The state of Tin on Pt–Sn/Nb2O5 catalysts

The effect of tin addition on niobia supported catalysts was studied and compared to the properties of alumina supported bimetallic Pt–Sn catalysts. The catalyst surfaces were probed by methylcyclopentane conversion, showing that both the presence of Sn and the reduction of the support caused a decrease in hydrogenolysis activity, favoring the ring enlargement reaction. The thermodynamics of reduction of these systems, evaluated by following the reduction step (temperature programmed reduction — TPR) with a differential scanning calorimeter (DSC), and irreversible H₂ and CO uptakes, allowed to conclude that a Pt–Sn alloy is formed on niobia supported catalysts.     

CoMo/MgO–Al2O3 supported catalysts: An alternative approach to prepare HDS catalysts

Three different supports were prepared with distinct magnesia–alumina ratio x = MgO/(MgO + Al₂O₃) = 0.01, 0.1 and 0.5. Synthesized supports were impregnated with Co and Mo salts by the incipient wetness method along with 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CyDTA) as chelating agent. Catalysts were characterized by BET surface area, Raman spectroscopy, SEM-EDX and HRTEM (STEM) spectroscopy techniques. The catalysts were evaluated for the thiophene hydrodesulfurization reaction and its activity results are discussed in terms of using chelating agent during the preparation of catalyst. A comparison of the activity between uncalcined and calcined catalysts was made and a higher activity was obtained with calcined MgO–Al₂O₃ supported catalysts. Two different MgO containing calcined catalysts were tested at micro-plant with industrial feedstocks of heavy Maya crude oil. The effect of support composition was observed for hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs) and hydrodenitrogenation (HDN) reactions, which were reported at temperature of 380 °C, pressure of 7 MPa and space-velocity of 1.0 h⁻¹ during 204 h of time-on-stream (TOS).     

Effects of alumina incorporation in coprecipitated NiO–Al2O3 catalysts

The effect of Al₂O₃ levels on the properties of NiO in coprecipitated NiO–Al₂O₃ samples were investigated, using samples with up to 60.7 wt.% Al₂O₃ that had been calcined in the range 300–700°C. Characterization techniques included BET surface area of fresh and reduced catalysts, X-ray diffraction analysis of structure and crystallite size, magnetic susceptibility measurements, oxidizing power, and reducibility in H₂. Only NiO was detected in samples with up to 4.1 wt.% Al₂O₃ for all sample calcination temperatures. Surface areas were similar for all fresh samples but decreased rapidly after calcination at high temperatures. The surface area loss was less for the higher Al₂O₃-containing samples. Nickel oxide crystallite sizes increased at higher calcination temperatures, but remained approximately the same for each Al₂O₃ level.

The NiO was nonstoichiometric (NiO_1+x), with x decreasing at higher calcination temperatures and increasing with small amounts of added Al₂O₃ through a maximum at about 3 wt.% Al₂O₃. However, this did not correlate well with microstrain in the NiO crystallites nor with reducibility, which decreased with Al₂O₃ addition. At higher levels of Al₂O₃ (13.6 wt.% and above), surface areas increased with higher Al₂O₃ loadings, but NiO crystallite sizes remained approximately the same, independent of both Al₂O₃ content and calcination temperature. X-ray diffraction patterns were very diffuse, and it was not possible to rule out the presence of pseudo-spinel combinations of NiO and Al₂O₃. Reducibility was more difficult than with low Al₂O₃ levels, and nonstoichiometry was low and independent of Al₂O₃ content.

Reducibilities of all samples calcined at 300°C correlated well with the final BET surface area of the reduced samples, indicating that more dispersed NiO crystallites are more difficult to reduce, a conclusion that supports a model for reduction proposed previously.     

Ni---Mo/Al2O3 catalysts promoted with phosphorus and fluoride

Ni---Mo/Al₂O₃ catalysts containing two promoters, fluoride and phosphorus, were studied to learn whether the benefits of both promoters could be combined to produce a superior catalyst. Initially, two series of catalysts differing in the sequence of impregnation of the additives were prepared and tested in the hydrocracking of cumene and the hydrodesulfurization of thiophene. Catalysts impregnated in the sequence phosphorus—metals (Ni and Mo)—fluoride were clearly superior to those prepared by adding first phosphorus, then fluoride and finally metals. The more effective series of catalysts was tested in the hydroprocessing of a gas oil feedstock; to determine the resistance of these surfaces to poisoning, tests were also carried out with the same feedstock spiked with quinoline. The bi-promoted catalysts retained fluoride well, and were quite effective in hydrogenation and hydrodesulfurization. They were even more effective than phoshorous-only promoted catalysts in quinoline hydrodenitrogenation.     

Pt–Ba–Al2O3 for NOx storage and reduction: Characterization of the dispersed species

Pt–Ba–Al₂O₃ active and selective for NO_x storage and selective reduction to N₂ has been prepared and tested. Characterization of the parent Al₂O₃, Pt–Al₂O₃ and Ba–Al₂O₃ materials, as well as of Pt–Ba–Al₂O₃ catalyst in the oxidized, reduced and sulphated state has been performed by FT-IR spectroscopy of low-temperature adsorbed carbon monoxide and of adsorbed acetonitrile. XRD, TEM and XPS analyses have also been performed. Evidence for the predominance of Ba species, which are highly dispersed on the alumina support surface, and may be carbonated or sulphated, has been provided. Competitive interaction of Pt and Ba species with the surface sites of alumina has also been found.     

TiO2-coated on Al2O3 support prepared by the CVD method for HDS catalysts

Mo---Co or Mo---Ni catalysts supported on alumina (Al₂O₃) have been widely used for hydrodesulfurization (HDS) of heavy petroleum fractions. In order to enhance the catalytic activities for HDS, a composite type support (TiO₂-Al₂O₃) prepared by the chemical vapor deposition (CVD) method has been studied. We found that Mo catalyst supported on TiO₂-Al₂O₃ showed much higher catalytic activity for HDS of dibenzothiophene derivatives than the catalysts supported on Al₂O₃.     

Catalytic reforming n-octane on Pt–Re/Al2O3 catalysts promoted by different additives

The effect of decationized forms of NaY, NaZSM-5 zeolites on the properties of Pt–Re/Al₂O₃ catalyst at n-octane reforming has been shown. The promoted additives increase the isomerization activity of catalysts. Activity and selectivity of the modified catalysts depend on both degree of ion exchange and (Si/Al) ratio of zeolites. One hundred percent selectivity of i-octane formation is reached at the introduction of promoter additive (element of the V group).     

Synergetic effect of combined use of Cu–ZnO–Al2O3 and Pt–Al2O3 for the steam reforming of methanol

Commercial Cu–ZnO–Al₂O₃ catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al₂O₃ catalyst with Pt–Al₂O₃ catalyst. The Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture was used.     

Deactivation patterns of Mo/Al2O3, Ni–Mo/Al2O3 and Ni–MoP/Al2O3 catalysts in atmospheric residue hydrodesulphurization

In the present work, a comparative study on the deactivation behavior of three types of industrial hydrotreating catalysts, namely, Mo/Al₂O₃, Ni–Mo/Al₂O₃ and Ni–MoP/Al₂O₃, that are used to promote primarily hydrodemetallization (HDM), hydrodesulphurization (HDS) and hydrodesulphurization + hydrodenitrogenation (HDS/HDN) reactions, respectively, in the first, second and third reactor of commercial atmospheric residue desulfurization (ARDS) units was carried out. The main objective of the study was to contribute to a better understanding of the relationship between catalyst type and catalyst deactivation patterns. The used catalysts from these experiments were fully characterized to determine the extent and the cause of deactivation. Special emphasis was paid to understanding the nature of the coke and metal deposition on the used catalysts by applying chemical analysis and various advanced analytical techniques, such as solid-state carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR), temperature-programmed oxidation (TPO), electron probe micro-analysis (EPMA), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The results are discussed scientifically based on the physico–chemical properties of the three catalysts.     

Catalytic activities of Co(Ni)Mo/TiO2–Al2O3 catalysts in gasoil and thiophene HDS and pyridine HDN: effect of the TiO2–Al2O3 composition

The effect of the TiO₂–Al₂O₃ mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO₂ into the support, and particularly over rich- and pure-TiO₂-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO₂. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO₂ content and large differences are observed between the catalysts supported on pure Al₂O₃ and pure TiO₂. In contrast, in the case of the thiophene test, the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al₂O₃- and pure TiO₂-based catalysts is relatively small and dependent on the H₂ pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H₂ partial pressure on the thiophene HDS, and on the effect of H₂S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking.     

Selective catalytic reduction of NO by hydrocarbons on Ga2O3/Al2O3 catalysts

Catalytic properties of supported gallium oxides have been examined for the selective reduction of NO by CH₄ in excess oxygen. The activity was greatly affected by the support; Ga₂O₃/Al₂O₃ (Al₂O₃ supported Ga₂O₃) and Ga₂O₃–Al₂O₃ mixed oxide exhibited high activity and selectivity as comparable to Ga-ZSM-5, while unsupported Ga₂O₃ and the other supported Ga₂O₃ were ineffective. For Ga₂O₃/Al₂O₃, the activity changed with Ga₂O₃ content, and was highest at about 30 wt% Ga₂O₃, which corresponds to a theoretical monolayer coverage. Gallium oxide highly dispersed on Al₂O₃ is considered to be responsible for the high activity and selectivity. The reaction characteristics of Ga₂O₃/Al₂O₃ were studied and compared with Ga-ZSM-5 and Co-ZSM-5. Ga₂O₃/Al₂O₃ exhibited the highest activity and selectivity at high temperature. In addition, Ga₂O₃/Al₂O₃ showed higher tolerance against water than Ga-ZSM-5. C₃H₈ and C₃H₆ were also evaluated as reducing agents, and Ga₂O₃/Al₂O₃ showed higher activity than Ga-ZSM-5 above 723 K achieving almost complete reduction of NO to N₂.     

Preparation of Co–Mo/B2O3/Al2O3 catalysts for hydrodesulfurization: Effect of citric acid addition

The effect of citric acid (CA) addition was studied on the HDS of thiophene over Co–Mo/(B)/Al₂O₃ catalysts. The catalysts were characterized by means of LRS, Mo K-edge EXAFS, NO adsorption capacity measurements, and UV–vis spectra. The catalysts were subjected to a chemical vapor deposition (CVD) technique using Co(CO)₃NO as a precursor of Co in order to get deeper insights into the effect of citric acid addition. It was shown that the HDS activity was enhanced by the citric acid addition up to the CA/Mo mole ratio of around 1 and leveled off with further addition. The amount of Co anchored by the CVD was increased by the addition of citric acid, suggesting an increase in the dispersion of MoS₂ particles on the catalyst by the simultaneous presence of Co, Mo and citric acid, in conformity with the increase in the NO adsorption capacity. In contrast to Co–Mo catalysts, the edge dispersion of MoS₂ particles in Mo/B/Al₂O₃ was not affected by the addition of citric acid. The LRS, UV–vis spectra and Mo K-edge EXAFS showed that Co–CA and Mo–CA surface complexes are formed by the addition of citric acid. The Co–CA surface complex is more preferentially formed on CoMo/Al than on CoMo/B/Al, in agreement with a greater promoting effect of citric acid at a lower CA/Mo mole ratio for CoMo/Al than for CoMo/B/Al.     

Low-temperature 1,3-butadiene hydrogenation over supported Pt/3d/γ-Al2O3 bimetallic catalysts

Low-temperature 1,3-butadiene hydrogenation is used as a probe reaction to investigate the hydrogenation activity over several γ-Al₂O₃ supported Pt/3d (3d = Co, Ni, Cu) bimetallic catalysts. Batch and flow reactor studies are employed to quantify the kinetic activity and steady-state conversion, respectively, of each catalyst. Transmission electron microscopy (TEM) is utilized to characterize particle sizes and extended X-ray absorption fine structure (EXAFS) measurements are performed to verify the Pt–3d bimetallic bond formation. Pulse carbon monoxide chemisorption measurements are also performed to characterize the number of active sites. Additionally, density functional theory (DFT) calculations are included to determine the binding energies of 1,3-butadiene and atomic hydrogen on the corresponding model surfaces. The binding energies of the adsorbates are found to correlate with the hydrogenation activity, allowing for use of such correlation to potentially predict hydrogenation catalysts with enhanced activity based on the binding energies of the adsorbates of interest.     

Modeling preferential CO oxidation over promoted Au/Al2O3 catalysts using decision trees and modular neural networks

In this work, the experimental data for CO oxidation over promoted Au/Al₂O₃ catalysts were analyzed using decision trees and modular neural networks. The full dataset was first classified by decision trees to identify and select the conditions for high catalytic activity; then the reduced dataset containing only the promising data were modeled using neural networks, at which the compositional and operating variables were processed in a modular manner to be able to model their effects together but treat them separately. It was found that operating variables were more influential on catalytic activity than catalyst compositional variables. The temperature was found to be the most significant operating variable while Mg and Mn were the best performing promoters. It was also concluded that decision trees and neural networks can complement each other to extract easily comprehensible knowledge, and they can be used for similar catalytic systems for the same purpose.     

Fe2O3/Al2O3 catalysts for the N2O decomposition in the nitric acid industry

Fe₂O₃ catalysts supported on Al₂O₃ were used to remove nitrous oxide from the nitric acid plant simulated process stream (containing O₂, NO and H₂O). Catalysts were prepared by the coprecipitation method and were characterized for their physico-chemical properties by BET, XRD, AFM and TPR analysis. A strong influence of the post-preparation heating conditions on the structural and catalytic properties of the catalysts has been evidenced. Laboratory tests revealed 95% conversion of N₂O at temperature 750 °C and a slight decrease in activity in the presence of H₂O and NO. The catalysts were inert towards decomposition of NO. The pilot-plant reactor and real plant studies (up to 3300 h time-on-stream) confirmed high activity and very good mechanical stability of the catalysts as well as no decomposition of nitric oxide.     

The interaction of cobalt species with alumina on Co/Al2O3 catalysts prepared by atomic layer deposition

Alumina supported cobalt catalysts were prepared by atomic layer deposition (ALD) of cobalt acetylacetonate precursors (Co(acac)₂ and Co(acac)₃). The main modes of interaction between the acetylacetonate precursors and the support were found to be the exchange reaction between the alumina OH-groups and the acac-ligands of the precursor and dissociative adsorption on coordinatively unsaturated Al³⁺ sites. The amount of precursor that could adsorb on the support was determined by steric hindrance. Samples were prepared using 1–5 reaction cycles, i.e. subsequent precursor addition (Co(acac)₂) and calcination, resulting in catalysts containing ca. 3–10 wt.% Co. Samples were also prepared where the last calcination step was omitted, i.e. uncalcined catalysts. Calcination at 450 °C decreased the reducibility of the Co(acac)₂/Al₂O₃ catalysts due to formation of a cobalt oxide phase strongly interacting with the support and aluminate type surface species. The reducibility increased with metal loading on both calcined and uncalcined catalysts; however the reducibility of the calcined catalysts remained lower than of the uncalcined ones. The dispersion was found to be lower on the calcined catalysts. The cobalt particle sizes on the calcined samples was ca. 8 nm and on the uncalcined 4–5 nm, for cobalt loadings of ca. 6–10 wt.%. Catalytic activity was tested by gas phase hydrogenation of toluene in temperature programmed mode (30–150 °C).     

Al_2O_3负载钯催化剂的制备及催化Suzuki偶联反应的研究

采用浸渍-还原法制备三氧化二铝负载钯催化剂（Pd/Al2O3）,通过ICP-AES、XRD、XPS等分析手段对催化剂的结构和组成进行了表征。考察了溶剂、溶剂与水的比例、碱的种类、反应温度以及反应时间等反应条件对上述制备的催化剂催化Suzuki偶联反应的影响,筛选出最适宜的反应条件。实验结果表明,在1mmol对溴苯乙酮,1.5mmol苯硼酸,2mmol碳酸钾,乙醇∶水=6∶6,反应温度为60℃,反应时间为60min,催化剂加入量为3.5×10-3mmol钯的反应条件下,Suzuki反应收率可达97%以上。     

The active phase of Au–Pd/Al2O3 for CO oxidation

Au–Pd/Al₂O₃ catalyst was prepared by modified impregnation method. It was found that the catalyst calcined in air at 473 K showed higher CO oxidation activity in comparison with the catalysts treated at other temperature. Nitrogen adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure spectroscopy (XANES) techniques were employed to study the relationship between the surface/bulk structures of these catalysts and their catalytic performance. The results indicated the higher activity was attributed to the smaller pore volume and co-existence of PdO and Au⁰ in their surface. The formation of Au_xPd_y alloy was unfavorable for the catalytic reaction.