Hydrogen production from glycerol steam reforming over molybdena–alumina catalysts

The glycerol steam reforming was investigated on alumina supported molybdena catalysts (with 2, 5 and 12 wt.%) prepared by the sol–gel method and gel combustion. The catalysts were characterized by XRD, BET, UV–VIS, DRIFT, SEM and TEM. The catalytic performances were studied at 400–500 °C, steam to glycerol molar ratio between 9:1 and 20:1 and feed flow rate 0.04–0.08 ml/min. The conversion is directly proportional to molybdena loading, while the hydrogen selectivity has reached greater value on catalyst with 2% MoO₃. The optimum ratio steam to glycerol for reforming is 15:1 and for decomposition in syngas 9:1 and the ratio 20:1 favors water gas shift reaction.     

Hydrogen production by sorption-enhanced steam methane reforming process using CaO-Zr/Ni bifunctional sorbent–catalyst

A bifunctional CaO-Zr/Ni (13, 18, and 20.5 wt% NiO) sorbent–catalyst was developed using the wet-mixing/sonication technique and applied for hydrogen production by sorption-enhanced steam methane reforming (SESMR), an intensified process that integrates hydrogen production with CO₂ capture. The material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N₂ physisorption (BET). CO₂ sorption efficiency of the developed materials was evaluated during 25 CO₂ sorption/regeneration cycles. The prepared sorbent–catalysts were then applied in the SESMR during 10 reaction cycles. The results showed that the bifunctional sorbent–catalyst with 20.5 wt% NiO loading presented the most suitable activity. The H₂ yield of ∼91% at the end of the 10th SESMR cycle is considerably higher than equilibrium H₂ yield that could be obtained by traditional steam methane reforming.     

Kinetics of methane combustion over Pt and Pt–Pd catalysts

A kinetic study was performed over thermally aged and steam-aged Pt and Pt–Pd catalysts to investigate the effect of temperature, and methane and water concentrations on the performance of catalysts in the range of interest for environmental applications. It was found that both catalysts permanently lose a large portion of their initial activity as result of exposure to 5 vol.% water in the reactor feed. Empirical power-law and LHHW type of rate equations were proposed for methane combustion over Pt and Pt–Pd catalysts respectively. Optimization was used to determine the parameters of the proposed rate equations using the experimental results. The overall reaction orders of one and zero in methane and water concentration was found for stabilized steam-aged Pt catalyst in the presence and absence of water. The apparent self-inhibition effect caused by methane over Pt–Pd catalyst in the absence of water was associated with the inhibiting effect of water produced during the combustion of methane. A significant reversible inhibition effect was also observed over steam-aged Pt–Pd catalyst when 5 vol.% water vapor was added to the reactor feed stream. A significant reduction in both activity and activation energy was observed above temperatures of approximately 550 °C for steam-aged Pt–Pd catalyst in the presence of water (the activation energy dropped from a value of 72.6 kJ/mol to 35.7 kJ/mol when temperature exceeded 550 °C).     

Nickel–magnesia catalysts for the steam reforming of light hydrocarbons

The advantages of using magnesia prepared using two techniques as a support for nickel catalysts for the steam reforming of light hydrocarbons has been examined. The initial specific activities of nickel supported on alumina or magnesia were similar, but deactivation as a result of coke formation was significantly greater on alumina-supported nickel. The steam reforming of ethane and propane over nickel/magnesia catalysts was much less affected by coke formation over longer times-on-line. The effects of variation in the preparation of magnesia were small, differences only appearing in rates of coking of higher hydrocarbons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synergetic effect of combined use of Cu–ZnO–Al2O3 and Pt–Al2O3 for the steam reforming of methanol

Commercial Cu–ZnO–Al₂O₃ catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al₂O₃ catalyst with Pt–Al₂O₃ catalyst. The Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture was used.     

Renewable hydrogen production from steam reforming of glycerol (SRG) over ceria-modified γ-alumina supported Ni catalyst

Excess crude glycerol derived as a by-product from biodiesel industry prompts the need to valorise glycerol to value-added chemicals. In this context, catalytic steam reforming of glycerol (SRG) was proposed as a promising and sustainable alternative for producing renewable hydrogen (H₂). Herein, the development of nickel (Ni) supported on ceria-modified mesoporous γ-alumina (γ-Al₂O₃) catalysts and their applications in catalytic SRG (at 550–750 °C, atmospheric pressure and weight hourly space velocity, WHSV, of 44,122 ml·g⁻¹·h⁻¹ (STP)) is presented. Properties of the developed catalysts were characterised using many techniques. The findings show that ceria modification improved Ni dispersion on γ-Al₂O₃ catalyst support with highly active small Ni particles, which led to a remarkable catalytic performance with the total glycerol conversion (ca. 99%), glycerol conversion into gaseous products (ca. 77%) and H₂ yield (ca. 62%). The formation rate for H₂ production (14.4 × 10⁻⁵ mol·s⁻¹·g⁻¹, TOF (H₂) = 3412 s⁻¹) was significantly improved with the Ni@12Ce-Al₂O₃ catalyst, representing nearly a 2-fold increase compared with that of the conventional Ni@Al₂O₃ catalyst. In addition, the developed catalyst also exhibited comparatively high stability (for 12 h) and coke resistance ability.     

Production of hydrogen via combined steam reforming of methanol over CuO–CeO2 catalysts

Hydrogen production by (combined) steam reforming of methanol (CSRM) was investigated over CuO–CeO₂ catalysts prepared via the urea-combustion method. The characteristics of the resulting oxides were strongly influenced by the autoignition time during synthesis and the sample prepared with near stoichiometric quantity of urea had less favorable catalytic properties. Catalysts prepared from urea-rich or lean mixtures were more active and selective and an optimum behavior was obtained with 75% excess of urea and Cu/(Cu + Ce) ratio equal to 0.15. The higher methanol conversion in the CSRM process may be attributed to more efficient heat transfer in the bed due to combustion of part of methanol.     

Influence of ambient gas on microwave-assisted combustion synthesis of CuO–ZnO–Al2O3 nanocatalyst used in fuel cell grade hydrogen production via methanol steam reforming

The effect of different ambient gases for preparation of CuO-ZnO-Al₂O₃ nanocatalysts by the microwave assisted solution combustion method was studied. Air, nitrogen and carbon dioxide as the ambient atmospheres were injected during the solution combustion synthesis method. The fabricated nanocatalysts were characterized by various techniques such as XRD, FESEM, TEM, EDX, FTIR and BET analyses. It was understood that injection of nitrogen during synthesis of nanocatalysts led to high dispersion of Cu crystallites as the active sites for the steam methanol reforming reaction. Moreover, appropriate interaction between CuO and ZnO particles was achieved due to better morphology of the nanocatalyst synthesized by N₂ as the ambient gas than other samples. Finally, high methanol conversion with proper products selectivity were achieved by the nanocatalyst synthesized by injection of N₂ during the microwave assisted combustion synthesis method due to significant superiority in its physicochemical properties.     

Propane dehydrogenation activity of Pt and Pt–Sn catalysts supported on magnesium aluminate: influence of steam and hydrogen

Propane dehydrogenation was carried out in hydrogen and steam as reaction media on Pt/MgAl₂O₄ and Pt–Sn/ MgAl₂O₄ catalysts. A wide range of Pt and Pt–Sn concentrations was explored. Monometallic Pt catalysts were completely poisoned by steam. Concerning bimetallic Pt–Sn catalysts, tin played an important role related to the activation of platinum particles when the reaction was carried out in steam. On the other hand, tin inhibited cracking reactions leading to an increase of catalysts stability. Activation energy in hydrogen was the same for monometallic and bimetallic catalysts: 22 kcal/mol; while for the reaction in steam, values ranging from 10 to 15 kcal/mol were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Steam reforming of methanol over Pt–Zn alloy catalyst supported on carbon black

Steam reforming of methanol over Zn-promoted Pt catalyst supported on an electrically conductive carbon black has been investigated after H₂ reduction at 873 K. X-ray diffraction measurement showed that Pt–Zn alloy was formed on the carbon black (C). The Zn-promoted Pt/C catalyst showed higher activity and selectivity to CO₂ compared with unpromoted Pt/C catalyst. Methyl formate was formed over the Zn-promoted Pt/C catalyst in decomposition of methanol (without water). This suggests that steam reforming of methanol over the Zn-promoted Pt/C catalyst can proceed via methyl formate, which is different from that of the unpromoted Pt/C catalyst.     

Synergistic bimetallic Ru–Pt catalysts for the low-temperature aqueous phase reforming of ethanol

Aqueous phase reforming (APR) of ethanol has been studied over a series of Ru and Pt catalysts supported on carbon and titania, with different metal loadings and particle sizes. This study proposed that, on both metals, ethanol is first dehydrogenated to acetaldehyde, which subsequently undergoes C C cleavage followed by different paths, depending on the catalyst used. For instance, although monometallic Pt has high selectivity toward H₂ via dehydrogenation, it has a low efficiency for C C cleavage, lowering the overall H₂ yield. Large Ru particles produce CH₄ through methanation, which is undesirable because it consumes H₂. Small Ru particles have lower activity but higher selectivity toward H₂ rather than CH₄. On these small particles, CO blocks low-coordination sites, inhibiting methanation. The combination of the two metals in bimetallic Ru–Pt catalysts results in improved performance, benefiting from the desirable properties of each Ru and Pt, without the negative effects of either. © 2018 American Institute of Chemical Engineers AIChE J, 65: 151–160, 2019     

Mechanism of CH4 Dry Reforming on Nanocrystalline Doped Ceria-Zirconia with Supported Pt, Ru, Ni, and Ni–Ru

Specificity of CH₄ dry reforming mechanism for Me-supported doped ceria-zirconia catalysts with high oxygen mobility was elucidated using a combination of transient kinetic methods (TAP, SSITKA) with pulse microcalorimetry and in situ FTIRS. Steady-state reaction of CH₄ dry reforming is described by a simple redox scheme with independent stages of CH₄ and CO₂ activation. This is provided by easy CO₂ dissociation on reduced sites of oxide supports followed by a fast oxygen transfer along the surface/domain boundaries to metal sites where CH₄ molecules are transformed to CO and H₂. The rate-limiting stage is irreversible transformation of CH₄ on metal sites, while CO₂ transformation proceeds much faster being reversible for steady-state surface. The oxygen forms responsible for CH₄ selective transformation into syngas correspond to strongly bound bridging oxygen species with heats of desorption ≈600–650 kJ/mol O₂, most probably bound with pairs of Pr and/or Ce cations able to change their oxidation state. Ni + Ru clusters could be involved in CO₂ activation via facilitating C–O bond breaking in the transition state, thus increasing the rate constant of the surface reoxidation by CO₂. Strongly bound carbonates are spectators.     

Highly dispersed sol–gel synthesized Cu–ZrO2 materials as catalysts for oxidative steam reforming of methanol

New nanodispersed Cu–ZrO₂ systems (containing 0 and 8.3 mol% Cu) were synthesized by sol–gel method. Homogeneous gels were prepared starting from Zr propoxide and Cu(NO₃)₂·2.5H₂O. The materials were characterized by XRD, TG/DTA, N₂ adsorption, TPR techniques and N₂O surface oxidation. In the Cu-containing material part of Cu²⁺ ions were incorporated into the zirconia lattice and strongly influenced the crystallisation behaviour of zirconia matrix. After treatment at 450–600 °C, the materials contained ZrO₂ nanocrystals of the tetragonal polymorph. The samples heat treated up to 450 °C showed high surface areas in the range 140–180 m²/g. Copper oxide species with different reducibility were detected by TPR measurements. The H₂ reduction treatments gave rise to metallic copper with very high dispersion. The catalysts showed high activity for the oxidative steam reforming of methanol. A noticeable activity was observed also with the not pre-reduced catalyst, although a previous reduction in H₂ led to a higher selectivity and H₂ production.     

Mechanistic studies of CO2/CH4 reforming over Ni–La2O2/5A

The mechanism of CO₂/CH₄ reforming over Ni–La₂O₃/5A has been studied. The results of the CO₂‐pulsing experiments indicated that the amount of CO₂ converted was roughly proportional to the amount of H present on the catalyst, implying that CO₂ activation could be H‐assisted. Pulsing CH₄ onto a H₂‐reduced sample and a similar sample pretreated with CO₂, we found that CH₄ conversion was higher in the latter case. Hence, the idea of oxygen‐assisted CH₄ dissociation is plausible. The fact that the amount of CO produced in 10 pulses of CO₂/CH₄ was larger than that produced in 5 pulses of CO₂ followed by 5 pulses of CH₄, indicated that CO₂ and CH₄ could activate each other synergistically. In the chemical trapping experiments, following the introduction of CD₃I onto a Ni–La₂O₃/5A sample pretreated with CH₄/CO₂, we observed CD₃COOH, CD₃CHO, and CD₃OCD₃. In the in situ DRIFT experiments, IR bands attributable to formate and formyl were observed under working conditions. These results indicate that formate and formyl are intermediates for syngas generation in CO₂/CH₄ reforming, and active O is generated in the breaking of a C–O bond. Based on these results, we suggest that during CO₂/CH₄ reforming, CO₂ activation is H‐promoted and surface O species generated in CO₂ dissociation reacts with CH_x to give CO. A reaction scheme has been proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modeling the reforming of straight-run gasoline (fraction 85–140°C) with allowance for the deactivation of Pt catalyst

A kinetic model of reforming is developed that describes the chemical transformations of С₆–С₈ pseudocomponents over Pt catalyst. The composition of platformate is predicted in light of the activity of the metal and acid sites, and temperature profile in the reactors. Equations of mass and heat balance are used in the calculations. The rate constants and activation energies of individual reactions are determined for catalyst of the R-134 series. The stationary activity values (a _s = 0.8) are calculated along with the constants of the deactivation of acid (0.0056 ± 0.0004 min^?1) and metal (0.079 ± 0.003 min^?1) sites at Т = 490°C. The relative error of platformate composition modeling for benzene, toluene, and xylenes does not exceed 5%. It is shown that the stability of platformate composition is due to a stepwise temperature increase in the reactors during the periods between regenerations. It is proposed that the developed model be used to select temperature regimes for the operation of aromatic-producing industrial complexes in order to obtain platformate of desired compositions.     

Esterification of fatty acids with glycerol over Fe–Zn double-metal cyanide catalyst

Solid Fe–Zn double-metal cyanide (DMC) complex exhibits high catalytic activity for esterification of fatty acids (FA) with glycerol. DMC catalysts with varying acidities were prepared by synthesizing the material at four different temperatures (10, 25, 50 and 80 °C). The catalyst prepared at 50 °C exhibited highest catalytic activity. Catalytic activity of DMC was influenced by both acidity and surface area. Complete conversion of FA was achieved at 140–200 °C under atmospheric pressure. Chain length of FA was found to influence the rate of reaction and product selectivity.     

Effect of steam content and O2 pretreatment on the catalytic activities of Au/CeO2–Fe2O3 catalysts for steam reforming of methanol

The Au/CeO₂–Fe₂O₃ prepared by deposition–precipitation were studied by steam reforming of methanol at a reaction temperature range of 200–400 °C. Complete methanol conversion was obtained at the optimal steam/methanol ratio of 2 at 400 °C. A high steam content strongly depressed both methanol conversion and hydrogen concentration since this led to a complex mechanism and the formation of carbonate and formate species. After pretreating with oxygen, the catalytic activity dramatically decreased with the presence of an inhomogeneous Ce_xFe_1−xO₂ solid solution phase; the covering Au sites by the free α-Fe₂O₃ particles; and an agglomeration of both free α-Fe₂O₃ and Au particles.     

Characterisation of carbon deposits on Ni/SiO2 in the reforming of CH4–CO2 using fixed- and fluidised-bed reactors

CO₂ reforming of methane was investigated with regard to carbon deposition on 4.5 wt% NiO/SiO₂ catalyst at 1023 K, 1 atm and a CH₄/CO₂ ratio of 1.0 employing micro-fluidised- and fixed-bed reactors. A higher catalytic activity (by 20%) was observed in the initial stage (0.5 h) of the fluidised-bed reforming which may be attributed to lesser deactivation of the catalyst compared to fixed-bed operation. Only a limited amount of carbon was deposited in a period of 11 h on stream. In the case of the fixed-bed reactor, a much larger amount of carbon was found on the spent catalyst, particularly, when sampled from the bottom of the bed. TPO results suggest that carbon deposits on the catalyst samples from the fluidised-bed as well as the top of the fixed-bed are rather small and of similar nature. The carbon deposited at the bottom of the fixed-bed reactor contained two distinct species according to XPS results (corresponding to C–O and C–C bonds).     

Preparation of egg-shell type Ni-loaded catalyst by adopting “Memory Effect” of Mg–Al hydrotalcite and its application for CH4 reforming

Ni-loaded catalyst in egg-shell type was successfully prepared by adopting “Memory Effect” of Mg–Al hydrotalcite-like compounds. Mg–Al mixed oxide particles were prepared by calcination of Mg–Al hydrotalcite and dipped in Ni(II) nitrate aqueous solution. Upon dipping, Mg–Al hydrotalcite was reconstituted in the surface layer of the particle and a part of the Mg sites was replaced by Ni. Finally egg-shell type loaded Ni catalyst was obtained after the calcination followed by the reduction of the particles. The catalyst showed a high and stable activity for autothermal CH₄ reforming due to highly dispersed and stable Ni metal particles concentrated in the catalyst surface layer.