The relation between morphology of (Co)MoS2 phases and selective hydrodesulfurization for CoMo catalysts

A series of CoMo catalysts were prepared by various methods with three different supports (Al₂O₃-1 of γ phase, Al₂O₃-2 containing γ and δ mixed phases, SiO₂). And the effect of morphology of (Co)MoS₂ phases on selective hydrodesulfurization was studied systematically. The TEM images showed, in general, the average slab length, the stacking number and the ratio of edge/corner of the sulfided catalysts increase remarkably in the order: SiO₂ > Al₂O₃-2 > Al₂O₃-1, with the extent of metal–support interaction decreasing in the order: SiO₂ < Al₂O₃-2 < Al₂O₃-1. And the hydrodesulfurization selectivity correlates linearly with the slab length (or the ratio of edge/corner) of (Co)MoS₂ phases, the longer average slab length, the higher ratio of edge/corner, and then the better hydrodesulfurization selectivity. Among all the catalysts, sulfided CoMo/SiO₂ of the longest average slab length and the highest edge/corner ratio exhibits the best hydrodesulfurization selectivity.     

Catalytic performance of Ag–Co/CeO2 catalyst in NO–CO and NO–CO–O2 system

A new bimetallic catalyst (Ag–Co/CeO₂) was studied for simultaneously catalytic removal of NO and CO in the absence or presence of O₂. CeO₂ prepared by homogeneous precipitation method was optimized as supports for the active components. The addition of Ag on CeO₂ greatly improved the catalytic activities in the lower temperature regions (⩽300 °C), and the introduction of Co on CeO₂ increased the activities at higher temperatures (⩾250 °C). The bimetallic Ag–Co/CeO₂ catalyst combined the advantages of the corresponding individual metal supported catalysts and showed superior activity due to the synergetic effect. The effect of support, temperature, loading amount, GHSV and oxygen on catalysis was investigated. NO and CO could be completely removed in the temperature range of 200–600 °C at a very high space velocity of 120 000 h⁻¹. No deactivation was observed over 4% Ag–0.4% Co/CeO₂ catalyst even after 50 h test.     

The deactivation study of Co–Ru–Zr catalyst depending on supports in the dry reforming of carbon dioxide

Carbon dioxide reforming of methane was performed over Co–Ru–Zr catalyst (0.4 wt% Ru added, calcined at 400 °C) with different supports (SiO₂, γ-Al₂O₃ and MgO) in order to study their deactivation. The Co–Ru–Zr/γ-Al₂O₃ showed the highest activity at first, but severe deactivation was observed due to carbon deposition. Co–Ru–Zr/MgO exhibited low activity because of its low specific surface area. However, the high conversions could be obtained in Co–Ru–Zr/SiO₂, and activity was kept almost constantly for 500 h reaction. The characteristics of the catalysts, before and after the reaction, were investigated employing BET, XRD, TPR, TGA-DTA and TEM.     

Optimising H2 production from model biogas via combined steam reforming and CO shift reactions

H₂ production was studied through steam reforming of a clean model biogas in a fluidized-bed reactor followed by two stages of CO shift reactions (fixed-bed reactors). The steam reforming of biogas was performed over 11.5 wt.% Ni/Al₂O₃ and a molar CH₄/CO₂ ratio of 1.5 was employed as clean model biogas. Excess steam resulted in strong inhibition of carbon formation and an almost complete CH₄ (>98%) conversion was achieved.To optimise H₂ production, CO shift reactions were carried out at high (523–723 K) and low temperatures (423–523 K) using commercial catalysts, based on Cu/Fe/Cr and Cu/Zn, respectively. Increasing steam concentrations led to a lean CO, high H₂ product. The final product compositions following low temperature CO shift reaction (steam to dry gas ratio of 1.5 at 483 K) yielded H₂ at 68% and a CO concentration of 0.2% (equivalent to CO conversion of >99%).     

Promotional effect of SO2 on the activity of Ir/SiO2 for NO reduction with CO under oxygen-rich conditions

The effect of coexisting SO₂ on the activity of silica-supported noble metal catalysts for the selective reduction of NO with CO in the presence of O₂ was investigated. Pt/SiO₂, Rh/SiO₂, and Pd/SiO₂ showed little catalytic activity for NO reduction, irrespective of coexisting SO₂. Although Ir/SiO₂ showed no NO reduction activity in the absence of SO₂, the presence of SO₂ drastically promoted NO reduction. A comparison of the catalytic performance of Ir/SiO₂ and Ir/Al₂O₃ in the presence of SO₂ showed that Ir supported on SiO₂ is more active than Ir on Al₂O₃. SiO₂ was found to be a more effective support than Al₂O₃. The most outstanding feature of the reaction on the Ir/SiO₂ catalyst was that the coexistence of SO₂ and O₂ is essential for NO reduction to occur. The role of coexisting SO₂ was considered to be not only to stabilize but also to create Ir⁰ sites in an oxidizing atmosphere. FT-IR measurements suggested that a cis-type coordinated species of NO and CO on one iridium atom (

) was an intermediate for NO reduction by CO. Although the

species completely disappeared with the addition of O₂ to the reaction gas, the presence of coexisting SO₂ caused a reappearance of the

species. A reaction mechanism in which N₂ and N₂O are produced via the recombination of dissociated N atoms (N_(a) + N_(a) → N₂) and the formation of dimer (NO)₂-type species (2NO → (NO)_2(a) → N₂O + O_(a)), respectively, is proposed.     

Improving the dispersion of CeO2 on γ-Al2O3 to enhance the catalytic performances of CuO/CeO2/γ-Al2O3 catalysts for NO removal by CO

Acetic acid (HAc) aqueous was used as solvent in wetness impregnation to prepare CeO₂-modified γ-Al₂O₃ support. With the help of HAc, the dispersion of CeO₂ on γ-Al₂O₃ is significantly improved and the size of CeO₂ nanoparticles can be controlled through tuning the concentration of HAc aqueous. XPS analysis shows that the percentages of Ce^3 + in CeO₂ nanoparticles will vary with the size. Then we load CuO on the as-prepared CeO₂-modified γ-Al₂O₃ support and choose NO reduction with CO as a probe reaction to investigate the influences of impregnation solvent on the catalytic properties. The results demonstrate that the CuO/CeO₂/γ-Al₂O₃ prepared in the solvent with volume ratio of 20:1 (H₂O:HAc) has the highest activity in NO + CO reaction. Combing the structural characterizations and catalytic performances, we think that the size of the CeO₂ nanoparticles should be a key factor that affects the activities of CuO/CeO₂/γ-Al₂O₃. Furthermore, CuO dispersed on CeO₂ nanoparticles with an average size of ca. 5 nm should be the highest active sites for NO + CO reaction.     

Impact of metal doping on the activity of Au/CeO2 catalysts for catalytic abatement of VOCs and CO in waste gases

The catalytic performance in the total oxidation of CO and methanol over gold catalysts supported on ceria doped by different metal oxides (Me = Fe, Mn and Co) was studied and a strong influence of the nature of dopant was observed. The activity towards the oxidation of CO and CH₃OH was in the order: AuCeCo > AuCe > AuCeFe > AuCeMn. The characterization by XRD and HRTEM evidenced differences in the average size and the distribution of gold particles. AuCeCo catalyst exhibited superior low-temperature CO oxidation activity (100% conversion degree was obtained at 25 °C) and almost 100% total oxidation of CH₃OH at about 40 °C. Higher hydrogen consumption was estimated by means of TPR over this catalyst. The effect of modification with Co₃O₄ of Au/CeO₂ catalysts on their CO oxidation activity was further studied by varying of the dopant content (5, 10 and 15 wt.% Co₃O₄).     

Triton X-100 directed synthesis of mesoporous γ-Al2O3 from coal-series kaolin

Mesoporous γ-Al₂O₃ has been successfully synthesized by using calcined coal-series kaolin as raw material and Triton X-100 (TX-100) as template. The effect of TX-100/Al^3 + ratio on the structural and textural properties of mesoporous γ-Al₂O₃ was investigated. Physical properties of obtained samples were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), thermogravimetric analysis (TG), scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDAX) and Fourier transform infrared spectroscopy (FTIR). The results indicated that the amount of TX-100 influenced the structure and porous properties of mesoporous γ-Al₂O₃ significantly. When TX-100/Al^3 + ratio was in the range of 0.03–0.15, all samples had mesoporous structures with BET surface area of 193.0–261.0 m²/g and pore size of 5.04–6.71 nm. In addition, the reaction mechanism involved in the process was proposed and discussed.     

Direct dehydrogenation of n-butane over Pt/Sn/M/γ-Al2O3 catalysts: Effect of third metal (M) addition

A series of Pt/Sn/M/γ-Al₂O₃ catalysts with different third metal (M = Zn, In, Y, Bi, and Ga) were prepared by a sequential impregnation method for use in the direct dehydrogenation of n-butane to n-butene and 1,3-butadiene. In the direct dehydrogenation of n-butane, Pt/Sn/Zn/γ-Al₂O₃ catalyst showed the best catalytic performance. Catalytic performance decreased in the order of Pt/Sn/Zn/γ-Al₂O₃ > Pt/Sn/In/γ-Al₂O₃ > Pt/Sn/γ-Al₂O₃ > Pt/Sn/Y/γ-Al₂O₃ > Pt/Sn/Bi/γ-Al₂O₃ > Pt/Sn/Ga/γ-Al₂O₃. The catalytic performance increased with increasing metal–support interaction and Pt surface area of the catalyst.     

Catalytic formation of carbonyl sulfide during warm gas clean-up of simulated coal-derived fuel gas with Pd/γ-Al2O3 sorbents

Coal gasification processes, such as the Integrated Gasification Combined Cycle (IGCC), will increase in importance due to the expanding concern over CO₂ emissions and global climate change. During the development of a Pd/γ-Al₂O₃ sorbent for warm (200 °C) fuel gas cleanup, the catalytic formation of carbonyl sulfide (COS), was observed. This is attributed to a heterogeneous reaction involving fuel gas components (CO/CO₂/H₂/H₂S/H₂O) and Pd/γ-Al₂O₃. The concentration of COS increases 200-fold when exposed to the Pd/γ-Al₂O₃ sorbent. A Langmuir–Hinshelwood reaction mechanism is proposed and a kinetic model is developed based on experimental results. The effect of γ-Al₂O₃, a common catalyst for hydrolysis of COS, and H₂O on the COS concentration is discussed.     

Modification of alumina support with TiO2-P25 in CO2 reforming of CH4

Catalyst activity and stability for CO₂ reforming of CH₄ depends specifically upon the support and the active metal. A side reaction of dry reforming of methane is the decomposition to carbon that covers the Ni particles causing catalyst deactivation. Hence, an appropriate combination of Ni with support is needed to allow for long term stable operation. In this paper, CO₂ reforming of CH₄ is studied by investigating the effect of addition of TiO₂-P25 separately to γ-Al₂O₃ and α-Al₂O₃ supports used for nickel based catalyst. The reforming reactions are performed using (CO₂:CH₄) feed ratio of 1:1 and reaction temperature range of 500–800 °C. Both fresh and used catalysts are characterized by SEM and TGA techniques. It is found when α-Al₂O₃ support is modified with 20 wt% TiO₂-P25, the catalyst activity and stability is enhanced. The conversion rates of CH₄ and CO₂ without and with 20 wt% TiO₂-P25, respectively, are changed from 72.3% to 76.7% and 73.3% to 81.2%, respectively, and, most importantly, carbon formation is reduced from 28.1 to 12.8, respectively. However, when γ-Al₂O₃ support is modified with TiO₂-P25, the catalyst activity is enhanced with simultaneous increase in carbon formation.     

Role of ceria in the improvement of SO2 resistance of LaxCe1 − xFeO3 catalysts for catalytic reduction of NO with CO

Perovskite-type catalysts with LaFeO₃ and substituted La_xCe_1 − xFeO₃ compositions were prepared by sol–gel method. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), CO temperature-programmed reduction (CO-TPR), and SO₂ temperature-programmed desorption (SO₂-TPD). Catalytic reaction for NO reduction with CO in the presence of SO₂ has been investigated in this study. LaFeO₃ exhibited an excellent catalytic activity without SO₂, but decreased sharply when SO₂ gas was added to the CO + NO reaction system. In order to inhibit the effect of SO₂, substitution of Ce in the structure of LaFeO₃ perovskite has been investigated. It was found that La_0.6Ce_0.4FeO₃ showed the maximum SO₂ resistance among a series of La_xCe_1 − xFeO3 composite oxides.     

Effect of mixed γ- and χ-crystalline phases in nanocrystalline Al2O3 on the dispersion of cobalt on Al2O3

This paper reports the results of a study into the effect of mixed γ and crystalline phases in Al₂O₃ on the characteristics and catalytic activities for CO hydrogenation of Co/Al₂O₃ catalysts. The catalysts were characterized by X-ray diffraction, N₂ physisorption, transmission electron microscopy, and H₂ chemisorption. Increasing Co loading from 5 to 20 wt% for the mixed phase Al₂O₃-supported Co catalysts resulted in a constant increase in both the number of cobalt metal active sites and the hydrogenation activities. However, for those supported on γ-Al₂O₃, Co dispersion increased up to 15 wt%Co and declined at 20 wt%Co loading. It is suggested that the spherical-shape like morphology of the χ-phase Al₂O₃ prevented agglomeration of Co particles, especially at high Co loadings.     

Preparation and catalytic behavior of second metal Ni supported on a novel conductive structured Cu/γ-Al2O3/Al catalysts through electrolysis on steam reforming of dimethyl ether

Electrochemical treatment was employed to improve the electric conductivity of γ-Al₂O₃/Al. Optimal conditions were found to be 0.5 M KCl solution along with potential of 4 V for 7.5 min. The modified γ-Al₂O₃/Al support showed higher catalytic activity at low temperature because of its bigger specific surface area and more acid amount than γ-Al₂O₃/Al. Moreover, Ni was easily loaded on the modified Cu/γ-Al₂O₃/Al catalyst through electrolysis because of the high electric conductivity. The novel Ni/Cu/γ-Al₂O₃/Al catalyst also exhibited excellent stability for 40 h at 623 K with 100% conversion and 70% H₂ yield in steam reforming of dimethyl ether.     

Preparation of Al2O3–ZrO2 nanocomposite films by laser chemical vapour deposition

Alumina (Al₂O₃)–zirconia (ZrO₂) nanocomposite films were prepared by laser chemical vapour deposition. α-Al₂O₃–ZrO₂ and γ-Al₂O₃–t-ZrO₂ nanocomposite films were prepared at 1207 and 1000 K, respectively. In the nanocomposite films, 10-nm-wide t-ZrO₂ nanodendrites grew inside the α- or γ-Al₂O₃ columnar grains. The γ-Al₂O₃–t-ZrO₂ nanocomposite films exhibited high nanoindentation hardness (28.0 GPa) and heat insulation efficiency (4788 J s^−1/2 m⁻² K⁻¹).     

Identification of the coke accumulation and deactivation sites of Mo2C/HZSM-5 catalyst in CH4 dehydroaromatization

Identifying the preferentially coking sites of Mo₂C/HZSM-5 catalyst in the CH₄ dehydroaromatization at non-oxidative conditions was attempted by employing a physically separable Mo₂C/α-Al₂O₃ + HZSM-5 mixture instead of Mo₂C/HZSM-5 as catalyst. Photographic observation on the spent Mo₂C/α-Al₂O₃ and HZSM-5 components separated from the deactivated mixture and their thermogravimetric analysis clearly revealed that coke accumulation occurred predominantly on the HZSM-5. Then, the comparative activity tests with the physical blends of the deactivated Mo₂C/α-Al₂O₃ + HZSM-5 mixture sample with fresh Mo₂C/α-Al₂O₃ or HZSM-5 further confirmed that the coked HZSM-5 component in the deactivated mixture definitely deactivated while that un-coked Mo₂C constituent remained highly active.     

CO methanation over supported Mo catalysts in the presence of H2S

The effect of various Mo catalyst supports, i.e., γ-Al₂O₃, SiO₂, SiO₂–Al₂O₃, ZrO₂, yttria-stabilized zirconia (YSZ), CeO₂, and TiO₂, on CO hydrogenation in the presence of H₂S was examined. At 5 wt.% Mo loading, Mo/ZrO₂ was determined to be the most active catalyst for this reaction; its activity was dependent on the number of active sites, as determined via NO chemisorption. Raman spectroscopy revealed that MoO₃ transforms into MoS₂ during the reaction.     

The performance of CNT as catalyst support on CO oxidation at low temperature

A carbon nanotube (CNT) was used as catalyst support impregnated with transition metal cobalt for CO oxidation at low temperature. Catalyst properties were analyzed by X-ray powder diffractometer (XRD), X-ray photoelectron spectrometer (XPS), and transmission electron microscope (TEM). Analytical results for TEM and XRD demonstrated that cobalt particles were highly dispersed on the carbon nanotube (20–30 nm) with nanosized cobalt particles (10–15 nm). These investigations indicated that Co/CNT generates about 99% of the high activity for CO conversion at 250 °C and thermally stability that is superior to Co/activated carbon (AC). The optimum reaction conditions for CO conversion were O₂ concentration 3%, operation temperature 250 °C, CO concentration 5000 ppm, and space velocity 156,000 h⁻¹. At 250 °C, CO may act as a reductant for NO reduction over Co/CNT in the presence of oxygen, whereas CO/NO = 2.5 showed that maximum NO reduction was 30%. Under H₂ rich conditions, the optimum reaction temperature for CO conversion was under 300 °C, and performance of CO₂ selectivity was better at 200 °C than 250 °C as the oxygen concentration increased.     

Redispersion effects of citric acid on CoMo/γ-Al2O3 hydrodesulfurization catalysts

Calcined CoMo/γ-Al₂O₃ catalysts were modified by citric acid (CA) with different CA/Co ratios and the corresponding structure evolutions were systematically characterized. Then combined with HDS activity results, potential redispersion effects of CA were suggested: (i) weaken the MoO₃-Al₂O₃ interaction via competitive interacting with the OH groups of alumina surface to realize the redispersion of Mo oxides; (ii) transform tetrahedral MoO₄^2 − or β-CoMoO₄ into octahedral polymolybdate species and promote bulk MoO₃ to form well-dispersed MoO₃; (iii) remove the CoAl₂O₄-like species. These effects probably together promote the resulting sulfided catalysts with more type II CoMoS active sites, thus enhancing the HDS activity.     

Oxidative desulfurization of dibenzothiophene over Fe promoted Co–Mo/Al_2O_3 and Ni–Mo/Al_2O_3 catalysts using hydrogen peroxide and formic acid as oxidants

This work reports the enhancing effect of a highly cost effective and efficient metal, Fe, incorporation to Co or Ni based Mo/Al_2O_3 catalysts in the oxidative desulfurization(ODS) of dibenzothiophene(DBT) using H_2O_2 and formic acid as oxidants. The influence of operating parameters i.e. reaction time, catalyst dose, reaction temperature and oxidant amount on oxidation process was investigated. Results revealed that 99% DBT conversion was achieved at 60 °C and 150 min reaction time over Fe–Ni–Mo/Al_2O_3. Fe tremendously enhanced the ODS activity of Co or Ni based Mo/Al_2O_3 catalysts following the activity order: Fe–Ni–Mo/Al_2O_3 NFe–Co–Mo/Al_2O_3 NNi–Mo/Al_2O_3 NCo–Mo/Al_2O_3, while H_2O_2 exhibited higher oxidation activity than formic acid over all catalyst systems. Insight about the surface morphology and textural properties of fresh and spent catalysts were achieved using scanning electron microscopy(SEM), X-ray diffraction(XRD), energy dispersive X-ray(EDX)analysis, Atomic Absorption Spectroscopy(AAS) and BET surface area analysis, which helped in the interpretation of experimental data. The present study can be deemed as an effective approach on industrial level for ODS of fuel oils crediting to its high efficiency, low process/catalyst cost, safety and mild operating condition.