Selection of CO2 chemisorbent for fuel-cell grade H2 production by sorption-enhanced water gas shift reaction

New experimental data are reported to demonstrate that high purity H₂ can be directly produced by sorption-enhanced water gas shift (WGS) reaction using synthesis gas (CO + H₂O) as sorber-reactor feed gas. An admixture of a commercial WGS catalyst and a proprietary CO₂ chemisorbent (K₂CO₃ promoted hydrotalcite or Na₂O promoted alumina) was used in the sorber-reactor for removal of CO₂, the WGS reaction by-product, from the reaction zone. The promoted alumina was found to be a superior CO₂ chemisorbent for this application because (a) it could directly produce a fuel-cell grade H₂ product (<10–20 ppm CO) at reaction temperatures of 200 and 400 °C, and (b) it produced ∼45.6% more high purity H₂ product per unit amount of sorbent than the promoted hydrotalcite at 400 °C. Furthermore, the specific fuel-cell grade H₂ productivity by the promoted alumina at a reaction temperature of 200 °C was ∼3.6 times larger than that at 400 °C. These striking differences in the performance of the two CO₂ chemisorbents were caused by the differences in their CO₂ sorption equilibria and kinetics.     

Preparation of highly dispersed Cu/SiO2 doped with CeO2 and its application for high temperature water gas shift reaction

Highly dispersed Cu/SiO₂ catalysts doped with CeO₂ have been successfully prepared via in-situ self-assembled core-shell precursor route. The prepared catalysts were characterized by XRD, SEM, TPR, chemisorption and XPS techniques. The results showed that our newly developed method could not only prepare highly dispersed supported metal catalysts but also highly dispersed supported CeO₂ on silica. The highly dispersed CeO₂ showed strong interaction with highly dispersed Cu. The synergy between the highly dispersed CeO₂ and the highly dispersed Cu exhibited high catalytic activity for high temperature water gas shift reaction compared to the catalysts prepared with the routine method of incipient impregnation.     

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H₂ production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H₂ and N₂) and mixtures (H₂ with N_2, CO or CO₂) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5, while it decreases until 0.66–1.35·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H₂–18%CO–12%CO₂) and a stoichiometric H₂O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h⁻¹. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.     

High temperature water gas shift reaction over promoted iron based catalysts prepared by pyrolysis method

In this work the effects of different promoters (Cr, Al, Mn, Ce, Ni, Co and Cu) on the structural and catalytic properties of Nanocrystalline iron based catalysts for high temperature water gas shift reaction were investigated. The catalysts were prepared in active phase (Fe₃O₄) via a facile direct synthesis routs without any additive and characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR), transmission and scanning electron microscopies (TEM,SEM) techniques. The obtained results indicated that synergic effect of Mn and Ni promoters can lead to obtain a Cr-free catalyst with high activity. In addition, the effect of Ni content on the structural and catalytic properties of the Fe–Mn–Ni catalysts was investigated. It was found that Fe–Mn–Ni catalyst with Fe/Mn = 10 and Fe/Ni = 5 weight ratios showed the highest catalytic activity among the prepared catalysts and possessed a stable catalytic performance without any decrease during 10 h time on stream. Moreover, the effect of GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.     

Activity,stability and deactivation behavior of Au/CeO2 catalysts in the water gas shift reaction at increased reaction temperature (300 °C)

The effect of increasing the reaction temperature to 300 °C on the activity, stability and deactivation behavior of a 4.5 wt.% Au/CeO₂ catalyst in the water gas shift (WGS) reaction in idealized reformate was studied by kinetic and spectroscopic measurements at 300 °C and comparison with previously reported data for reaction at 180 °C under similar reaction conditions [A. Karpenko, Y. Denkwitz, V. Plzak, J. Cai, R. Leppelt, B. Schumacher, R.J. Behm, Catal. Lett. 116 (2007) 105]. Different procedures for catalyst pretreatment were used, including annealing at 400 °C in oxidative, reductive or inert atmospheres as well as redox processing. The formation/removal of stable adsorbed reaction intermediates and side products (surface carbonates, formates, OH_ad, CO_ad) was followed by in situ IR spectroscopy (DRIFTS), the presence of differently oxidized surface species (Au⁰, Au^0′, Au³⁺, Ce³⁺) was evaluated by XPS. The reaction characteristics at 300 °C generally resemble those at 180 °C, including (i) significantly higher reaction rates, (ii) comparable apparent activation energies (44 ± 1/50 ± 1 kJ mol⁻¹ vs. 40 ± 1 kJ mol⁻¹ at 180 °C), (iii) a correlation between deactivation of the catalyst and the build-up of stable surface carbonates, and (iv) a decrease of the initially significant differences in activity after different pretreatment procedures with reaction time. Different than expected, the tendency for deactivation did not decrease with higher temperature, due to enhanced carbonate decomposition, but increases.     

Water-gas shift reaction over CuO/CeO2 catalysts: Effect of CeO2 supports previously prepared by precipitation with different precipitants

A series of CeO₂ supports were firstly prepared by precipitation method with NH₃⋅H₂O (NH), (NH₄)₂CO₃ (NC) and K₂CO₃ (KC) as precipitant, respectively, and then CuO/CeO₂ catalysts were fabricated by depositing CuO on the as-obtained CeO₂ supports by deposition-precipitation method. The effect of CeO₂ supports prepared from different precipitants on the catalytic performance, physical and chemical properties of CuO/CeO₂ catalysts was investigated with the aid of XRD, N₂-physisorption, N₂O chemisorption, FT-IR, TG, H₂-TPR, CO₂-TPD and cyclic voltammetry (CV) characterizations. The CuO/CeO₂ catalysts were examined with respect to their catalytic performance for the water-gas shift reaction, and their catalytic activities and stabilities are ranked as: CuO/CeO₂-NH > CuO/CeO₂-NC > CuO/CeO₂-KC. Correlating to the characteristic results, it is found that the CeO₂ support prepared by precipitation with NH₃⋅H₂O as precipitant (i.e., CeO₂-NH-300) has the best thermal stability and least surface “carbonate-like” species, which make the corresponding CuO/CeO₂-NH catalyst presents the highest Cu-dispersion, the highest microstrain (i.e., the highest surface energy) of CuO, the strongest reducibility and the weakest basicity. While, the precipitants that contain CO₃^2- (e.g. (NH₄)₂CO₃ and K₂CO₃) result in more surface “carbonate-like” species of CeO₂ supports and CuO/CeO₂ catalysts. As a result, CuO/CeO₂-NC and CuO/CeO₂-KC catalysts present poor catalytic performance.     

Kinetics of the water-gas shift reaction over a La0.7Ce0.2FeO3 perovskite-like catalyst using simulated coal-derived syngas at high temperature

The kinetics of the water-gas shift (WGS) reaction over a novel La_0.7Ce_0.2FeO₃ perovskite-like catalyst is investigated using simulated coal-derived syngas at temperatures of 550 °C and 600 °C which are higher than the maximum operating temperature limit for conventional high temperature WGS catalysts. The influences of CO, CO₂, H₂O and H₂ concentration on WGS reaction rate are determined using selected gas compositions that might be encountered in a coal-based gasification system. An empirical power-law rate model used in this study is found to correlate well with experimental data with good accuracy. Kinetics parameters over La_0.7Ce_0.2FeO₃ obtained in this study are mostly in agreement with those previously measured using Fe-Cr based commercial catalysts in a range of relatively lower temperatures (300-500 °C).     

Effect of SiO2-ZrO2 supports prepared by a grafting method on hydrogen production by steam reforming of liquefied natural gas over Ni/SiO2-ZrO2 catalysts

SiO₂-ZrO₂ supports with various zirconium contents are prepared by grafting a zirconium precursor onto the surface of commercial Carbosil silica. Ni(20 wt.%)/SiO₂-ZrO₂ catalysts are then prepared by an impregnation method, and are applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of SiO₂-ZrO₂ supports on the performance of the Ni(20 wt.%)/SiO₂-ZrO₂ catalysts is investigated. SiO₂-ZrO₂ prepared by a grafting method serves as an efficient support for the nickel catalyst in the steam reforming of LNG. Zirconia enhances the resistance of silica to steam significantly and increases the interaction between nickel and the support, and furthermore, prevents the growth of nickel oxide species during the calcination process through the formation of a ZrO₂-SiO₂ composite structure. The crystalline structures and catalytic activities of the Ni(20 wt.%)/SiO₂-ZrO₂ catalysts are strongly influenced by the amount of zirconium grafted. The conversion of LNG and the yield of hydrogen show volcano-shaped curves with respect to zirconium content. Among the catalysts tested, the Ni(20 wt.%)/SiO₂-ZrO₂ (Zr/Si = 0.54) sample shows the best catalytic performance in terms of both LNG conversion and hydrogen yield. The well-developed and pure tetragonal phase of ZrO₂-SiO₂ (Zr/Si = 0.54) appears to play an important role in the adsorption of steam and subsequent spillover of steam from the support to the active nickel. The small particle size of the metallic nickel in the Ni(20 wt.%)/SiO₂-ZrO₂ (Zr/Si = 0.54) catalyst is also responsible for its high performance.     

Photocatalytic H2 production from acetic acid solution over CuO/SnO2 nanocomposites under UV irradiation

The CuO/SnO₂ composites have been prepared by the simple co-precipitation method and further characterized by the XRD, FESEM and Raman spectroscopy. The photocatalytic H₂ production from acetic acid (HAc) solution over CuO/SnO₂ photocatalyst has been investigated at room temperature under UV irradiation. Effects of CuO loading, photocatalyst concentration, acetic acid concentration and pH on H₂ production have been systematically studied. Compared with pure SnO₂, the 33.3 mol%CuO/SnO₂ composite exhibited approximately twentyfold enhancement of H₂ production. The H₂ yield is about 0.66 mol-H₂/mol-HAc obtained under irradiation for prolonged time. The Langmuir-type model is applied to study the dependence of hydrogen production rate on HAc concentration. A possible mechanism for photocatalytic degradation of acetic acid over CuO/SnO₂ photocatalyst is proposed as well. Our results provide a method for pollutants removal with simultaneous hydrogen generation. Due to simple preparation, high H₂ production activity and low cost, the CuO/SnO₂ photocatalyst will find wide application in the coming future of hydrogen economy.     

A highly active and stable chromium free iron based catalyst for H2 purification in high temperature water gas shift reaction

In this work mesoporous nanocrystalline chromium free Fe–Al–Ni catalysts with various Fe/Al and Fe/Ni ratios were prepared by coprecipitation method for high temperature water gas shift reaction. The prepared catalysts were characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM) techniques. The catalytic results revealed that the catalyst with Fe/Al = 10 and Fe/Ni = 5 weight ratios exhibited the highest catalytic activity among the prepared catalysts and the commercial chromium containing one. This catalyst possessed a high surface area of 177.4 m² g⁻¹ with an average pore size of 4.3 nm with a high stability during 20 h time on stream. Furthermore, the effect of calcination temperature, GHSV and steam/gas ratio on the structural properties and catalytic performance of the catalyst with the highest activity was investigated.     

Low temperature CO oxidation and water gas shift reaction over Pt/Pd substituted in Fe/TiO2 catalysts

We demonstrate the activity of Ti_0.84Pt_0.01Fe_0.15O_2−δ and Ti_0.73Pd_0.02Fe_0.25O_2−δ catalysts towards the CO oxidation and water gas shift (WGS) reaction. Both the catalysts were synthesized in the nano crystalline form by a low temperature sonochemical method and characterized by different techniques such as XRD, FT-Raman, TEM, FT-IR, XPS and BET surface analyzer. H₂-TPR results corroborate the intimate contact between noble metal and Fe ions in the both catalysts that facilitates the reducibility of the support. In the absence of feed CO₂ and H₂, nearly 100% conversion of CO to CO₂ with 100% H₂ selectivity was observed at 300 °C and 260 °C respectively, for Ti_0.84Pt_0.01Fe_0.15O_2−δ and Ti_0.73Pd_0.02Fe_0.25O_2−δ catalyst. However, the catalytic performance of Ti_0.73Pd_0.02Fe_0.25O_2−δ deteriorates in the presence of feed CO₂ and H₂. The change in the support reducibility is the primary reason for the significant increase in the activity for CO oxidation and WGS reaction. The effect of Fe addition was more significant in Ti_0.73Pd_0.02Fe_0.25O_2−δ than Ti_0.84Pt_0.01Fe_0.15O_2−δ. Based on the spectroscopic evidences and surface phenomena, a hybrid reaction scheme utilizing both surface hydroxyl groups and the lattice oxygen was hypothesized over these catalysts for WGS reaction. The mechanisms based on the formate and redox pathway were used to fit the kinetic data. The analysis of experimental data shows the redox mechanism is the dominant pathway over these catalysts.     

Monolithic Pt/Ce0.8Zr0.2O2/cordierite catalysts for low temperature water gas shift reaction in the real reformate

Monolithic catalysts were prepared by washcoating Ce_0.8Zr_0.2O₂ slurries and then impregnating platinum or rhenium onto cordierite substrates, and characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), inductively coupled plasma (ICP), temperature-programmed-reduction (TPR) and temperature-programmed deposition of CO (CO-TPD) techniques. The effects of preparation parameters on the catalytic performance for water gas shift (WGS) reaction were investigated in details, including different Ce_0.8Zr_0.2O₂ powder as washcoat, coat loadings, metal loadings, Pt/Re weight ratio and impregnation sequences. In addition, pyrophoricity (exposure to oxygen stream) and long-term stability were carried out over monolithic catalysts with the optimized composition. The results showed that Ce_0.8Zr_0.2O₂ prepared by microemulsion methods was the preferred washcoat, and that 50 wt% Ce_0.8Zr_0.2O₂ coat loading and 0.68 wt% Pt loading were required to reduce CO content to ca. 1%. The optimal catalytic performance was achieved over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst. Pyrophoricity tests indicated that no obvious activity loss was observed over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst after three exposures to oxygen; while 17% of the initial activity was lost over industrial B206 after one exposure. Monolithic 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst exhibited good stability during 80 h on-stream test.     

High performance of bulk Mo2N and Co3Mo3N catalysts for hydrogen production from ammonia: Role of citric acid to Mo molar ratio in preparation of high surface area nitride catalysts

Hydrogen production from ammonia decomposition was studied using a series of unsupported high surface area molybdenum nitride (Mo₂N) and cobalt promoted molybdenum nitride (3%Co-Mo₂N) catalysts prepared with citric acid (CA) as a chelating agent. To elucidate the influence of citric acid amount in preparation conditions on the structure and catalytic activity, we prepared catalysts with different citric acid to Mo molar ratios i.e. CA/Mo = 1, 2, 3 and 4. The catalytic activity was evaluated in the temperature range of 300–600 °C at atmospheric pressure. The catalytic activity of the tested samples has changed in the following order of CA/Mo atomic ratio of 1 < 2 < 3 > 4. Therefore, the catalyst prepared by using CA/Mo ratio = 3 showed the highest catalytic activity. BET, XRD, XPS, SEM and TEM-EDS techniques were been used to characterize the catalysts. The increased activity of Mo₂N-3:1 and 3%Co-Mo₂N-3:1 catalysts was due to increased surface area, decreased particle size and increased relative proportions of Mo₂N and Co₃Mo₃N phases. The ammonia conversion for 3%Co-Mo₂N catalyst was increased from 75 to 97% at 550 °C with the increase of CA/Mo ratio from 1 to 3. This enrichment of activity in 3%Co-Mo₂N-3:1 catalyst is due to increased dispersion of Co₃Mo₃N microstructure on γ-Mo₂N platelets confirmed by SEM and TEM results. No deactivation was observed for any catalysts investigated in this study for ammonia decomposition.     

CO removal via selective methanation over the catalysts Ni/ZrO2 prepared with reduction by the wet H2-rich gas

The wet H₂-rich gas was used as reducing gas instead of the H₂/N₂ gas in the reduction step of the catalyst preparation. It is found that the selectivity for CO methanation over the catalysts 0.4Ni/ZrO₂ so-obtained was decreased in comparison to the case of the H₂/N₂ gas used as reducing gas. Even though, the samples with the different feed atomic ratios of Ni/Zr prepared by the impregnation method and the co-precipitation method, respectively, were evaluated with the wet H₂-rich gas both as reducing gas and as reactant gas. The catalysts Ni/ZrO₂-CP prepared by the co-precipitation method exhibited a high catalytic activity for CO removal at a lowered reaction temperature with increasing the Ni loading. Over the catalyst 3.0Ni/ZrO₂-CP, CO in the reactant gas could be removed to below 10 ppm at reaction temperatures of 220–260 °C with the selectivity higher than 50%. And the selectivity was kept at 100% during the 100 h test at 220 °C. The catalysts were characterized by XRD, XPS, XRF and the adsorption isotherm measurement. In addition, effect of water vapor in reactant gas was studied over the catalysts 0.4Ni/ZrO₂ with the wet H₂-rich gas and the dry H₂-rich gas as reactant gas, respectively, in the case of the H₂/N₂ gas fixed as reducing gas. It is seen that presence of water vapor in the reactant gas retarded methanation reactions of CO and CO₂ on the catalysts.     

Effects on CHP plant efficiency of H2 production through partial oxydation of natural gas over two group VIII metal catalysts

Blending H₂ with natural gas in spark ignition engines can increase for electric efficiency. In-situ H₂ production for spark ignition engines fuelled by natural gas has therefore been investigated recently, and reformed exhaust gas recirculation (RGR) has been identified a potentially advantageous approach: RGR uses the steam and O₂ contained in exhaust gases under lean combustion, for reforming natural gas and producing H₂, CO, and CO₂. In this paper, an alternative approach is introduced: air gas reforming circulation (AGRC). AGRC uses directly the O₂ contained in air, rendering the chemical pathway comparable to partial oxidation. Formulations based on palladium and platinum have been selected as potential catalysts. With AGRC, the concentrations of the constituents of the reformed gas are approximately 25% hydrogen, 10% carbon monoxide, 8% unconverted hydrocarbons and 55% nitrogen. Experimental results are presented for the electric efficiency and exhaust gas (CO and HC) composition of the overall system (SI engine equipped with AGRC). It is demonstrated that the electric efficiency can increase for specific ratios of air to natural gas over the catalyst. Although the electric efficiency gain with AGRC is modest at around 0.2%, AGRC can be cost effective because of its straightforward and inexpensive implementation. Misfiring and knock were both not observed in the tests reported here. Nevertheless, technical means of avoiding knock are described by adjusting the main flow of natural gas and the additional flow of AGRC.     

Enhanced photocatalytic H2 production from glycerol solution over ZnO/ZnS core/shell nanorods prepared by a low temperature route

A series of ZnO/ZnS core/shell nanorods with different ZnS/ZnO molar ratios was synthesized via a new water bath route. The nanorods have a diameter of about 100 nm and a length ranging from a few hundred nanometers to several micrometers. They are formed by coating ZnO nanorod with a layer of porous ZnS shell mainly consisting of crystals which are about 12 nm in diameter. The results showed that the deposition thickness of the ZnS shell layer strongly affected the morphologies, surface area, structure, photo absorption and photocatalytic performance of the ZnO/ZnS core/shell nanorods. The as-prepared ZnO/ZnS core/shell nanorods exhibited a higher photocatalytic activity for H₂ evolution from the glycerol/water mixtures compared with the ZnO nanorods under the same conditions. The maximum H₂ production was 2608.7 and 388.4 μmol h⁻¹ gcat⁻¹ under UV and solar-simulated light irradiation and the corresponding quantum efficiencies were 22% and 13%, respectively. The deposition thickness of the ZnS shell and the interaction between the ZnO rod and ZnS shell and the core/shell structure with n-p heterojunction substantially influence the optical and catalytic performance of the ZnO/ZnS core/shell nanorods.     

Effect of treatment temperature on the performance of RuO2 anode electrocatalyst for high temperature proton exchange membrane water electrolysers

Ruthenium oxide catalysts were prepared by a sol–gel technique and calcined at different temperatures e.g., 400 °C, 500 °C and 600 °C. The catalysts performance for the oxygen evolution reaction was studied using cyclic voltammetry and their performance in a high temperature proton exchange membrane water electrolyser (PEMWE) examined. Physio-chemical characterization was carried out to study the thermal stability, oxygen-metal bond formation, crystallinity phase and crystallite size, particle size and elemental analysis by TGA, FTIR, XRD, TEM and EDX respectively. The electrolyte used for electrochemical characterisation was 1.0 M H₃PO₄ and 0.5 M H₂SO₄. Additionally, the effect of calcination and electrolyte temperature on oxygen evolution reaction of RuO₂ catalysts was studied and the apparent activation energy was determined using chronoamperometry. The prepared RuO₂ were tested as anode catalyst in PEMWE in the temperature range of 120–150 °C using phosphoric acid doped polybenzimidazole membrane electrolyte. The physio-chemical and electrochemical characterization results indicate that RuO₂ calcined at 500 °C gave the best performance with a current density of 0.875 A cm⁻² at 1.8 V in a PEMWE operated at 150 °C.     

Performance of Na2O promoted alumina as CO2 chemisorbent in sorption-enhanced reaction process for simultaneous production of fuel-cell grade H2 and compressed CO2 from synthesis gas

The performance of a novel thermal swing sorption-enhanced reaction (TSSER) concept for simultaneous production of fuel-cell grade hydrogen and compressed carbon dioxide as a by-product from a synthesis gas feed is simulated using Na₂O promoted alumina as a CO₂ chemisorbent in the process. The process simultaneously carries out the water gas shift (WGS) reaction and removal of CO₂ from the reaction zone by chemisorption in a single unit. Periodic regeneration of the chemisorbent is achieved by using the principles of thermal swing adsorption employing super-heated steam purge.     

Modulating the textural properties and photocatalytic hydrogen production activity of TiO2 by high temperature supercritical drying

We report a facile method for the synthesis of TiO₂ aerogels by a single step high temperature supercritical drying (HTSCD) of sol–gel derived TiO₂. The morphological and structural features of the resultant materials were determined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, Diffuse Reflectance (DR) spectra, and Fourier Transform infra-Red spectroscopy (FT-IR) measurements. The materials exhibited enhanced solar hydrogen production from water using methanol as sacrificial reagent under Ultra-Violet (UV) light in the absence of Pt as a co-catalyst. Among the TiO₂ aerogel samples synthesized, TiO₂-M-6h evolved 390 μmol g⁻¹ of H₂ after 4 h of irradiation, whereas TiO₂-M-2h produced 217 μmol g⁻¹ of H₂ after 4 h of irradiation under identical conditions, indicating the importance of aging the gels prior to HTSCD step. The enhancement was credited to increase in surface area, and decrease in particle size in TiO₂-M-6h as evidenced from N₂-sorption and DRS studies respectively. Upon comparison with a room temperature synthesized TiO₂-xerogel, the aerogel materials exhibited enhanced hydrogen production. The results validate the superior performance of TiO₂ aerogel materials over TiO₂ xerogels and indicate the potential of HTSCD method for the preparation of titania aerogels for solar energy applications.     

Effect of biomass leaching on H2 production,ash and tar behavior during high temperature steam gasification (HTSG) process

The effect of biomass water leaching on H₂ production, as well as, prediction of ash thermal behavior and formation of biomass tar during high temperature steam gasification (HTSG) of olive kernel is the main aim of the present work. Within this study raw olive kernel samples (OK₁, OK₂) and a pre-treated one by water leaching (LOK₂) were examined with regard to their ash fouling propensity and tar concentration in the gaseous phase. Two temperatures (T = 850 and 950 °C) and a constant steam to biomass ratio (S/B = 1.28) were chosen in order to perform the steam gasification experiments. Results indicated that considering the samples' ash thermal behavior, it seemed that water leaching improved the fusibility behavior of olive kernel; however, it proved that water leaching does not favour tar steam reforming, while at the same time decreases the H₂ yield in gas product under air gasification conditions, due to possible loss of the catalytic effect of ash with water leaching.