Mechanisms of synthesis gas production via thermochemical cycles over La0·3Sr0·7Co0·7Fe0·3O3

La_0·3Sr_0·7Co_0·7Fe_0·3O₃ (LSCF3773) was chosen as an oxygen carrier material for synthesis gas production and synthesized using ethylene-diamine-tetra-acetic acid (EDTA) citrate-complexing method. LSCF exhibited a pure cubic structure where 110 and 100 plane diffractions were active for CO₂ splitting, while 111 was more favored by H₂O splitting. Overall oxygen storage capacity (OSC) of LSCF was 4072 μmol/g_cat. During the reduction process, regular cations (Co⁴⁺, Fe⁴⁺), polaron cations (Co³⁺, Fe³⁺) and localized cations (Co²⁺, Fe²⁺) were achieved when the LSCF was reduced at 500, 700 and 900 °C, respectively. The strength of the active sites depended on reduction temperatures. An increase in oxidation temperature enhanced H₂ production at temperature ranging from 500 °C to 700 °C while effected CO production at 900 °C. H₂O and CO₂ was competitively split during the oxidation step, especially at 700 °C. The activation energy of each reaction was ordered as; CO₂ splitting > H₂O splitting > CO₂ adsorption, supporting the above evidence where H₂ and CO production were found to increase when the operating temperature was increased.     

Design of a thermally integrated bioethanol-fueled solid oxide fuel cell system integrated with a distillation column

Solid oxide fuel cell systems integrated with a distillation column (SOFC-DIS) have been investigated in this study. The MER (maximum energy recovery) network for SOFC-DIS system under the base conditions (C_EtOH = 25%, EtOH recovery = 80%, V = 0.7 V, fuel utilization = 80%, T_SOFC = 1200 K) yields Q_Cmin = 73.4 and Q_Hmin = 0 kW. To enhance the performance of SOFC-DIS, utilization of internal useful heat sources from within the system (e.g. condenser duty and hot water from the bottom of the distillation column) and a cathode recirculation have been considered in this study. The utilization of condenser duty for preheating the incoming bioethanol and cathode recirculation for SOFC-DIS system were chosen and implemented to the SOFC-DIS (CondBio-CathRec). Different MER designs were investigated. The obtained MER network of CondBio-CathRec configuration shows the lower minimum cold utility (Q_Cmin) of 55.9 kW and total cost index than that of the base case. A heat exchanger loop and utility path were also investigated. It was found that eliminate the high temperature distillate heat exchanger can lower the total cost index. The recommended network is that the hot effluent gas is heat exchanged with the anode heat exchanger, the external reformer, the air heat exchanger, the distillate heat exchanger and the reboiler, respectively. The corresponding performances of this design are 40.8%, 54.3%, 0.221 W cm⁻² for overall electrical efficiency, Combine Heat and Power (CHP) efficiency and power density, respectively. The effect of operating conditions on composite curves on the design of heat exchanger network was investigated. The obtained composite curves can be divided into two groups: the threshold case and the pinch case. It was found that the pinch case which T_SOFC = 1173 K yields higher total cost index than the CondBio-CathRec at the base conditions. It was also found that the pinch case can become a threshold case by adjusting split fraction or operating at lower fuel utilization. The total cost index of the threshold cases is lower than that of the pinch case. Moreover, it was found that some conditions can give lower total cost index than that of the CondBio-CathRec at the base conditions.     

Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

The effect of specific surface area on the activity of nano-scale ceria catalysts for methanol decomposition with and without steam at SOFC operating temperatures

Nano-particulate high surface area CeO₂ was found to have a useful methanol decomposition activity producing H₂, CO, CO₂, and a small amount of CH₄ without the presence of steam being required under solid oxide fuel cell temperatures, 700-1000 °C. The catalyst provides high resistance toward carbon deposition even when no steam is present in the feed. It was observed that the conversion of methanol was close to 100% at 850 °C, and no carbon deposition was detected from the temperature programmed oxidation measurement.The reactivity toward methanol decomposition for CeO₂ is due to the redox property of this material. During the decomposition process, the gas-solid reactions between the gaseous components, which are homogeneously generated from the methanol decomposition (i.e., CH₄, CO₂, CO, H₂O, and H₂), and the lattice oxygen on ceria surface take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen ( can produce synthesis gas (CO and H₂) and also prevent the formation of carbon species from hydrocarbons decomposition reaction (C_nH_m⇔nC+m/2H₂). V_O^·· denotes an oxygen vacancy with an effective charge 2⁺. Moreover, the formation of carbon via Boudouard reaction (2CO⇔CO₂+C) is also reduced by the gas-solid reaction of carbon monoxide with the lattice oxygen .At steady state, the rate of methanol decomposition over high surface area CeO₂ was considerably higher than that over low surface area CeO₂ due to the significantly higher oxygen storage capacity of high surface area CeO₂, which also results in the high resistance toward carbon deposition for this material. In particular, it was observed that the methanol decomposition rate is proportional to the methanol partial pressure but independent of the steam partial pressure at 700-800 °C. The addition of hydrogen to the inlet stream was found to have a significant inhibitory effect on the rate of methanol decomposition.     

Application of a micro-channel reactor for process intensification in high purity syngas production via H2O/CO2 co-splitting

A stainless steel micro-channel reactor was tailor-made to an in house-design for process intensification propose. The reactor was used for a two-step thermochemical cycles of H₂O and CO₂ co-splitting reaction, in the presence of La_0.3Sr_0.7Co_0.7Fe_0.3O₃ (LSCF). LSCF was coated inside the reactor using wash-coat technique. Oxygen storage capacity of LSCF was determined at 4465 μmol/g, using H₂-TPR technique. H₂O-TPSR and CO₂-TPSR results suggested that a formation of surface hydroxyl group was the cause of H₂O splitting favorable behavior of LSCF. Optimal operating reduction/oxidation temperature was found at 700 °C, giving 2266 μmol/g of H₂, 705 μmol/g of CO, and 67% of solid conversion, when the H₂O and CO₂ ratio was 1 to 1, and WSHV was 186,000 mL/g.h. Activation energy of H₂O spitting and CO₂ splitting was estimated at 87.33 kJ/mol, and 102.85 kJ/mol The pre-exponential factor of H2O splitting and CO2 splitting was 595.24 s^?1 and 698.79 s^?1, respectively.     

Modeling of IT-SOFC with indirect internal reforming operation fueled by methane: Effect of oxygen adding as autothermal reforming

Mathematical models of an Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) with indirect internal reforming operation (IIR-SOFC) fueled by methane were developed. The models were based on a steady-state heterogeneous two-dimensional tubular-design SOFC. The benefit in adding oxygen to methane and steam as the feed for autothermal reforming reaction on the thermal behavior and SOFC performance was simulated. The results indicated that smoother temperature gradient with lower local cooling at the entrance of the reformer channel can be achieved by adding a small amount of oxygen. However, the electrical efficiency noticeably decreased when too high oxygen content was added due to the loss of hydrogen generation from the oxidation reaction; hence, the inlet oxygen to carbon (O/C) molar ratio must be carefully controlled. Another benefit of adding oxygen is the reduction of excess steam requirement, which could reduce the quantity of heat required to generate the steam and eventually increases the overall system performance. It was also found that the operating temperature strongly affects the electrical efficiency achievement and temperature distribution along the SOFC system. By increasing the operating temperature, the system efficiency increases but a significant temperature gradient is also detected. The system with a counter-flow pattern was compared to that with a co-flow pattern. The co-flow pattern provided smoother temperature gradient along the system due to better matching between the heat supplied from the electrochemical reaction and the heat required for the steam reforming reaction. However, the electrical efficiency of the co-flow pattern is lower due to the higher cell polarization at a lower system temperature.     

Investigation of CO2 adsorption by bagasse-based activated carbon

Bagasse-based activated carbon (BAC) and amine-modified BAC were prepared and investigated for CO₂ adsorption capacity. Modifying BAC with amines resulted in a decrease of surface area, but the decreasing magnitude varied depending on type and loading rate of amines. At room temperature, the unmodified BAC was able to adsorb more CO₂ than the amine-modified BAC. This ability was related to the higher surface area of unmodified than that of the modified BAC. When temperature increased, CO₂ adsorption capacity of all absorbents was decreased. However, above 323 K and a concentration of CO₂ lower than 30% v/v, the BAC modified with PEI at 5 and 25 wt% showed higher adsorption capacity. Among all adsorbents under 15% CO₂ and 348 K, BAC-PEI25 showed the highest adsorption capacity (0.20 mmol/g).     

Effect of operating conditions and gas flow patterns on the system performances of IIR-SOFC fueled by methanol

Mathematical models of an indirect internal reforming solid oxide fuel cells (IIR-SOFC) fueled by methanol were developed to analyze the thermal coupling of the internal endothermic steam reforming with exothermic electrochemical reactions and predict the system performance. The simulations indicated that IIR-SOFC fueled by methanol can be well performed as autothermal operation, although slight temperature gradient occurred at the entrance of the reformer chamber. Sensitivity analysis of five important parameters (i.e. operating voltage, reforming catalyst reactivity, inlet steam to carbon ratio, operating pressure and flow direction) was then performed. The increase of operating voltage lowered the average temperature along the reformer chamber and improved the electrical efficiency, but it oppositely reduced the average current density. Greater temperature profile along the system can be obtained by applying the catalyst with lower reforming reactivity; nevertheless, the current density and electrical efficiency slightly decreased. By using high inlet steam to carbon ratio, the cooling spot at the entrance of the reformer can be reduced but both current density and electrical efficiency were decreased. Lastly, with increasing operating pressure, the system efficiency increased and the temperature dropping at the reformer chamber was minimized.     

Preparation of CeO2 Nano Rods Through a Sonication‐Assisted Precipitation

A CeO₂ nanopowder has been synthesized using sonication‐assisted precipitation. The use of ultrasonics during precipitation showed potential morphology control during synthesis. The sonication‐assisted precipitation with highly aqueous base (20 M NaOH) successfully induced the formation of a one‐dimensional nanostructure of CeO₂ rods with a homogeneous shape and size (TEM: 24 nm diameter and 129 nm long). A conventional precipitation under the same conditions provided the CeO₂ in nonuniform sizes and shapes. Heat treatment (1100°C for 4 h) was required for CeO₂ formation when (NH₄)₂C₂O₄ was used instead of NaOH. The concentration of the precipitation agent (15–20 M) strongly affected the size and shape of the product. Importantly, according to the temperature‐programmed reduction/oxidation study, the CeO₂ prepared using the sonication‐assisted route showed a relatively higher level of reversible oxygen storage capacity (2384 μmol/g), compared with the CeO₂ prepared by conventional route (1748 μmol/g).     

Improvement of solid oxide fuel cell performance by using non-uniform potential operation

Theoretical study was carried out to investigate the possible improvement of SOFC performance by using a non-uniform potential operation (SOFC-NUP) in which the operating voltage was allowed to vary along the cell length. Preliminary results of a simple SOFC-NUP with a cell divided into two sections of equal size in term of range of fuel utilization (U_f) indicated that the SOFC-NUP can offer higher power density than an SOFC with uniform potential operation (SOFC-UP) without a reduction of the electrical efficiency. In this work, voltages and section splits were optimized to obtain the maximum power density of the SOFC-NUP. At the optimum splits (S_p,1 = 0.55 and S_p,2 = 0.45), the power density improvement as high as 9.2% could be achieved depending on the level of electrical efficiency. It was further demonstrated that the increase in the number of separated section (n) of the cell could increase the achieved maximum power density but the improvement became less pronounced after n > 3.