible coke formation and cobalt sintering. These results demonstrate the potential of agglomerated Co-Cr/SBA-15 catalysts for hydrogen production from green methanol under the investigated oxidative steam reforming conditions and stable performance over 50 h time-on-stream.

This study investigates the oxidative steam reforming (OSR) of simulated bio-oil aqueous fractions using Co/CeO₂-SBA-15 catalysts. Five representative compounds—methanol, acetic acid, hydroxyacetone, phenol, and furfural—were evaluated to assess their reactivity for hydrogen production. Aliphatic compounds achieved nearly complete conversion and stable hydrogen yields, while aromatic structures led to lower conversion and higher coke formation. Furfural exhibited higher reactivity than phenol due to its furan ring and aldehyde group. Catalysts with 10 and 20 wt.% Ce showed similar activity, but Co/20CeO₂-SBA-15 presented lower hydrogen yield. For this reason, next experiments of OSR of model compound mixtures were carried out only with Co/10CeO₂-SBA-15. To approach real bio-oil complexity, ternary and quinary mixtures were tested. High conversion and hydrogen yield were maintained over 50 h when the ternary mixture (methanol, hydroxyacetone, and acetic acid) was fed. When the quinary mixture was used as feedstock, which includes furfural and phenol, lower conversions were obtained for these compounds compared to aliphatic ones, although conversions remained above 80% after 50 h (88.9% for furfural and 82.6% for phenol). These results highlight Co/10CeO₂-SBA-15 as a viable catalyst for bio-oil aqueous fraction valorization under OSR conditions.

This work explores the effect of the incorporation of CeO₂ into Co/SBA-15 catalysts in hydrogen production through acetic acid oxidative steam reforming as a bio-oil aqueous phase model compound. CeO₂ was incorporated (5–30 wt.%) to improve the physicochemical properties of the catalyst. XRD analysis confirmed that the addition of CeO₂ resulted in smaller Co⁰ mean crystallite sizes, while H₂-TPR showed enhanced reducibility properties. The catalytic performance was evaluated in the 400–700 °C range, S/C molar ratio = 2, O₂/C molar ratio = 0.0375, WHSV = 30.2 h⁻¹, and P = 1 atm. Catalysts containing 10 and 20 wt.% of CeO₂ exhibited the best catalytic performance, achieving nearly complete conversions and H₂ yield values, approaching thermodynamic equilibrium at 550 °C. Both samples maintained an acetic acid conversion above 90% after 30 h of time-on-stream, with H₂ yields above 55% along the steam reforming tests. This agrees with their lower coke formation rates (7.2 and 12.0 mg_coke·g_cat⁻¹·h⁻¹ for Co/10CeO₂-SBA15 and Co/20CeO₂-SBA15, respectively).

This work examines the influence of metal loading and the Ni/Cr ratio of Ni-Cr/SBA-15 catalysts on bioethanol steam reforming for the first time. The characterization of the synthesized samples reveals that higher Cr amounts result in lower Ni crystallite sizes due to the promoting effect of Cr, thereby enhancing the dispersion of the active phase. The catalytic performance has been evaluated in terms of ethanol conversion and H₂ TOF (min⁻¹). Ethanol conversion exhibits an increasing trend with higher Ni content, reaching up to 90% for samples containing 15 wt.%. By increasing the Cr content (lower Ni/Cr ratio) the results evidence a similar trend. A synergistic effect between Ni and Cr was appreciated in conversion values when the Ni content was below 11 wt.% and the Cr content exceeded 2 wt.%, which coincides with a smaller Ni crystallite size. Concerning the H₂ TOF, the catalyst with the lowest Ni content (7 wt.%) exhibited a higher value with a notable enhancement upon increasing the Cr loading. However, a considerable decrease in H₂ TOF was observed for samples with higher Ni loading. Therefore, the best catalytic performance, achieving nearly complete ethanol conversion and high hydrogen production, was reached when using catalysts with 7 wt.% Ni; the Cr loading should be increased to around 2 wt.%.

Mesoporous materials with high surface area, large pore volume, and adjustable pore size are promising in the fields of adsorption and heterogeneous catalysis. In this work, ordered mesoporous ceria structures were successfully prepared via nanocasting using SBA-15 as a template, with Ce(NO₃)₃·6H₂O or CeCl₃·7H₂O as ceria precursors. The materials were characterized before and after template removal. The CeO₂ crystallite size in the CeO₂/SBA-15 composites increases with successive impregnations until it reaches the pore size of the SBA-15. Upon removal of the SBA-15 template, the synthesized materials exhibit pore diameters corresponding to the wall thickness of the SBA-15, evidencing that the inverted structure was obtained. Mesoporous ceria exhibits increasingly ordered structure up to five successive impregnations with 1.3 mmol_Ce/g_SBA-15. Using cerium chloride as a precursor, highly ordered structures were reached after only three impregnations. The feasibility of this synthesis in fewer steps (1, 3, and 5), employing the same amount of Ce precursor (6.7 mmol_Ce/g_SBA-15), was also studied. Results show a higher ordering degree and oxygen mobility capacity at higher impregnation steps. The mesostructured ceria samples exhibit significantly higher oxygen mobility than commercial bulk ceria, along with high thermal stability, which highlights the usefulness of these structures.

Oxidative steam reforming allows higher energy efficiency and lowers coke deposition compared to traditional steam reforming. In this work, CeO₂-based supports have been prepared with Ni as the active phase, and they were tested in the oxidative steam reforming of acetic acid. The influence of the O₂/AcOH molar ratio (0–0.3) has been evaluated over Ni/CeO₂. The results stated that by increasing oxygen content in the feeding mixture, acetic acid conversion increases, too, with a decrease in coke deposition and hydrogen yield. To have a proper balance between the acetic acid conversion and the hydrogen yield, an O₂/AcOH molar ratio of 0.075 was selected to study the catalytic performance of Ni catalysts over different supports: commercial CeO₂, a novel mesostructured CeO₂, and CeO₂-SBA-15. Due to higher Ni dispersion over the support, the mesostructured catalysts allowed higher acetic acid conversion and hydrogen yield compared to the nonporous Ni/CeO₂. The best catalytic performance and the lowest coke formation (120.6 mg_coke·g_cat⁻¹·h⁻¹) were obtained with the mesostructured Ni/CeO₂. This sample reached almost complete conversion (>97%) at 500 °C, maintaining the hydrogen yield over 51.5% after 5 h TOS, being close to the predicted value by the thermodynamic equilibrium that is due to the synergistic coordination between Ni and CeO₂ particles.

This work focuses on the support effect of the performances of Co based catalysts for acetic acid steam reforming. SBA-15, a well ordered hexagonal mesoporous silica structure, and CeO₂ have been selected as the supports, with the impact of chromium addition also being investigated. Better acetic acid steam reforming performances have been recorded for CeO₂ compared to SBA-15 supported catalysts and, in particular, the 7Co/CeO₂ catalyst showed the highest values of acetic acid conversions with enhanced H₂ yields below 480 °C, in comparison to the other investigated catalytic formulations. In addition, more pronounced coke depositions and acetone concentrations have been obtained with CeO₂ supported catalysts, due to the tendency of ceria to catalyse the ketonization reaction. Chromium addition to Co/SBA-15 catalysts led to an enhancement in the activity towards acetic acid steam reforming, while on CeO₂ supported catalysts no improvement in the catalysts’ activity was observed. However, on both SBA-15 and CeO₂ supported catalysts, Cr addition reduced the amount of coke deposited on the catalysts surface.