Thermo-photo synergic effect on methanol steam reforming over mesoporous Cu/TiO2–CeO2 catalysts

Methanol steam reforming (MSR) is considered as an effective method for hydrogen storage and generating high-quality hydrogen for fuel cells. In this work, mesoporous Cu/TiO₂–CeO₂ catalysts are proposed to achieve efficient MSR based on synergetic effects of thermal and photon energies. Optimal Ti/Ce molar ratio is found to be 2:1, for which excellent methanol conversion of 100% and extremely low CO selectivity of 2.2% are achieved for thermal catalysis. Further applying UV light (280–400 nm) irradiation while keeping the same temperature, the hydrogen production rate is enhanced to be 78.8 mmol/h/g from 58.6 mmol/h/g. The underlying mechanism is attributed to photogenerated electron hole pairs promoting the REDOX reaction of intermediate product methyl formate based on in situ diffuse reflectance infrared fourier transform spectra (DRIFTS). This work provides a new method to enhance methanol steam reforming performance via thermo-photo synergic effects, and paves a way for the development of direct solar driven MSR techniques.     

Production of hydrogen via methanol steam reforming over mesoporous CeO2–Cu/KIT-6 nanocatalyst: Effects of polar aprotic tetrahydrofuran solvent and ZrO2 promoter on catalytic performance

In the present study, the preparation of CeO₂–Cu/KIT-6 catalysts was made by the conventional impregnation approach using a polar protic solvent (ethanol), and a polar aprotic solvent (tetrahydrofuran (THF)) as well as ethylene glycol (EG)-assisted impregnation approach. The impact of the zirconium promoter on the catalytic activity of the catalyst was evaluated in methanol steam reforming (MSR). The characterization of the prepared catalysts was carried out by XRD, XRF, BET, FE-SEM, H₂-TPR, and TEM analyses. According to the characterization outcomes, the application of THF as an impregnation solvent and incorporation of ZrO₂ remarkably reduced the size of Cu particles and increased the dispersion of metal species. ZrO₂-promoted CeO₂–Cu/KIT-6 catalyst prepared using the THF solvent showed the most suitable catalytic activity with hydrogen selectivity of 99.8%, methanol conversion of 96%, and CO selectivity of 0.7% at 300 °C. Furthermore, the catalytic stability of the synthesized catalysts was investigated over 100 h of operation.     

CuFeO2–CeO2 nanopowder catalyst prepared by self-combustion glycine nitrate process and applied for hydrogen production from methanol steam reforming

Hydrogen (H₂) is being considered as an alternate renewable energy carrier due to the energy crisis, climate change and global warming. In the chemical industry, hydrogen production is mainly accomplished by the steam reforming of natural gas. In the present study, CuFeO₂–CeO₂ nanopowder catalyst with a heterogeneous delafossite structure was prepared by the self-combustion glycine nitrate process and used for steam reforming of methanol (SRM). The precursor solution was fabricated from Cu–Fe–Ce metal-nitrate mixed with glycine and an aqueous solution. The prepared CuFeO₂–CeO₂ nanopowder catalyst was studied by different physical and chemical characterization techniques. The prepared CuFeO₂–CeO₂ nanopowder catalyst was immensely porous with a coral-like structure. The BET surface area measurement revealed that the specific surface area of as-combusted CuFeO₂–CeO₂ nanopowder varied from 5.6248 m²/g to 19.5441 m²/g. In addition, the production rate of CuFeO₂–CeO₂ was improved by adding CeO₂ and adjusting the feeding rate of the methanol. The highest H₂ generation rate of the CuFeO₂–CeO₂ catalyst was 2582.25 (mL STP min⁻¹ g-cat⁻¹) at a flow rate of 30 sccm at 400 °C. Hence, the high specific surface area of the 70CuFeO₂–30CeO₂ nanopowder catalyst and the steam reforming process could have a very important industrial and economic impact.     

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.     

Production of hydrogen from methanol steam reforming using CuPd/ZrO2 catalysts – Influence of the catalytic surface on methanol conversion and CO selectivity

Electricity generation for mobile applications by proton exchange membrane fuel cells (PEMFCs) is typically hindered by the low volumetric energy density of hydrogen. Nevertheless, nearly pure hydrogen can be generated in-situ from methanol steam reforming (MSR), with Cu-based catalysts being the most common MSR catalysts. Cu-based catalysts display high catalytic performance, even at low temperatures (ca. 250 °C), but are easily deactivated. On the other hand, Pd-based catalysts are very stable but show poor MSR selectivity, producing high concentrations of CO as by-product. This work studies bimetallic catalysts where Cu was added as a promoter to increase MSR selectivity of Pd. Specifically, the surface composition was tuned by different sequences of Cu and Pd impregnation on a monoclinic ZrO₂ support. Both methanol conversion and MSR selectivity were higher for the catalyst with a CuPd-rich surface compared to the catalyst with a Pd-rich surface. Characterization analysis indicate that the higher MSR selectivity results from a strong interaction between the two metals when Pd is impregnated first (likely an alloy). This sequence also resulted in better metallic dispersion on the support, leading to higher methanol conversion. A H₂ production rate of 86.3 mmol h^?1 g^?1 was achieved at low temperature (220 °C) for the best performing catalyst.     

A comparative study on the performance of mesoporous SBA-15 supported Pd–Zn catalysts in partial oxidation and steam reforming of methanol for hydrogen production

Using mesoporous SBA-15 (Santa Barbara Amorphous No. 15, a mesoporous material) as support, Pd–Zn nanocatalysts with varying Pd and Zn content were tested for hydrogen production from methanol by partial oxidation and steam reforming reactions. The physico-chemical characteristics of the synthesized SBA-15 support were confirmed by XRD, N₂ adsorption, SEM and TEM analyses. The PdZn alloy formation during the reduction of Pd–Zn/SBA-15 was revealed by XRD and DRIFT study of adsorbed CO. Also, the correlation between Pd and Zn loadings and PdZn alloy formation was studied by XRD and TPR analyses. The metallic Pd surface area and total uptakes of CO and H₂ were measured by chemisorption at 35 °C. The metallic Pd surface area values are in linear proportion with the Pd loading. The formation of PdZn alloy during high temperature reduction was confirmed by a shift in absorption frequency of CO on Pd sites to lower frequency due to higher electron density at metal particles resulted from back-donation. The reduced Pd–Zn/SBA-15 catalysts were tested for partial oxidation of methanol at different temperatures and found that catalyst with 4.5 wt% Pd and 6.75 wt% Zn on SBA-15 showed better H₂ selectivity with suppressed CO formation due to the enhanced Pd dispersion as well as larger Pd metallic surface area. The O₂/CH₃OH ratio is found to play a significant role in CH₃OH conversion and H₂ selectivity. The performance of 4.5 wt% Pd–6.75 wt% Zn/SBA-15 catalyst in steam reforming of methanol was also tested. Comparatively, the H₂ selectivity is significantly higher than that in partial oxidation, even though the CH₃OH conversion is less. Finally, the long term stability of the catalyst was tested and the nature of PdZn alloy after the reactions was found to be stable as revealed from the XRD pattern of the spent catalysts.     

Preparation of mesoporous nanostructure NiO–MgO–SiO2 catalysts for syngas production via propane steam reforming

In this research, the propane steam reforming (PSR) as a promising alternative route over a mesoporous NiO–MgO–SiO₂ catalyst to produce syngas (SG) was undertaken. This catalyst was prepared using a co-precipitation method followed by hydrothermal treatment. The influence of such catalyst preparation factors as the hydrothermal time and temperature, pH and calcination temperature on the physicochemical characteristics of the prepared samples were examined. Next, these materials were characterized through the BET-BJH, XRD, TPR, and FTIR analyses. The thermal stability of this catalyst was tested through the TGA and DTA techniques. Furthermore, the deactivation of the calcined catalysts at different temperatures was investigated via the TPO analysis. The utilized synthesis method led to preparation of a species with a mesoporous structure possessing a rather high surface area of 741 m²g^-1. The catalyst performance at a reaction temperature of 550 °C revealed that, the increment in calcination temperature from 500 to 800 °C led to lowering of the propane conversion as well as the hydrogen yield from 65 to 37.4% and 39.4 to 22.6%, respectively. Meanwhile, the extent of the deposited coke upon the catalyst surface was reduced when implementing the higher calcination temperature. This was attributed to high amounts of the NiO, which was included in the solid solution containing the MgO–SiO₂ support. In other words, the isolation of Ni²⁺ with Mg²⁺ species and strong interaction between NiO and MgO decreased the NiO particle size hence, its reducibility. These in turn led to the formation of smaller active sites possessing higher deactivation resistance against sintering and coke deposition. Thus, a highly active and stable catalyst was developed.     

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.     

High-purity hydrogen production by sorption-enhanced methanol steam reforming over a combination of Cu–Zn–CeO2–ZrO2/MCM-41 catalyst and (Li–Na–K) NO3·MgO adsorbent

In this study, sorption-enhanced methanol steam reforming (SEMSR) was applied to generate high-purity hydrogen. The mesoporous MCM-41 as support and CuO, ZnO, CeO₂, ZrO₂ as active agents and promoters were employed for the catalyst preparation. In addition, (Li–Na–K) NO₃·MgO as a CO₂ adsorbent was prepared by the wet mixing method. The fresh and used catalysts were characterized by XRD, BET, FTIR, FESEM, TEM, H₂-TPR and TGA analyses. Also, the CO₂ sorbent was studied by XRD, BET, FESEM, TEM and TGA analyses before and after the reaction. The SEMSR performances of the synthesized catalyst and adsorbent were evaluated experimentally in a fixed-bed reactor. The effect of various conditions such as temperature, WHSV, feed molar ratio and sorbent/catalyst ratio were investigated. The best results were obtained at 300 °C, a feed molar ratio (water/methanol) of 2:1, a WHSV of 1.62 h^?1, and the sorbent/catalyst ratio of 8:1, which produced 99.8% hydrogen, 25% more than the hydrogen production during conventional methanol steam reforming. Moreover, the cyclic stability of the catalyst and the sorbent was studied for 10 cycles.     

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.     

Anti-sintering mesoporous Ni–Pd bimetallic catalysts for hydrogen production via dry reforming of methane

In this work, a series of mesoporous silica supported nickel or nickel-palladium catalysts were synthesized and performed in dry reforming of methane (DRM) reaction for producing syngas. Compared with the monometallic catalyst, the Ni–Pd bimetallic catalysts, especially synthesized by the OA-assisted route, exhibited promising yields of H₂ and CO in the catalytic DRM reaction, achieved at 63% and 69% over NiPd-SP-OA bimetallic catalyst at the reaction temperature of 700 °C, respectively. TEM image results confirmed that no obvious sintering phenomenon happened on spent NiPd-SP-OA bimetallic catalyst within 1550 min time-on-stream reaction. Based on the results of XRD, XPS and H₂-TPR, it could be known that the superior catalytic performance on NiPd-SP-OA catalyst were main ascribed to the smaller-sized Ni nanoparticles with a uniform metal dispersion and a larger fraction of exposed active sites (Ni⁰).     

Hydrogen production from oxidative steam reforming of ethanol over rhodium catalysts supported on Ce–La solid solution

The catalytic behaviors of Rh catalysts supported on Ce–La solid solution in H₂ production from the oxidative steam reforming (OSR) of ethanol were studied for the first time. 1%Rh/Ce_0.7La_0.3O_y exhibits 100% ethanol conversion at 573 K with H₂ yield rate 214 μmol g-cat⁻¹ s⁻¹, which is 150 K lower than that required for comparable performance with 1%Rh/CeO₂. La doping also enhanced the stability by accelerating CH₃COCH₃ conversion and gave low CO selectivity due to the high water gas shift activity. X-ray diffraction and Raman spectroscopy characterizations indicate the formation of Ce–La solid solutions and oxygen vacancies. H₂ temperature-programmed reduction and thermo-gravimetric measurement results confirmed that the redox properties of Rh/CeO₂ were greatly enhanced by La doping, which accelerated ethanol conversion, promoted H₂ yield, and maintained good long–term activity for the OSR reaction.     

Hydrogen production from oxidative steam reforming of ethanol over Ir catalysts supported on Ce–La solid solution

The Ce_1?xLa_xO_2?δ solid solution (CL) supported Ir (nIr/CL, n = 2, 5 and 10 wt.%) catalysts are studied for H₂ production from ethanol oxidative steam reforming (OSR). The Ir dispersion, surface area, oxygen vacancy density and carbon deposition resistance of nIr/CL catalysts are greatly enhanced compared with Ir/CeO₂. Among the tested catalysts, 5%Ir/CL shows the best catalytic performance, exhibiting >99.9% ethanol conversion at 400 °C with H₂ yield rate of 323 μmol·g_cata^?1·s^?1 and no obvious carbon deposition after used. The 5%Ir/CL catalyst contains the highest amount of reducible interface Ce⁴⁺, leading to a strong interaction with surface Ir species at the metal-support interface during the OSR reaction. The strong interaction induces Ir to be well dispersed on the CL support, and is associated with more redox-active sites (interface Ce⁴⁺/Ce³⁺), to guarantee high activity.     

Role of CeO2/ZrO2 mole ratio and nickel loading for steam reforming of n-butanol using Ni–CeO2–ZrO2–SiO2 composite catalysts: A reaction mechanism

This study presents steam reforming of n-butanol to synthesis gas using high surface area mesoporous Ni–CeO₂–ZrO₂–SiO₂ composite catalysts. The reaction proceeds through a combination of dehydrogenation, dehydration, and cracking reactions with propanal, butanal, and C₂–C₄ hydrocarbons as intermediate compounds. The ceria forms a solid solution with zirconia, promotes dispersion of nickel, and enhances oxygen storage/release capacity. The carbon conversion to synthesis gas (CCSG) and hydrogen yield are thus enhanced with increasing CeO₂/ZrO₂ mole ratio up to 1:2 and decreased slightly for higher mole ratios. The CCSG and hydrogen yield are also boosted by increasing the amount of nickel in the catalyst up to 20 wt%. 1:2 CeO₂/ZrO₂ mole ratio and 20 wt% nickel content are thus deliberated as optimum. The optimum catalyst exhibits stable catalytic performance for about 30 h time-on-stream. The study further presents the effect of temperature and steam/carbon mole ratio on n-butanol steam reforming.     

Nickel versus cobalt catalysts for hydrogen production by ethanol steam reforming: Ni–Co–Zn–Al catalysts from hydrotalcite-like precursors

The urea hydrolysis method allowed to prepare well-crystallized Ni–Co–Zn–Al Layered Double Hydroxides to be used as precursors of mixed oxide catalysts for the Ethanol Steam Reforming (ESR) reaction. The calcination of the layered precursors gives rise to high surface area mixed oxides, being actually a mixture of a rock salt phase (NiO), a wurtzite phase (ZnO) and a spinel phase.     

Photocatalytic production of hydrogen and methane from glycerol reforming over Pt/TiO2–Nb2O5

In this study, platinized mixed oxides (TiO₂–Nb₂O₅) were tested on photocatalytic hydrogen production from a glycerol solution under UV light. Different samples with different Ti:Nb ratios were prepared by using a simple method that simultaneously combined a physical mixture and a platinum photochemical reduction. This method led to improved physicochemical properties such as low band gap, better Pt nanoparticle distribution on the surface, and the formation of different Pt species. Niobia content was also found to be an important factor in determining the overall efficiency of the Pt–TiO₂–Nb₂O₅ photocatalyst in the glycerol reforming reaction. The photocatalytic results showed that Pt on TiO₂–Nb₂O₅ enhanced hydrogen production from the aqueous glycerol solution at a 5 wt% initial glycerol concentration. The influence of different operating conditions such as the catalyst dosage and initial glycerol concentration was also evaluated. The results indicated that the best hydrogen and methane production was equal to 6657 μmol/L and 194 μmol/L, respectively after 4 h of UV radiation using Pt/Ti:Nb (1:2) sample and with 3 g/L of catalyst dosage. Moreover, the role of water in photocatalytic hydrogen production was studied through photocatalytic activity tests in the presence of D₂O. The obtained results confirmed the role of water molecules on the photocatalytic production of hydrogen in an aqueous glycerol solution.     

Effects of CaO addition on Ni/CeO2–ZrO2–Al2O3 coated monolith catalysts for steam reforming of N-decane

A series of 10 wt%Ni/CeO₂–ZrO₂–Al₂O₃ (10%Ni/CZA) coated monolith catalysts modified by CaO with the addition amount of 1 wt%~7 wt% are prepared by incipient-wetness co-impregnation method. Effects of CaO promoter on the catalytic activity and anti-coking ability of 10%Ni/CZA for steam reforming of n-decane are investigated. The catalysts are characterized by N₂ adsorption-desorption, XRD, SEM-EDS, TEM, NH₃-TPD, XPS, H₂-TPR and Raman. The results show that specific surface area and pore volume of as-prepared catalysts decrease to some extent with the increasing addition of CaO. However, the proper amounts of CaO (≤3 wt%) significantly enhance the catalytic activity in terms of n-decane conversion and H₂ selectivity mainly due to the improved dispersion of NiO particles (precursor of Ni particles). As for anti-coking performance, reducibility of CeO₂ in composite oxide support CZA is promoted by CaO resulting in providing more lattice oxygen, which favors suppressing coke formation. Moreover, the addition of CaO reduces the acidity of 10%Ni/CZA, especially the medium and strong acidity. But far more importantly, a better dispersion of NiO particles obtained by proper amounts of CaO addition is dominant for the lower carbon formation, as well as the higher catalytic activity. For the spent catalysts, amorphous carbon is the main type of coke over 10%Ni–3%CaO/CZA, while abundant filamentous carbon is found over the others.     

Renewable hydrogen production from steam reforming of glycerol by Ni–Cu–Al,Ni–Cu–Mg,Ni–Mg catalysts

H₂ production from glycerol steam reforming by the Ni–Cu–Al, Ni–Cu–Mg, Ni–Mg catalysts was evaluated experimentally in a continuous flow fixed-bed reactor under atmospheric pressure within a temperature range from 450 to 650 °C. The catalysts were synthesized by the co-precipitation methods, and characterized by the elemental analysis, BET, XRD and SEM. The GC and FTIR were applied to analyze the products from steam reforming of glycerol. The coke deposited on the catalysts was measured by TGA experiments during medium temperature oxidation. The results showed that glycerol conversion and H₂ production were increased with increasing temperatures, and glycerol decomposition was favored over its steam reforming at low temperatures. The Ni–Cu–Al catalyst containing NiO of 29.2 wt%, CuO of 31.1 wt%, Al₂O₃ of 39.7 wt% performed high catalytic activity, and the H₂ selectivity was found to be 92.9% and conversion of glycerol was up to 90.9% at 650 °C. The deactivation of catalysts due to the formation and deposition of coke was observed. An improved iterative Coats–Redfern method was used to evaluate the non-isothermal kinetic parameters of coke removal from catalysts, and the results showed the reaction order of n = 1 and 2 in the Fn nth order reaction model predicted accurately the main phase in the coke removal for the regeneration of Ni–Mg and Ni–Cu–Al catalysts, respectively.