Efficient hydrogen production by low-temperature steam reforming of propane using catalysts with very small amounts of Pt loaded on NiMn2O4 particles

The purpose of the present work is to unveil the effect of very small amounts of Pt loaded onto a NiMn₂O₄ spinel catalyst on the chemical characteristics and catalytic activity for low-temperature steam reforming (LTSR) of propane. In the H₂-TPR curves of the Pt-loaded catalysts, the reduction corresponding to Pt²⁺ → Pt⁰ occurred largely at approximately 200–350 °C. It is due to the high accumulation of hydrogen on the PtNi alloy. X-ray photoelectron spectroscopy measurements proved that the PtNi component acted as the active species. The catalysts with Pt loaded on 40NiMn₂O₄/60γ-Al₂O₃ show higher propane conversion due to the larger metal interface area created between Pt, Ni, and MnO. In particular, the 40Pt_0.025NiMn₂O₄/60γ-Al₂O₃ catalyst maintained a very low amount of carbon deposition, a stable propane conversion of 100% and a hydrogen production capacity of 60% at 450 °C, even after 100 h of LTSR.     

Hydrogen production via catalytic gasification of ethanol. A mechanism proposal over copper–nickel catalysts

Ethanol gasification using Cu–Ni–K/γ-Al₂O₃ catalysts was studied. The reaction was carried out at a low temperature (300°C) and atmospheric pressure. The influence of the diffusional effects, the residence time and the water/ethanol molar ratio in the feed on the ethanol conversion and on the product distribution was analysed. Additional experiments were performed with monometallic catalysts, such as Cu–K/γ-Al₂O₃ and Ni–K/γ-Al₂O₃ catalysts.Ethanol gasification is favoured by a diminution of the diffusional resistances, high residence time and low water to ethanol feed ratio. A probable reaction mechanism is postulated, which is consistent with the experimental results and let identify the function of each metal (copper and nickel).     

Hydrogen generation from Al-Water reaction promoted by M-B/γ-Al2O3 (M = Co,Ni) catalyst

Al-water reaction promoted by catalysts is a promising hydrogen generation technology. In this work, a high-activity M-B/γ-Al₂O₃ (M = Co, Ni) catalyst is prepared by wet chemical reduction method. It is found that M-B/γ-Al₂O₃ catalyst significantly promotes the Al-water reaction and decreases the induction time. When the molar ratio of γ-Al₂O₃ to Co-M in Co–B/γ-Al₂O₃ catalyst is 1:1, the induction time is only 0.43 h. The catalytic activity of M-B/γ-Al₂O₃ is proportional to its active area. SEM analyses show that M-B particles are dispersed on γ-Al₂O₃ surface, which reduces the agglomeration of M-B and increases the active surface of M-B/γ-Al₂O₃, leading to a high catalytic activity. A possible mechanism is proposed, which shows that the dissociation of water molecules on γ-Al₂O₃ surface and the microgalvanic interaction between M-B and Al can promote the hydration process of passive oxide film on Al particle surface, speeding up the Al-water reaction.     

Syn-gas generation in the absence of oxygen and isotopic exchange reactions over Rh & Pt/doped-ceria catalysts

Syn-gas generation in the absence of oxygen by methane decomposition offers an interesting route to decrease reactor size and cost because methane is the only reactant in the gas phase. In this work, several catalysts were studied, Rh/CeO₂, Pt/CeO₂, Rh/(Ce_0.91Gd_0.09)O_2−x, Pt/(Ce_0.91Gd_0.09)O_2−x, Rh/γ-Al₂O₃ and Pt/γ-Al₂O₃ for methane reforming in the absence of gaseous oxygen. Rhodium showed a superior catalytic activity and selectivity with respect to Pt. This catalytic behavior may be due to the strong metal-support interaction, associated with the formation of mixed metal–oxide species at the interface. The addition of Gd³⁺ to ceria lowered the required temperatures for catalyst activation with respect to the un-doped material. Conversely to oxygen ion conducting materials, which showed a high selectivity for syn-gas generation, the non-oxygen conducting catalysts did not generated carbon monoxide. These results may be correlated to their oxygen storage capacity and ionic conductivity. Since gaseous oxygen was not delivered to the reactor, it is clear that the only source of oxygen was the catalyst. During the isothermal isotopic oxygen exchange experiments over Pt/(Ce_0.91Gd_0.09)O_2−x and Pt/γ-Al₂O₃, results illustrated that oxygen in the gas phase was exchanged with the oxygen from the catalyst. Three different molecules were detected ¹⁶O–¹⁸O, ¹⁶O–¹⁶O and ¹⁸O¹⁸O. A higher amount of oxygen was exchanged over Pt/(Ce_0.91Gd_0.09)O_2−x with respect to Pt/γ-Al₂O₃. It is proposed that mainly lattice and surface oxygen were exchanged over Pt/(Ce_0.91Gd_0.09)O_2–x and Pt/γ-Al₂O₃, respectively. It is also suggested that two types of reaction mechanisms take place, the simple and multiple hetero-exchange with the participation of one and two catalyst oxygen atoms, respectively. Similarly to methane reforming, lower temperatures were required for the oxygen exchange experiments over Rh than over Pt, as illustrated by results of the temperature-programmed exchange reactions. In summary, the properties of doped ceria may open new catalytic routes for oxidation reactions without gaseous oxygen because post-oxidation can restore its oxygen storage capacity.     

Room temperature hydrogen generation from aqueous ammonia-borane using noble metal nano-clusters as highly active catalysts

Nano-clusters of noble metals Ru, Rh, Pd, Pt and Au have been supported on γ-Al₂O₃, C and SiO₂, of which the catalytic activities have been investigated for hydrolysis of NH₃BH₃. Among these catalysts, the Ru, Rh and Pt catalysts exhibit high activities to generate stoichiometric amount of hydrogen with fast kinetics, whereas the Pd and Au catalysts are less active. Support effect has been studied by testing the hydrogen generation reaction in the presence of Pt supported on γ-Al₂O₃, VULCAN^® carbon and SiO₂, and it is found that Pt on γ-Al₂O₃, which has the smallest particle size, is the most active. Concentration dependence of the hydrogen generation from aqueous NH₃BH₃ solutions has been investigated in the presence of Pt/γ-Al₂O₃ by keeping the amount of Pt/γ-Al₂O₃ catalyst unchanged, which exhibits that the hydrogen release versus time (ml H₂ min⁻¹) does not significantly change with increasing the NH₃BH₃ concentration, indicating that the hydrogen release rate is not dependent on the NH₃BH₃ concentration and the high activity of the Pt catalyst can be kept at high NH₃BH₃ concentrations. Activation energies have been measured to be 23, 21 and 21 kJ mol⁻¹ for Ru/γ-Al₂O₃, Rh/γ-Al₂O₃ and Pt/γ-Al₂O₃ catalysts, respectively, which may correspond to the step of B–N bond breaking on the metal surfaces. The particle sizes, surface morphology and surface areas of the catalysts have been obtained by TEM and BET experiments.     

nPt (Hx−2nMoO3) as a promising catalyst for the oxidation of methanol. Synthesis and electrocatalytic properties

A new method for the synthesis of the catalyst systems Pt–Mo was suggested. nPt⁰(H_x−2nMoO₃)/GC electrodes were prepared by a redox reaction between the hydrogen-containing molybdenum bronzes and potassium tetrachloroplatinate (II) in acid solutions at open circuit potential. The electrodes were characterized by CVA, SEM, X-ray microanalysis, XRD, XPS and ICP-AES. Pt⁰conglomerates formation with nonuniform distribution over the molybdenum bronzes surface has been revealed. nPt⁰(H_x−2nMoO₃)/GC electrodes showed high catalytic activity (not inferior to Pt–Ru-catalyst) in the oxidation of carbon monoxide and methanol as compared with Pt/GC-electrodes. Catalytic effect is apparently achieved by effective oxidation of strongly chemisorbed species (CO_ads, HCO_ads), which occurs at boundaries platinum – molybdenum oxide. Therefore nPt⁰(H_x−2nMoO₃) can be considered as one of perspective catalysts for DMFC.     

Boosting alcohol electro-oxidation reaction with bimetallic PtRu nanoalloys supported on robust Ti0.7W0.3O2 nanomaterial in direct liquid fuel cells

In this work, an anatase Ti_0.7W_0.3O₂-supported Pt₃Ru nanoparticles (NPs) were fabricated by combining the advantages of the non-carbon Ti_0.7W_0.3O₂ nanosupport and the synergistic effect of the bimetallic Pt₃Ru nanoalloy that was investigated as electrocatalyst toward alcohol electrochemical oxidation. The bimetallic Pt₃Ru nanoparticles with ~3 nm in diameter were relatively well-dispersed on the surface of the anatase Ti_0.7W_0.3O₂ nanosupport via a surfactant-free microwave-assisted polyol route that, which was attributable to the good dispersibility of ethylene glycol and the rapid, uniformity of the microwave heating. For methanol and ethanol electrochemical oxidation, the as-obtained Pt₃Ru (NPs)/Ti_0.7W_0.3O₂ electrocatalyst exhibited the low onset potential (~0.10 V vs. NHE for MOR and ~0.35 V vs. NHE for EOR) and high mass activity (~350.84 mA mg_Pt^?1 for MOR and ~274.59 mA mg_Pt^?1 for EOR) compared to the commercial Pt (NPs)/C (E-TEK) electrocatalyst. Additionally, the CO-stripping and CA results indicated the remarkably enhanced CO-tolerance of the Pt₃Ru (NPs)/Ti_0.7W_0.3O₂ catalyst. After the 5000-cycle accelerated durability test (ADT) in acidic ethanol media, the bimetallic Pt₃Ru (NPs)/Ti_0.7W_0.3O₂ catalyst only showed the mass activity loss of 19.11% of its initial mass activity, compared with the severe deterioration of 44.04% of the commercial Pt (NPs)/C (E-TEK) catalyst. The outstanding results could be interpreted due to the bifunctional mechanism of the Pt₃Ru nanoalloys combining with the synergistic effect between the bimetallic nanoalloy and the mesoporous Ti_0.7W_0.3O₂ nanosupport as well as the superior anti-corrosion of the TiO₂-based nanosupport under acidic and oxidative environments.     

Cu supported on ZnAl-LDHs precursor prepared by in-situ synthesis method on γ-Al2O3 as catalytic material with high catalytic activity for methanol steam reforming

A novel catalyst precursor ZnAl-LDHs/γ-Al₂O₃ was prepared by in-situ synthesis method, and the copper was supported on calcined hydrotalcite catalyst precursor by wet impregnation. The correlation between the structure and the catalytic activity for methanol steam reforming was studied by XRD, SEM, TPR, chemisorption N₂O, IR and N₂ adsorption techniques. The results showed that the ZnAl-LDHs was successfully synthesized by in-situ synthesis method on γ-Al₂O₃ and the copper mass fraction had a great effect on the interactions between support and copper species. Furthermore, the catalyst reducibility and copper surface area evidently influenced catalytic activity for methanol steam reforming. The 10% Cu/γ-Al@MMO exhibited the best catalytic activity, that was, the methanol conversion was 99.98% and the CO concentration was only 0.92% at 300 °C in hydrogen production by methanol steam reforming.     

Catalytic steam reforming of biomass-derived acetic acid over modified Ni/γ-Al2O3 for sustainable hydrogen production

In order to obtain sustainable H₂, the catalytic steam reforming of acetic acid derived from biomass was performed by using the catalysts modified with basic promoters (Mg, La, Cu, and K). La and K increased the total basicity of Ni/γ-Al₂O₃ by 30.6% and 93.4%, respectively, which could induce ketonization, producing acetone. In contrast, Mg reduced the number of middle and strong basic sites by 17.2% and improved the number of weak basic sites by 5% for Ni/γ-Al₂O₃, which promoted the steam reforming of acetic acid (ca. 100% of H₂ and carbon selectivity at even 450 °C) without ketonization. Moreover, the amount of carbon deposited on Ni/Mg/γ-Al₂O₃ was 55.1% less than that deposited on Ni/γ-Al₂O₃. When Cu was employed, the conversion was ca. 60% with less than 70% of H₂ selectivity, at all temperatures considered herein.     

Hydrogen production by methane decomposition: A comparative study of supported and bulk ex-hydrotalcite mixed oxide catalysts with Ni,Mg and Al

A catalytic comparative study of CO_x-free hydrogen production by methane decomposition was carried out. Catalytic performances of bulk Ni-mixed oxides derived from Ni/Mg/Al-hydrotalcites (ex-HTs-Ni) were compared with those obtained with Ni supported on mixed oxides derived from Mg/Al-hydrotalcites (Ni/ex-HTs), or on commercial supports (γ-Al₂O₃, MgO and MgO-modified γ-Al₂O₃). Catalyst characterization and their catalytic performance showed both ex-HTs-Ni and Ni/ex-HTs appear to be a similar regardless of their method of preparation. Ni/γ-Al₂O₃ was the best supported catalyst, although the catalytic performances of the ex-HTs catalysts were better. Higher NiMg interaction in ex-HTs provides higher resistance to deactivation. Characterization by TG, Raman spectroscopy and TEM of spent catalysts in the reaction suggest the degree of ordering of the graphitic layers of the carbon deposit onto the catalyst surface is the key factor in the catalyst deactivation. The higher degree of ordering or graphitization of the carbon produced with the higher concentration of sp2 carbons on the surface of the Ni/γ-Al₂O₃ favours its faster deactivation by Ni-coverage than the bulk catalyst (ex-HT-Ni), in which the MWNT type carbon is mainly obtained.     

Effect and behavior of cerium oxide in Ni/γ-Al2O3 catalysts on autothermal reforming of methane: CeAlO3 formation and its role on activity

Nickel supported γ-alumina (Ni/γ-Al₂O₃) catalysts are well-known to be highly active on the autothermal reforming of methane, but to be unstable due to coke deposition. Cerium oxide (CeO₂) is one of promising promoter to overcome the fast deactivation of nickel-based catalysts by coke formation. Herein, catalytic behavior of CeO₂ over Ni/γ-Al₂O₃ catalysts on the autothermal reforming of methane was investigated. The catalytic activity was maintained for 100 h with H₂/CO molar ratio of 1.9. The formation of CeAlO₃ is observed at the reduction and reaction conditions. In this work, it was found that the formation of CeAlO₃ promoted the catalytic oxidation toward CO₂ and prevented the formation of α-Al₂O₃ and nickel-aluminate, resulting in stable activity for autothermal reforming of methane.     

Highly dispersed mesoporous Cu/γ-Al2O3 catalyst for RWGS reaction

The extensive use of fossil energy leads to the wanton emission of CO₂ and serious environmental problems. The resource utilization of CO₂ is an effective way to solve this problem. The key of CO₂ resource utilization is the design and preparation of high active CO₂ hydrogenation catalyst. In this paper, supported Cu/γ-Al₂O₃ catalysts were prepared by wet impregnation and grinding methods, respectively. The physicochemical properties of the prepared Cu/γ-Al₂O₃ catalysts were characterized by XRD, BET, CO₂-TPD and Quasi in-situ XPS, and the reducibility of the precursors was studied by H₂-TPR. The results show that Cu content directly affects the Cu⁰ species crystallinity and even affects the adsorption and activation of CO₂ molecules for the Cu/γ-Al₂O₃ catalyst. The dispersion of Cu⁰ species in the prepared Cu/γ-Al₂O₃ catalysts can be further improved by grinding method. The CO₂ reaction rate on the Cu/γ-Al₂O₃ catalyst prepared by grinding method can be significantly increased to 2.12 × 10^?5 mol/g_cat/s at 400 °C.     

Improved charge transfer and morphology on Ti-modified Cu/γ-Al2O3/Al catalyst enhance the activity for methanol steam reforming

The metal-oxide interaction has been considered as an effective factor for catalytic performance in methanol steam reforming. In this work, Ti modified Cu/γ-Al₂O₃/Al catalyst was prepared by anodization technology. It is found that the addition of Ti can largely increase the surface area of the carrier and thus improve the dispersion of copper. The co-existence of Ti⁴⁺ and Ti³⁺ makes the charge transfer between Cu and Ti easier, which improves the redox performance of copper. The DFT calculations reveal that Ti also enhance the adsorption capacity of water and methanol on the surface of the catalysts. Besides, Ti also reduce the acid density on the carrier, inhibit methanol dehydration reaction and thereby reduce the selectivity of the DME. The optimal catalyst CuTi_1.9/γ-Al₂O₃/Al achieves nearly 100% conversion at 275 °C, while the methanol conversion of Cu/γ-Al₂O₃/Al is 82%. And the H₂ output of CuTi_1.9/γ-Al₂O₃/Al reached 69.17 mol/(kg_cat·h) at 300 °C.     

Conversion of sugarcane bagasse to gaseous and liquid fuels in near-critical water media using K2O promoted Cu/γ-Al2O3–MgO nanocatalysts

Bagasse conversion to H₂, CO and light gaseous hydrocarbons as gaseous fuels, and higher alcohols and ethers as liquid fuels and fuel additives were performed in a basic water medium with near-critical condition in presence of potassium promoted Cu/γ-Al₂O₃–MgO catalysts. The catalysts were extensively characterized using ICP, XRD, TPR, BET, CO chemisorption and TEM techniques. In order to investigate support stability at reaction condition, XRD test also was carried out for used catalysts. Maximum dispersion of 48% and minimum average particles sizes of 8.4 nm were obtained for Cu20–K7.5/γ-Al₂O₃–MgO catalyst. Copper and potassium effects on quality and quantity of gaseous and liquid products were investigated. The maximum amounts of H₂ (10 mmol g⁻¹ of bagasse) and total produced gases (41 mmol g⁻¹ of bagasse) were obtained with unpromoted Cu20/γ-Al₂O₃–MgO catalyst. Addition of K increased the bagasse conversion to liquid fuels. Potassium made the process more selective for alcohols and ethers production. Maximum amount of alcohols and ethers (83.3 mmol g⁻¹ of bagasse) was obtained for Cu20–K7.5/γ-Al₂O₃–MgO catalyst.     

Highly effective hydrogen isotope separation by cryogenic gas chromatography in a new stationary phase material MnCl2@CPL-1@γ-Al2O3

In this work, metal-organic framework compound CPL-1 of a formula {[Cu₂(pzdc)₂(pyz)]?2H₂O}_n (pzdc = pyrazine-2,3-dicarboxylate, pyz = pyrazine) possessing kinetic quantum sieving effect on H₂/D₂ separation was selected to prepare two new chromatography stationary phase materials CPL-1@γ-Al₂O₃ and MnCl₂@CPL-1@γ-Al₂O₃ by loading CPL-1 on γ-Al₂O₃ particles with size 80–100 mesh through repeating in situ crystallization process, and afterwards by loading MnCl₂ on CPL-1@γ-Al₂O₃ via impregnation approach. The two optimized materials were thoroughly characterized by IR, XRD, SEM, EDS and TG/DTA method. The experimental results showed that, under liquid nitrogen temperature by using just 1-m chromatographic column and cheap He gas as carrier gas, the MnCl₂@CPL-1@γ-Al₂O₃ can solve the problem of long separation time and trailing phenomenon existing in the CPL-1@γ-Al₂O₃ column, can realize highly effective hydrogen isotope H₂/D₂ separation with good separation resolution (R = 1.62) and approximate Gauss distribution of chromatographic peak, can be used for both qualitative and quantitative analysis of hydrogen isotope H₂/D₂ with short separation time of 6.5 min.     

Promoted catalytic behavior over γ-Al2O3 composited with ZSM-5 for crude methanol conversion to dimethyl ether

γ-Al₂O₃ was composited with ZSM-5 molecular sieve to improve its catalytic performance and hydrothermal stability during the conversion of crude methanol into dimethyl ether (DME). When prepared by a liquid-phase coating chemical compounding, the ZSM-5/γ-Al₂O₃ composite catalyst reached an excellent methanol conversion of 91.9% and DME selectivity of 100%. The DME yield was increased by about 13% compared to only using γ-Al₂O₃. Partial desiliconization and dealumination of the ZSM-5 molecular sieve effectively reduced the surface acid center strength and increased the mesoporous ratio. The special composite phase interface effectively decreased surface charge density of γ-Al₂O₃ and formed the B (Brønsted) - L (Lewis) synergistic active centers. All these factors contribute to improving the catalytic performance, hydrothermal stability and resistance to deactivation of ZSM-5/γ-Al₂O₃ during the conversion of crude methanol to DME.     

Effect of heat recirculation on the self-sustained catalytic combustion of propane/air mixtures in a quartz reactor

The self-sustained catalytic combustion of propane is experimentally studied in a two-pass, quartz heat-recirculation reactor (HRR) and compared to that in a no (heat) recirculation reactor (NRR). Structured monolithic reactors with Pt/γ-Al₂O₃, LaMnO₃/γ-Al₂O₃, and Pt doped perovskite catalysts have been compared in the HRR and NRR configurations. Heat recirculation enhances combustion stability, by widening the operating window of self-sustained operation, and changes the mode of stability loss from blowout to extinction. It is found that thermal shields (upstream and downstream of the monolith) play no role in the stability of a HRR but increase the stability of a NRR. The stability of a HRR follows this trend: Pt/γ-Al₂O₃ > doped perovskite > LaMnO₃/γ-Al₂O₃. Finally, a higher cell density monolith enlarges the operating window of self-sustained combustion, and allows further increase of the power density of the process.     

CO2 reforming of methane on Ni/γ-Al2O3 catalyst prepared by dielectric barrier discharge hydrogen plasma

Ni/γ-Al₂O₃ catalyst was prepared by direct treatment of Ni(NO₃)₂/γ-Al₂O₃ precursor with dielectric barrier discharge (DBD) hydrogen plasma at different input powers, characterized by XRD, H₂-TPR, CO₂-TPD, N₂ adsorption and TEM, respectively, and used as the catalyst for CO₂ reforming of methane (CRM). The results showed that the input power obviously affected the reduction degree and catalytic performances of catalysts. Low input power under 40 W mainly resulted in the decomposition of nickel nitrate into Ni oxides. The reduction degree, catalytic activity and stability increase with the input power. Similar catalytic performances in CRM reaction can be obtained when the power exceeds 80 W. Compared with the Ni/Al₂O₃ catalyst prepared by traditional method, Ni/γ-Al₂O₃ samples prepared by H₂ DBD plasma exhibit better activities, stability and anti-carbon deposit performances. It is mainly ascribed to smaller Ni particle size, more basic sites and weaker basicity. The increase of Ni particle sizes due to the sintering at high temperature results in the decrease of catalytic activities and coke formation.     

Understanding the role of K on PtCo/Al2O3 for preferential oxidation of CO in H2

CO preferential oxidation reaction (CO-PROX) can effectively eliminate CO in H₂ rich atmosphere to avoid CO poison the Pt anode of Proton Exchange Membrane Fuel Cell (PEMFC). To match the operation temperature window for PEMFC, PtCo nanoparticles supported on K modified Al₂O₃ (PtCo/K–Al₂O₃) were prepared to promote CO-PROX activity. The addition of K species weakened the interaction between PtCo nanoparticle and support, which improved the dispersion of Pt particles and redox property of PtCo/Al₂O₃. It also facilitated the formation of Pt₃Co species and active surface ?OH groups, which were involved in CO-PROX reaction. According to in situ DRIFTS spectra, HCO₃^? and HCOO^? were intermediates of PtCo/K–Al₂O₃ catalyzed CO-PROX at low temperature and high temperature, respectively. Thus, the addition of 1 wt% K to PtCo/Al₂O₃ (PtCo/1K–Al₂O₃) could completely oxidize CO in the temperature range of 127–230 °C with O₂ selectivity at 50%. The 100% CO conversion temperature window of PtCo/1K–Al₂O₃ is expanded by 100 °C in comparison of PtCo/Al₂O₃.