Catalytic effects of NaOH and ZrO2 for partial oxidative gasification of n-hexadecane and lignin in supercritical water☆

Partial oxidative gasification of n-hexadecane (n-C₁₆) and organosolv-lignin (lignin) was studied by use of a batch type reactor in supercritical water: 673 K, 0.52 cm⁻³ of water density (40 MPa of water pressure at 673 K), and 0.3 of O/C ratio for the n-C₁₆ experiments; 673 K, 0.35 cm⁻³ of water density (30 MPa of water pressure at 673 K), and 1.0 of O/C ratio for the lignin experiments. The experiments without O₂ were also conducted for lignin (lignin decomposition). For all the cases (n-C₁₆ partial oxidation, lignin decomposition, lignin partial oxidation), NaOH or zirconia (ZrO₂) was added in the system as catalysts. Through n-C₁₆ studies, the catalytic effect of NaOH and ZrO₂ on partial oxidation in supercritical water were examined. In the case of lignin partial oxidation, we studied the possibility of partial oxidation in supercritical water for gasification technique of wastes. The yield of H₂ from n-C₁₆ and lignin with zirconia was twice as same as that without catalyst at the same condition. The H₂ yield with NaOH was 4 times higher than that without catalyst. Thus, a base catalyst has a positive effect on partial oxidation of n-C₁₆ and lignin to produce H₂. The catalytic effect of NaOH and ZrO₂ was found to be enhancement of decomposition of intermediate (aldehyde and ketone) into CO, through n-C₁₆ studies. In the case of lignin studies, the enhancement of decomposition of the carbonyl compounds by catalytic effect of NaOH and ZrO₂ inhibit char formation and promotes CO and thus H₂ formation.     

Production of synthesis gas by autothermal reforming of iso-octane and toluene over metal modified Ni-based catalyst

The reforming process of gasoline is an attractive technique for fuel processor or hydrogen station applications. We investigated catalytic autothermal reforming (ATR) of iso-octane and toluene over transition metal supported catalysts. The catalysts were prepared by an incipient wetness impregnation method and characterized by N₂ physisorption, XRD, and TEM techniques before and after the reaction. Many of the tested catalysts displayed reasonably good activity towards the reforming reactions of iso-octane. Especially, Ni/Fe/MgO/Al₂O₃ catalyst showed more activity than the other catalysts tested in this study including commercial HT catalyst. Ni/Fe/MgO/Al₂O₃ catalyst showed good stability for 700 h in the ATR of iso-octane. No major change was observed in catalytic activity in ATR of iso-octane or in the structure of catalyst. Since iso-octane, toluene are surrogates of gasoline, Ni/Fe/MgO/Al₂O₃ catalyst can be considered as ATR catalyst for gasoline fuel processor and hydrogen station systems.     

Performance of a slurry bubble column reactor for Fischer-Tropsch synthesis: Determination of optimum condition

The CO conversion and selectivity to C₁+ and C₁₁+ wax products over Co/Al₂O₃ as well as Ru/Co/Al₂O₃ Fischer-Tropsch (F-T)catalysts were investigated by varying reaction temperature (210-250 °C), system pressure (1.0-3.0 MPa), GHSV (1000-6000 L/kg/h), superficial gas velocity (1.7-13.6 cm/s) and slurry concentration (9.09-26.67 wt.%) in a slurry bubble column reactor (0.05 m diameter × 1.5 m height) to determine the optimum operating conditions. Squalane or paraffin wax was used as initial liquid media. The overall CO conversion increased with increasing reaction temperature, system pressure and catalyst concentration. However, the local maximum CO conversion was exhibited at GHSV of 1500-2000 L/kg/h and superficial gas velocity of 3.4-5.0 cm/s. The CO conversion in the case of Ru/Co/Al₂O₃ was much higher and stable than that in the case of Co/Al₂O₃. The selectivity to C₁₁+ wax products increased slightly with increasing GHSV; on the other hand, it decreased with increasing reaction temperature, system pressure, and solid concentration in a slurry bubble column reactor. It could be concluded that the optimum operating conditions based on the yield of hydrocarbons and wax products were; U_G = 6.8-10 cm/s, Cs = 15 wt.%, T = 220-230 °C, P = 2.0 MPa in a slurry bubble column reactor for F-T synthesis.     

Mixtures of carbon and Ni/Al2O3 as catalysts for the microwave-assisted CO2 reforming of CH4

In this work, the microwave-assisted CO₂ reforming of CH₄ over mixtures of carbonaceous materials and an in-lab prepared Ni/Al₂O₃ was studied. Ni/Al₂O₃ is not heated by microwave radiation, and for this reason, microwave receptors, such as carbonaceous materials, must be mixed with this catalyst. In order to evaluate the role of the carbonaceous component of the blend, two different carbonaceous materials were used: an activated carbon, FY5, and a metallurgical coke, CQ. The carbonaceous component acted not only as microwave receptor but also as catalyst and, consequently, it influenced the catalytic activity of the mixture. FY5 + Ni/Al₂O₃ was found to be a better catalyst than CQ + Ni/Al₂O₃, since FY5 on its own showed a better catalytic activity than CQ. Ni/FY5, which consists of Ni impregnated directly onto the microwave receptor, was also evaluated as a catalyst. It was found that the catalytic activity of the mixture FY5 + Ni/Al₂O₃ was better than that of Ni/FY5. Finally, the influence of the heating device on the catalytic activity of FY5 + Ni/Al₂O₃ was studied. Conversions over FY5 + Ni/Al₂O₃ and microwave heating were found to be similar to conversions over Ni/Al₂O₃ and conventional heating.     

Influence of preparation parameters on catalytic performance of samaria in isosynthesis

Isosynthesis is referred to the reaction that selectively converts syn-gas (CO + H₂) to i-C₄ hydrocarbons. Sm₂O₃ catalysts were prepared using a sol–gel technique with changing preparing parameters and the structure and textural properties of the catalysts were characterized by N₂ adsorption–desorption isotherm, XRD and TEM. The influences of preparation parameters on the physical properties and the catalytic performance of Sm₂O₃ in isosynthesis were studied. The results showed that the Sm₂O₃ catalysts had lower activity but higher iso-C₄ selectivity in the CO hydrogenation, compared with ZrO₂ catalysts. Different preparation parameters had effects on the catalytic performance of Sm₂O₃ in isosynthesis. The Sm₂O₃ catalysts prepared by alco-method with highest surface area had the highest activity for iso-C₄ formation.     

Hydroisomerization of n-hexane and n-heptane over platinum-promoted Cs2.5H0.5PW12O40 (Cs2.5) studied in comparison with several other solid acids

Isomerization of n-hexane and n-heptane was carried out over Cs_2.5H_0.5PW₁₂O₄₀ (denoted by Cs2.5) promoted by Pt which was introduced by either impregnation of H₂PtCl₆ or mechanical mixing of Pt/Al₂O₃ and over non-promoted Cs_2.5H_0.5PW₁₂O₄₀ in the presence of hydrogen at atmospheric pressure. The reaction temperature studied was relatively low (typically 453 and 423 K for n-hexane and n-heptane, respectively) and the hydrogen pressure was also rather low (standard conditions: feed = n-alkane 0.05 atm, H₂ 0.20 atm, N₂ balance; W/F = 40 g h mol⁻¹). Results were compared with those obtained under the same conditions for other Pt-promoted solid acids, where particular attention was paid to the time courses of the reaction (initial vs. stationary performance). Both the activity and selectivity of Cs2.5 at the initial stage (after 5 min) increased by the addition of the Pt component. Pressure dependencies of the rate at the initial stage were approximately first and −0.5th orders in alkane and hydrogen, respectively. Most remarkable was the suppression of the deactivation during the reaction in the presence of both Pt and hydrogen. For example, the mechanical mixture of Pt/Al₂O₃ and Cs2.5 (abbreviated as Pt+Cs2.5) showed little deactivation and much improved selectivity; resulting in high stationary conversion and selectivity; e.g., 98.4 and 92.1% selectivities for n-hexane and n-heptane at the conversions of 58.6 and 39.4%, respectively. Most of the results were well explained by a classical bifunctional mechanism, although other mechanisms are not all excluded. As for the other solid acids, the initial activity of Pt-promoted SO₄/ZrO₂ was high, but decreased rapidly. The deactivation was small with Pt-promoted H-ZSM-5, but the activity was low. The stationary yields of isomerized products were higher for Pt-promoted beta zeolite and Al-pillared saponite (tested only for n-heptane), although higher reaction temperatures were necessary. This revised version was published online in August 2006 with corrections to the Cover Date.     

Oxidative desulfurization of Gas oil by polyoxometalates catalysts

Several polyoxometalates: Na₂HPM₁₂O₄₀, H₃PM₁₂O₄₀, Na₂HPM₁₂O₄₀, (VO)H[PM₁₂O₄₀] and (n-Bu₄N)₃[PM₁₂O₄₀] (M = Mo and W) as well as (n-Bu₄N)_3 + x[PW_12−xV_xO₄₀] (x = 0–3) were synthesized and characterized. Benzothiophene, dibenzothiophene and 4,6-dimethyl-dibenzothiophene were used as model sulfur compounds in gas oil. The oxidation reaction was performed using different polyoxometalates as catalyst and H₂O₂/acetic acid. The experimental results show that the W-based polyoxometalate catalysts are more active than the Mo catalysts. The oxidation reactivity of the catalysts depends on the type of countercation: Na⁺ > H⁺ > (VO)⁺ > (n-Bu₄N)⁺. In a series of (n-Bu₄N)_3 + x [PW_12−xV_xO₄₀] (x = 0–3) the order of catalytic activity is V₃ > V₂ > V₁ > V₀. The reactivity order of the sulfur compounds is: dibenzothiophene > 4,6-dimethyldibenzo-thiophene > benzothiophene. The catalytic system in this work was used for the oxidation of gas oil combined with solvent extraction to remove sulfur content in gas oil. Under mild reaction condition, high sulfur removal up to 98% can be achieved with high oil recovery (90%).     

Catalytic Hydroprocessing of p-Cresol: Metal, Solvent and Mass-Transfer Effects

A systematic study of the comparative performances of supported Pt, Pd, Ru and conventional CoMo/Al₂O₃, NiMo/Al₂O₃, NiW/Al₂O₃ catalysts as well as the effects of solvent, H₂ pressure and temperature on the hydroprocessing activity of a representative model bio-oil compound (e.g., p-cresol) is presented. With water as solvent, Pt/C catalyst shows the highest activity and selectivity towards hydrocarbons (toluene and methylcyclohexane), followed by Pt/Al₂O₃, Pd and Ru catalysts. Calculations indicate that the reactions in aqueous phase are hindered by mass-transfer limitations at the investigated conditions. In contrast, with supercritical n-heptane as solvent at identical pressure and temperature, the reactant and H₂ are completely miscible and calculations indicate that mass-transfer limitations are eliminated. All the noble metal catalysts (Pt, Pd and Ru) show nearly total conversion but low selectivity to toluene in supercritical n-heptane. Further, conventional CoMo/Al₂O₃, NiMo/Al₂O₃ and NiW/Al₂O₃ catalysts do not show any hydrodeoxygenation activity in water, but in supercritical n-heptane, CoMo/Al₂O₃ shows the highest activity among the tested conventional catalysts with 97?% selectivity to toluene. Systematic parametric investigations with Pt/C and Pt/Al₂O₃ catalysts indicate that with water as the solvent, the reaction occurs in a liquid phase with low H₂ availability (i.e., low H₂ surface coverage) and toluene formation is favored. In supercritical n-heptane with high H₂ availability (i.e., high H₂ surface coverage), the ring hydrogenation pathway is favored leading to the high selectivity to 4-methylcyclohexanol. In addition to differences in H₂ surface coverage, the starkly different selectivities between the two solvents may also be due to the influence of solvent polarity on p-cresol adsorption characteristics.     

In situ DRIFTS study of the effect of structure (CeO2–La2O3) and surface (Na) modifiers on the catalytic and surface behaviour of Pt/γ-Al2O3 catalyst under simulated exhaust conditions

The nature and relative populations of adsorbed species formed on the surface of un-promoted and sodium-promoted Pt catalysts supported either on bare Al₂O₃ or CeO₂/La₂O₃-modified Al₂O₃, were investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under simulated automobile exhaust conditions (CO + NO + C₃H₆ + O₂) at the stoichiometric point. The DRIFT spectra indicate that interaction of the reaction mixture with the Pt/Al₂O₃ catalyst leads mainly to formation of formates and acetates on the support and carbonyl species on partially positively charged Pt atoms (Pt^δ+). Although enrichment of Al₂O₃ with lanthanide elements (CeO₂ and La₂O₃) does not significantly modify the carboxylate species formed on the support, it causes significant modification of the oxidation state of Pt, as indicated by the appearance of a substantial population of carbonyl species on reduced Pt sites (Pt⁰–CO). This modification of the Pt component is enhanced when Na-promotion is used, leading to formation of carbonyl species only on electron enriched Pt (i.e., fully reduced Pt⁰ sites) and to the formation of NCO on these Pt entities (2180 cm⁻¹). The latter are thought to result from enhanced NO dissociation at Na-modified Pt sites. These results correlate well with observed differences in the catalytic performance of the three different systems.     

The promotional effect of Cr on catalytic activity of Pt/ZSM-35 for H2-SCR in excess oxygen

Selective catalytic reduction of NO by hydrogen was studied over Cr modified Pt/ZSM-35 catalysts. The preparation process greatly influenced catalytic activity and sample prepared by co-impregnation method exhibits the best activity. In situ DRIFT studies revealed that on Pt–Cr/ZSM-35, (1) new Pt-NO^δ+ and NO species adsorbed on Pt were detected upon NO + O₂ adsorption; (2) much more ammonia species were formed under reaction condition. Cr addition not only enhanced the adsorption of NO_x but also promoted the formation of surface NH₄⁺ species, which should be the origin of promotional effect of Cr on Pt/ZSM-35 for H₂-SCR reaction.     

Raising Co/Al2O3 catalyst lifetime in Fischer–Tropsch synthesis by using a novel dual-bed reactor

Accelerated deactivation of 15 wt.% Co/Al₂O₃ catalyst in Fischer–Tropsch synthesis (FTS) in a single-bed and a dual-bed reactor is reported. Water was found to have a remarkable effect on the deactivation of Co/Al₂O₃ catalyst during FTS. Synthesis at higher temperatures and lower space velocities resulted in higher values of P_H2O/(P_CO + P_H2) and P_H2O/P_CO and higher catalyst deactivation rates. Water-induced back-oxidation of cobalt, cobalt–alumina interactions, irreducible cobalt aluminates formation and refractory coke formation are the main sources of deactivation. When the water to carbon monoxide plus hydrogen ratio P_H2O/(P_CO + P_H2) is greater than about 0.55 or water to carbon monoxide ratio P_H2O/P_CO is greater than about 1.5, it is not uncommon to find rapid catalyst deactivation. Separation of water and heavy hydrocarbons between the two catalytic beds of the dual-bed reactor, resulted in 62% lower catalyst deactivation rate than that of the single-bed reactor. The amount of refractory coke formation on the catalysts of the dual-bed reactor is 34% lower than that of the single-bed reactor. It was revealed that activity recovery of the used catalysts of the dual-bed is higher than that of the single-bed reactor.     

n-octane dehydrocyclisation on monofunctional and bifunctional Pt/Al2O3 catalyst

The dehydrocyclisation of n-octane to iso-octane, ethylbenzene and o-, m- and p-xylene was investigated on monofunctional (non-acidic) and bifunctional (acidic) Pt/Al₂O₃ catalyst in a microcatalytic reactor with hydrogen as carrier at 1.8 atm and 563–673 K. On bifunctional Pt/Al₂O₃, the total conversion of n-octane started from a high value and decreased with increasing temperature for all pulse sizes investigated. The primary product of n-octane conversion on acidic Pt/Al₂O₃ was iso-octane. The product yield-temperature profiles showed a large initial production of iso-octane which decreased to a minimum as the catalyst temperature increased due to its conversion to ethylbenzene and o-xylene. On non-acidic Pt/Al₂O₃, the total conversion of n-octane increased initially and then went through a maximum as the catalyst temperature increased. The primary products of the reaction were found to be ethylbenzene and o-xylene, indicative of the activity of the metal to effect these ring closure reactions.     

CoAl2O4 spinel catalyst for soot combustion with NOx/O2

Mesoporous and nanosized cobalt aluminate spinel with high specific surface area was prepared using microwave assisted glycothermal method and used as soot combustion catalyst in a NO_x + O₂ stream. For comparison, zinc aluminate spinel and alumina supported platinum catalysts were prepared and tested. All samples were characterised using XRD, (HR)TEM, N₂ adsorption–desorption measurements. The CoAl₂O₄ spinel was able to oxidise soot as fast as the reference Pt/Al₂O₃ catalyst. Its catalytic activity can be attributed to a high NO_x chemisorption on the surface of this spinel, which leads to the fast oxidation of NO to NO₂.     

Electro-catalytic oxidation of CO on Pt catalyst supported on carbon nanotubes pretreated with oxidative acids

Characteristics of nanosized Pt electro-catalyst deposited on carbon nanotubes (CNTs) were studied with CO-stripping voltammogram and chronoamperometry measurements. The CNTs were pretreated by oxidation in HNO₃, mixed HNO₃ + H₂SO₄ and H₂SO₄ + K₂Cr₂O₇ solution, respectively, to enable surface modification. Well-homogenized Pt particles (average size: ≈3 nm) were loaded onto the pretreated CNT samples by a modified colloidal method. TEM, BET, FTIR and XRD techniques were used to characterize the physicochemical properties of the pretreated CNT samples. In the electro-oxidation of CO, all the Pt/CNT samples showed lower on-set as well as peak potentials than the conventional Pt/XC-72 electro-catalyst, indicating that the Pt/CNT samples were more resistant to CO poisoning and could be superior anode electro-catalyst for the proton exchange membrane fuel cells (PEMFCs). Moreover, we found that the pretreatment of CNTs in mixed HNO₃ + H₂SO₄ solution was very beneficial for the performance enhancement of Pt/CNT electro-catalyst; the catalyst obtained as such gave the lowest peak potential and the highest catalytic activity for the electro-oxidation of CO. Larger amount of oxygen-containing functional groups, higher percentage of mesopores, and higher graphitic crystallinity of the pretreated CNTs were considered crucial for the performance enhancement, e.g., by strengthening the interaction between Pt nanoparticles and the CNT support and enhancing the mass diffusion in the electro-chemical reaction.     

Pure and mixed gas CH4 and n-C4H10 sorption and dilation in poly(1-trimethylsilyl-1-propyne)

Pure and mixed gas n-C₄H₁₀ and CH₄ sorption and dilation in poly(1-trimethylsilyl-1-propyne) (PTMSP) are reported at temperatures ranging from −20 to 35 °C. The presence of n-C₄H₁₀ in the mixture considerably reduces CH₄ solubility. For example, CH₄ solubility (in the limit of zero CH₄ fugacity) at 25°C decreases from 4.0 (pure gas) to 0.78 cm³(STP)/(cm³ polymer atm) in the presence of n-C₄H₁₀ at an activity of 0.60. At −20 °C, CH₄ solubility decreases by almost an order of magnitude, from 10.2 (pure gas) to 1.22 cm³(STP)/(cm³ polymer atm) in the presence of n-C₄H₁₀ at an activity of 0.61. In contrast, n-C₄H₁₀ mixture sorption properties are not measurably affected by the presence of CH₄. The dual mode sorption model parameters for CH₄ and n-C₄H₁₀ in PTMSP were determined from pure and mixed gas sorption measurements, and this model can adequately describe the sorption data. The n-C₄H₁₀/CH₄ mixed gas solubility selectivity in PTMSP decreases as temperature increases and as n-C₄H₁₀ activity increases. For example, at 25 °C, the n-C₄H₁₀/CH₄ solubility selectivity decreases from 250 to 120 as n-C₄H₁₀ activity increases from 0.02 to 0.25. At −20 °C and an n-C₄H₁₀ activity of 0.24, the n-C₄H₁₀/CH₄ solubility selectivity is 590. Penetrant-induced volume dilation of PTMSP can be adequately modeled by assuming that all swelling is caused by penetrant molecules sorbed in the polymer's dense equilibrium region (i.e., the Henry's law region) during sorption. However, the best fit partial molar volumes in the Henry's law region for the dilation data are considerably lower than the penetrant partial molar volumes in liquids, suggesting that further theoretical efforts are needed to develop predictive models of volume dilation in high free volume glassy polymers.     

Pt/BEA–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for the isomerization of benzene/heptane mixtures. I: Optimizing the support’s composition

Pt/BEA–Al₂O₃ catalysts for the hydroisomerization of benzene-containing gasoline fractions are studied using a model feedstock (20% benzene and 80% n-heptane). The catalysts are prepared by varying the zeolite content from 5 to 70 wt % at a constant Pt loading of 0.3 wt % in all samples, with an aqueous H₂PtCl₆ solution being used as the Pt precursor. The acid properties of the samples are studied by means of temperature-programmed desorption (TPD). The effect of the support’s zeolite/binder ratio on the activity of the catalysts is determined: an increase in the zeolite content raises the system’s acidity and shifts the range of the reaction toward lower temperatures. The optimum zeolite/binder ratio is found to be 30% BEA/70% Al₂O₃. Changing the SiO₂/Al₂O₃ ratio of the zeolite from 25 to 40 is shown to have no noticeable effect on catalyst activity. The use of the catalysts supported on 30% BEA/70% Al₂O₃ in the hydroisomerization of benzenecontaining gasoline fractions can be recommended for improving environmental performance.     

Studying the role of the state of platinum in Pt/SO4/ZrO2/Al2O3 catalysts in the isomerization of n-hexane

Samples of SO₄/ZrO₂/Al₂O₃ and Pt/Al₂O₃ Pt/Al₂O₃ catalysts and their physical mixtures are prepared, and the catalytic properties of the samples in n-hexane isomerization are studied. The considerable effect of the state of platinum on the catalytic performance of the samples is revealed. IR spectroscopy (CO_ads), oxygen chemisorption, and oxygen-hydrogen titration show that the reduced catalysts contain ionic forms of platinum capable of adsorbing up to three hydrogen atoms per each surface atom of platinum. By means of H/D isotopic exchange, it is found that specific properties of ionic platinum are apparent in the formation of the hydride form of adsorbed hydrogen. It is speculated that the activity and stability of catalysts based on sulfated zirconia in n-hexane isomerization can be attributed to the involvement of ionic and metallic platinum in the activation of hydrogen. The results can be used to develop effective catalysts for the isomerization of C₅–C₆ gasoline fractions in order to obtain the isomerizate as a high-octane additive for modern gasolines.     

The effects of Pt promotion on the oxi-reduction properties of alumina supported nickel catalysts for oxidative steam-reforming of methane: Temperature-resolved XAFS analysis

The effects of Pt trace addition on the oxi-reduction properties of the Ni/Al₂O₃ and Ni/La–Al₂O₃ catalysts during partial oxidation of methane (POM) and autothermal reforming of methane (ATR) were investigated. The xPt–Ni/yLa–Al₂O₃ catalysts containing 15 wt% of Ni, 0 or 12 wt% of La and 0 or 0.05 wt% of Pt were characterized by temperature-resolved X-ray absorption near edge structure (XANES) spectroscopy under various atmospheres.The in situ XANES analysis for Pt–Ni/Al₂O₃ under H₂ and CO revealed that the presence of Pt sites can initiate the NiO reduction process by rapid dissociation of H₂ and migration of atomic H to the NiO surface by hydrogen spillover. On the other hand, in situ XANES analysis under CH₄ showed that the presence of Pt sites induces the activation of the methane, probably by initial dissociation of methane (CH₄ → CH₃ + H) followed by migration of atomic H to the NiO surface. In situ XANES experiments under a POM mixture demonstrate that Pt has an important role keeping Ni in the metallic state. The catalytic test results for POM and ATR demonstrate that Pt is an important promoter to maintain Ni in the metallic state at the inlet region of the catalytic bed, where CH₄ and O₂ coexist.     

Catalytic steam reforming of ethane and propane over CeO2-doped Ni/Al2O3 at SOFC temperature: Improvement of resistance toward carbon formation by the redox property of doping CeO2

Ni/Al₂O₃ with the doping of CeO₂ was found to have useful activity to reform ethane and propane with steam under Solid Oxide Fuel Cells (SOFCs) conditions, 700-900 °C. CeO₂-doped Ni/Al₂O₃ with 14% ceria doping content showed the best reforming activity among those with the ceria content between 0 and 20%. The amount of carbon formation decreased with increasing Ce content. However, Ni was easily oxidized when more than 16% of ceria was doped. Compared to conventional Ni/Al₂O₃, 14%CeO₂-doped Ni/Al₂O₃ provides significantly higher reforming reactivity and resistance toward carbon deposition. These enhancements are mainly due to the influence of the redox properties of doped ceria. Regarding the temperature programmed reduction experiments (TPR-1), the redox properties and the oxygen storage capacity (OSC) for the catalysts increased with increasing Ce doping content. In addition, it was also proven in the present work that the redox of these catalysts are reversible, according to the temperature programmed oxidation (TPO) and the second time temperature programmed reduction (TPR-2) results.During the reforming process, in addition to the reactions on Ni surface, the gas-solid reactions between the gaseous components presented in the system (C₂H₆, C₃H₈, C₂H₄, CH₄, CO₂, CO, H₂O, and H₂) and the lattice oxygen (O_x) on ceria surface also take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen (O_x) on ceria surface (C_nH_m+O_x→nCO+m/2(H₂)+O_x−n) can prevent the formation of carbon species on Ni surface from hydrocarbons decomposition reaction (C_nH_m⇔nC+m/2H₂). Moreover, the formation of carbon via Boudard reaction (2CO⇔CO₂+C) is also reduced by the gas-solid reaction of carbon monoxide (produced from steam reforming) with the lattice oxygen (CO+O_x⇔CO₂+O_x−1).     

Comparative study of Li[Co1−zAlz]O2 prepared by solid-state and co-precipitation methods

Li[Co_1−zAl_z]O₂ (0 ≤ z ≤ 0.5) samples were prepared by co-precipitation and solid-state methods. The lattice constants varied smoothly with z for the co-precipitated samples but deviated for the solid-state samples above z = 0.2. The solid-state method may not produce materials with a uniform cation distribution when the aluminum content is large or when the duration of heating is too brief. Non-stoichiometric Li_x[Co_0.9Al_0.1]O₂ samples were synthesized by the co-precipitation method at various nominal compositions x = Li/(Co + Al) = 0.95, 1.0, 1.1, 1.2, 1.3. XRD patterns of the Li_x[Co_0.9Al_0.1]O₂ samples suggest the solid solution limit is between Li/(Co + Al) = 1.1 and 1.2. Electrochemical studies of the Li[Co_1−zAl_z]O₂ samples were used to measure the rate of capacity reduction with Al content, found to be about −250 ± 30 (mAh/g)/(z = 1). Literature work on Li[Ni_1/3Mn_1/3Co_1/3−zAl_z]O₂, Li[Ni_1−zAl_z]O₂ and Li[Mn_2−yAl_y]O₄ demonstrates the same rate of capacity reduction with Al/(Al + M) ratio. These studies serve as baseline characterization of samples to be used to determine the impact of Al content on the thermal stability of delithiated Li[Co_1−zAl_z]O₂ in electrolyte.