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.     

Fixed- and fluidised-bed synthesis of coiled carbon fibres on an in situ generated H2S-modified Ni/Al2O3 catalyst from a NiSO4/Al2O3 precursor

NiSO₄/Al₂O₃ and NiO/Al₂O₃ catalyst precursors were formed by calcination of NiSO₄·6H₂O/Al₂O₃ at 500 and 800 °C, respectively. The catalyst precursor was reduced under H₂ and N₂ and then reacted under C₂H₂, H₂ and N₂ at 650 °C. Coiled carbon fibres were formed in fixed- and fluidised-bed reactors using the NiSO₄/Al₂O₃ catalyst precursor. Thermodynamic modelling using an infinite equilibrium stage construction predicted complete reduction of NiSO₄ to Ni and simultaneous H₂S formation occurs in both fixed- and fluidised-bed systems. XRD measurements confirmed that Ni was the only catalytically active crystalline species present at concentrations >0.5 wt.% (XRD detection limit) post-reduction, however XRF and XPS measurements additionally detected the presence of small quantities (<0.9 wt.% S) of S species. S is adsorbed onto the Ni surfaces during reduction when H₂S is released and dissociates on the Ni surface. Non-coiled carbon fibres produced on the Ni/Al₂O₃ catalyst formed from the NiO/Al₂O₃ precursor demonstrated that modification of Ni/Al₂O₃ with S is required for coiled carbon fibre synthesis.     

Ethanol steam reforming reactions over Al2O3 · SiO2-supported Ni-La catalysts

Nickel-based catalysts supported on Al₂O₃ · SiO₂ were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al₂O₃ · SiO₂ (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al₂O₃ · SiO₂ indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature.     

Catalytic pyrolysis of Athabasca bitumen in H2 atmosphere using microwave irradiation

Microwave-assisted catalytic pyrolysis was carried out for upgrading of Athabasca bitumen. The bitumen can be heated to the desired target temperature (430 °C) for pyrolysis with silicon carbide (SiC), a heating element, in approximately 10 min under microwave irradiation. However, the pyrolysis with SiC only resulted in heavy and viscous liquid product having an API gravity of 17.14°. Addition of Nickel and Molybdenum nanoparticles as catalysts enhanced the pyrolysis performance in terms of liquid yield and quality. In the pyrolysis with Mo nanoparticles, the yield and the API gravity of the liquid product were 72.0 wt% and 20.98°, respectively. However, the separate existence of nanoparticles and SiC in the reactor and the recovery problem of nanoparticles, might limit their application in microwave-assisted pyrolysis. In order to prepare a composite with microwave susceptibility and catalytic activity in one body, transition metals were loaded on alumina coated SiC. When it is compared to the direct application of metal nanoparticles to the pyrolysis of bitumen, the NiMo/Al₂O₃/SiC catalyst showed enhanced catalytic performance. The API gravity and sulfur contents of the liquid products from the pyrolysis with NiMo/Al₂O₃/SiC were 22.42° and 2.84 wt%, respectively.     

Steam reforming of LPG over Ni and Rh supported on Gd-CeO2 and Al2O3: Effect of support and feed composition

The steam reforming of liquefied petroleum gas (LPG) over Ni- and Rh-based catalysts supported on Gd-CeO₂ (CGO) and Al₂O₃ was studied at 750-900 °C. The order of activity was found to be Rh/CGO > Ni/CGO ∼ Rh/Al₂O₃ > Ni/Al₂O₃; we indicated that the comparable activity of Ni/CGO to precious metal Rh/Al₂O₃ is due to the occurring of gas-solid reactions between hydrocarbons and lattice oxygen () on CGO surface along with the reaction taking place on the active site of Ni, which helps preventing the carbon deposition and promoting the steam reforming of LPG.The effects of O₂ (as oxidative steam reforming) and H₂ adding were further studied over Ni/CGO and Ni/Al₂O₃. It was found that the additional of these compounds significantly reduced the amount of carbon deposition and promoted the conversion of hydrocarbons (i.e., LPG as well as CH₄, C₂H₄ and C₂H₆ occurred from the thermal decomposition of LPG) to CO and H₂. Nevertheless, the addition of too high O₂ oppositely decreased H₂ yield due to the oxidizing of Ni particle and the possible combusting of H₂ generated from the reaction, while the addition of too high H₂ also negatively affect the catalyst activity due to the occurring of catalyst active site competition and the inhibition of gas-solid reactions between the gaseous hydrocarbon compounds and on the surface of CGO (for the case of Ni/CGO).     

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.     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

Efficient production of hydrogen and multi-walled carbon nanotubes from ethanol over Fe/Al2O3 catalysts

Fe/Al₂O₃ catalysts with different Fe loadings (10-90 mol%) were prepared by hydrothermal method. Ethanol decomposition was studied over these Fe/Al₂O₃ catalysts at temperatures between 500 and 800 °C to produce hydrogen and multi-walled carbon nanotubes (MWCNTs) at the same time. The results showed that the catalytic activity and stability of Fe/Al₂O₃ depended strongly on the Fe loading and reaction temperature. The Fe(30 mol%)/Al₂O₃ and Fe(40 mol%)/Al₂O₃ were both the effective catalyst for ethanol decomposition into hydrogen and MWCNTs at 600 °C. Several reaction pathways were proposed to explain ethanol decomposition to produce hydrogen and carbon (including nanotube) at the same time.     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

The activity of Rh/Al2O3 and Rh-Na/Al2O3 catalysts for PAHs removal in the waste incineration processes: Effects of particulates, heavy metals, and acid gases

This study investigated the activity of Rh/Al₂O₃ and Rh-Na/Al₂O₃ catalysts for polycyclic aromatic hydrocarbons (PAHs) removal and the influence of particulates, heavy metals, and acid gases (SO₂ and HCl) on the performance of catalysts. The experiments were carried out in a laboratory-scale waste incineration system. Experimental results show that the destruction removal efficiency (DRE) of PAHs by Rh/Al₂O₃ and Rh-Na/Al₂O₃ catalysts were 80% and 59%, respectively when the flue gas did not contain any pollutants. The concentrations of PAHs increased by using a Rh/Al₂O₃ catalyst when the flue gas contained Cd, Pb, and SO₂ and also increased by using a Rh-Na/Al₂O₃ catalyst when the flue gas contained particulates, Cd, and HCl. Adding Na to the Rh/Al₂O₃ catalyst can inhibit the increases of 3-4 ring PAHs when the flue gas contained Pb. The influence of acid gases on the performance of the Rh/Al₂O₃ and Rh-Na/Al₂O₃ catalysts followed the sequence SO₂ > HCl > SO₂ + HCl. The activity of the catalysts for PAHs removal was significantly suppressed by increased concentrations in particulates and Cd, yet promoted by a high Pb concentration. The results of ESCA analysis indicated that the presence of Cd and Pb did not change the chemical states of Rh and Na, but the presence of SO₂ and HCl did.     

Alkali-treatment of ZSM-5 zeolites with different SiO2/Al2O3 ratios and light olefin production by heavy oil cracking

Four kinds of ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios are alkali-treated in 0.2 M NaOH solution for 300 min at 363 K. Changes to the compositions, morphologies, pore sizes, and distributions of the zeolites are compared before and after alkali-treatment. The changes observed are largely influenced by the SiO₂/Al₂O₃ ratios with which the zeolites are synthesized. A possible mechanism of desilication during alkali-treatment is proposed. The SiO₂/Al₂O₃ ratio of zeolites is found to influence the yield of light olefins that use heavy oil as feedstock. Alkali-treated ZSM-5 zeolites produce higher yields of light olefins compared to either untreated zeolites or the industry catalyst CEP-1. It is believed that alkali-treatment introduces mesopores to the zeolites and improves their catalytic cracking ability. ZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 50 also present superior selectivity toward light olefins because of their optimized hierarchical pores.     

The performances of higher alcohol synthesis over nickel modified K2CO3/MoS2 catalyst

Ni modified K₂CO₃/MoS₂ catalyst was prepared and the performance of higher alcohol synthesis catalyst was investigated under the conditions: T = 280–340 °C, H₂/CO (molar radio) = 2.0, GHSV = 3000 h^− 1, and P = 10.0 MPa. Compared with conventional K₂CO₃/MoS₂ catalyst, Ni/K₂CO₃/MoS₂ catalyst showed higher activity and higher selectivity to C₂⁺OH. The optimum temperature range was 320–340 °C and the maximum space-time yield (STY) of alcohol 0.30 g/ml h was obtained at 320 °C. The selectivity to hydrocarbons over Ni/K₂CO₃/MoS₂ was higher, however, it was close to that of K₂CO₃/MoS₂ catalyst as the temperature increased. The results indicated that nickel was an efficient promoter to improve the activity and selectivity of K₂CO₃/MoS₂ catalyst.     

Ethanol reforming and partial oxidation with Cu/Nb2O5 catalyst

Ethanol reforming and partial oxidation were studied on Cu/Nb₂O₅ and Ni/Al₂O₃ catalysts. Compared to the Ni/Al₂O₃ catalyst, the Cu/Nb₂O₅ catalyst presents conversion as high as Ni/Al₂O₃ catalyst, however, for the same level of formation of hydrogen it occurs at much lower temperature on the Cu/Nb₂O₅ catalyst, 200 °C lower than for the Ni/Al₂O₃ catalyst, with remarkable little formation of CO, which can be attributed to the strong interaction between copper and niobia. Temperature-programmed desorption (TPD-ethanol) and surface reactions (TPSR) of partial oxidation of ethanol showed formation of ethylene, acetaldehyde, ethane and mainly H₂ and CO₂ besides little methane. DRIFTS results are in accordance with TPD analysis and the formation of acetate species at room temperature suggests reactivity of the surface and its oxidative dehydrogenation capacity. The adsorption of ethanol gives rise to ethoxide species, which form acetate and acetaldehyde that can be oxidized to CO₂ via carbonate. A comparison with reported results for Cu/Al₂O₃ this catalyst is promising, yielding high level of H₂ with little CO production during reforming and partial oxidation reaction. The maximum H₂ formation for the partial oxidation of ethanol was 41% at ratio (O₂/Et) 0.8, increasing to 50% at ratio 1.5. The H₂/CO is around 10 for the partial oxidation and 7 for steam reforming, which is excellent, compared to the Ni/Al₂O₃ catalyst with a factor 4–8 lower.     

Activity and characterization of Rh/Al2O3 and Rh-Na/Al2O3 catalysts for the SCR of NO with CO in the presence of SO2 and HCl

SO₂ and HCl are major pollutants emitted from waste incineration processes. Both pollutants are difficult to remove completely and can enter the catalytic reactor. In this work, the effects of SO₂ and HCl on the performance of Rh/Al₂O₃ and Rh-Na/Al₂O₃ catalysts for NO removal were investigated in simulated waste incineration conditions. The characterizations of the catalysts were analyzed by BET, SEM/EDS, XRD, and ESCA. Experimental results indicated the 1%Rh/Al₂O₃ catalyst was significantly deactivated for NO and CO conversions when SO₂ and HCl coexisted in the flue gas. The addition of between 2 and 10 wt.% Na promoted the activity of the 1%Rh/Al₂O₃ catalyst for NO removal, but decreased the CO oxidation and BET surface area. The catalytic activity for NO removal was inhibited by HCl as a result of the formation of RhCl₃. Adding Na to the Rh/Al₂O₃ catalyst decreased the inhibition of SO₂ because of the formation of Na₂SO₄, which was observed in the XRD and ESCA analyses. SEM mapping/EDS showed that more S was residual on the surface of the Rh-Na/Al₂O₃ catalyst than Cl.     

Spark plasma sintering technique for reaction sintering of Al2O3/Ni nanocomposite and its mechanical properties

Al₂O₃/Ni nanocomposites were prepared by spark plasma sintering (SPS) using reaction sintering method and the mechanical properties of the obtained nanocomposites are reported. The starting materials of Al₂O₃–NiO solid solution were synthesized from aluminum sulfate and nickel sulfate. These Al₂O₃–NiO powders were changed into Al₂O₃ and Ni phases during sintering process. The obtained nanocomposites showed high relative densities (>98%). SEM micrographs showed homogeneously dispersed Ni grains in the matrix. The 3-point strength and the fracture toughness of the composites significantly improved from 450 MPa in the monolithic α-Al₂O₃ to 766 MPa in the 10 mol% (2.8 vol.%) Ni nanocomposite and from 3.7 to 5.6 MPa m^1/2 in 13 mol% (3.7 vol.%) Ni nanocomposite. On the other hand, Young's modulus and Vickers hardness of the nanocomposites were mostly same as those of the monolithic α-Al₂O₃.     

Effects of Al2O3 addition on the sintering behavior and microwave dielectric properties of CaSiO3 ceramics

The effects of Al₂O₃ addition on the densification, structure and microwave dielectric properties of CaSiO₃ ceramics have been investigated. The Al₂O₃ addition results in the presence of two distinct phases, e.g. Ca₂Al₂SiO₇ and CaAl₂Si₂O₈, which can restrict the growth of CaSiO₃ grains by surrounding their boundaries and also improve the bulk density of CaSiO₃-Al₂O₃ ceramics. However, excessive addition (≥2 wt%) of Al₂O₃ undermines the microwave dielectric properties of the title ceramics since the derived phases of Ca₂Al₂SiO₇ and CaAl₂Si₂O₈ have poor quality factor. The optimum amount of Al₂O₃ addition is found to be 1 wt%, and the derived CaSiO₃-Al₂O₃ ceramic sintered at 1250 °C presents improved microwave dielectric properties of ?_r = 6.66 and Q × f = 24,626 GHz, which is much better than those of pure CaSiO₃ ceramic sintered at 1340 °C (Q × f = 13,109 GHz).     

Preparation of Cu/ZnO/Al2O3 catalyst under microwave irradiation for slurry methanol synthesis

Cu/ZnO/Al₂O₃ catalysts with Cu/Zn/Al ratios of 6/3/1 were precipitated and aged by conventional and microwave heating methods and tested in the slurry phase reactor for methanol synthesis. The effect of technological condition of precipitation and aging process under microwave irradiation on the catalytic performance was investigated to optimize the preparing condition of Cu/ZnO/Al₂O₃ catalyst. The results showed that the microwave irradiation during precipitation process could improve the activity of the catalyst, but had little effect on the stability. While the microwave irradiation during aging process has a great benefit to both the activity and stability of the catalyst, the catalyst aged at 80°C for 1 h under microwave irradiation possessed higher methanol space time yield (STY) and more stable catalytic activity. The activity and stability of the catalyst was further enhanced when microwave irradiation was used in both precipitation and aging processes; the optimized condition for the catalyst precursor preparation was precipitation at 60°C and aging at 80°C under microwave irradiation.     

Effects of a Pt/Ce0.68Zr0.32O2 catalyst and NO2 on the kinetics of diesel soot oxidation from thermogravimetric analyses

In this study, the reactivity of well-characterized diesel soot samples is investigated by thermogravimetry under different kinds of oxidizing atmospheres (20% O₂ or 10% O₂ + 700 ppm NO₂) either under catalyzed or non-catalyzed conditions. Whatever the atmosphere used, the catalyst Pt/ceria-zirconia was able to lower significantly the ignition temperature of soot, but the catalytic effect was found to be more pronounced when the oxidation process was assisted by NOx. This is due mainly to the efficiency of both catalyst components (the noble metal and the OSC material) in recycling the NO released after attack of the soot by NO₂. By contrast, the NO₂ is of very limited use in the absence of catalyst under our experimental conditions. The global kinetic parameters representative of the carbonaceous matrix oxidation are determined using a methodological approach combining thermogravimetric experiments and non-linear multivariate regression. The kinetic parameters obtained are consistent both with the literature results and the postulated mechanistic pathways for soot oxidation assisted or not by NOx.     

Pulsed electric current sintering of transparent Cr-doped Al2O3

Pulsed electric current sintering (PECS) was applied to obtain transparent ruby polycrystals. Al₂O₃-Cr₂O₃ powder mixture was prepared by drying an aqueous slurry consisting of Al₂O₃ and Cr(NO₃)₃ followed by PECS consolidation in vacuum at a sintering temperatures ranging from 1100 to 1300 °C with various heating rates between 2 and 100 °C/min and under an applied pressures from 40 to 100 MPa. Slow heating rate and high-pressure lead to highly densified and transparent Cr-doped Al₂O₃ polycrystals at sintering temperature of 1200 °C.     

Characterization of aerogel Ni/Al2O3 catalysts and investigation on their stability for CH4-CO2 reforming in a fluidized bed

The CH₄-CO₂ reforming was investigated in a fluidized bed reactor using nano-sized aerogel Ni/Al₂O₃ catalysts, which were prepared via a sol–gel method combined with a supercritical drying process. The catalysts were characterized with BET, XRD, H₂-TPR and H₂-TPD techniques. Compared with the impregnation catalyst, aerogel catalysts exhibited higher specific surface areas, lower bulk density, smaller Ni particle sizes, stronger metal-support interaction and higher Ni dispersion degrees. All tested aerogel catalysts showed better catalytic activities and stability than the impregnation catalyst. Their catalytic stability tested during 48 h reforming was dependent on their Ni loadings. Characterizations of spent catalysts indicated that only limited graphitic carbon formed on the aerogel catalyst, while massive graphitic carbon with filamentous morphology was observed for the impregnation catalyst, leading to significant catalytic activity degradation. An aerogel catalyst containing 10% Ni showed the best catalytic stability and the lowest rate of carbon deposition among the aerogel catalysts due to its small Ni particle size and strong metal-support interaction.