Application of Cs salt of 12-tungstophosphoric acid supported on SBA-15 mesoporous silica in NO x storage

Cs salt of 12-tungstophosphoric acid (HPW) was deposited simultaneously at the external surface of the SBA-15 silica microcrystals and inside its mesoporous channels at loading of 60 wt% and Cs/W ratio in the range between 0.9 and 2, followed by impregnation of 1 wt% Pt. The performance of the Pt/CsHPW/SBA-15 composite materials was tested in the NO _x storage. The optimal NO _x storage capacity and efficiency were achieved at Cs/W of 1.5. The dispersion of CsHPW on SBA-15 led to a significant decrease of its crystal size (5–13 nm) compared with bulk HPW and HPW supported on titania (28–29 nm). Pt/CsHPW/SBA-15 displayed lower NO _x absorption capacity but much higher absorption and desorption efficiency than the reference Pt/HPW and Pt/HPW/TiO₂ materials. Consequently, Pt/CsHPW/SBA-15 displayed a better performance in short lean (2 min)—rich (1 min) absorption-desorption cycles. The novel Pt/CsHPW/SBA-15 nanocomposites presents the basis for improved storage material for NO _x removal from lean exhaust gases in highly dynamic aftertreatment technologies.     

Deep HDS over NiMo/Zr-SBA-15 catalysts with varying MoO3 loading

In the present work, with the aim of searching for new, highly effective catalysts for deep HDS, a series of NiMo catalysts with different MoO₃ loadings (6–30 wt.%) was prepared using SBA-15 material covered with ZrO₂-monolayer as a support. Prepared catalysts were characterized by N₂ physisorption, small- and wide-angle XRD, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, SEM-EDX and HRTEM, and their catalytic activity was evaluated in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS). It was observed that ZrO₂ incorporation on the SBA-15 surface improves the dispersion of the Ni-promoted oxidic and sulfided Mo species, which were found to be highly dispersed, up to 18 wt.% of MoO₃ loading. Further increase in metal charge resulted in the formation of MoO₃ crystalline phase and an increase in the stacking degree of the MoS₂ particles. All NiMo catalysts supported on ZrO₂-modified SBA-15 material showed high activity in HDS of 4,6-DMDBT. The best catalyst having 18 wt.% MoO₃ and 4.5 wt.% NiO was almost twice more active than the reference NiMo/γ-Al₂O₃ catalyst. High activity of NiMo/Zr-SBA-15 catalysts and its evolution with metal loading was related to the morphological characteristics of the MoS₂ active phase determined by HRTEM.     

Use of mesoporous SBA-15 for nanostructuring titania for photocatalytic applications

SBA15–TiO₂ samples prepared by introducing titanium with a grafting method and having TiO₂ loadings below 15 wt.% have been characterized by XRF, XRD, IR, porosimetry, SEM, HRTEM, and UV–Visible diffuse reflectance. Differently from the samples reported in the literature characterized by a high TiO₂ loading, no evidences have been found for the presence of titania particles inside or outside the mesopores of SBA-15. Three different titanium species were instead evidenced to be present. The first two derive from the reaction of titanium with silanol groups in the corona area of inner SBA-15 walls leading to the formation of either TiO₄ tetrahedral sites (by reaction by hydroxyl nests of surface defect sites) and/or pseudo-octahedral surface sites anchored by two (or more) Si or Ti ions through bridging oxygens. The third species derives from the reaction of titanium in the regions with high sylanol density, e.g. in the micropores located in the corona of SBA-15 channels, leading to the formation of TiO₂-like nanoareas (probably Si-doped) with dimensions of around 1–2 nm maximum. The potential interest of these materials as photocatalysts, for the presence of a TiO₂-like nanoareas highly accessible by reactants, is discussed.     

A comparative investigation on the properties of Cr-SBA-15 and CrOx/SBA-15

High-surface area and well-ordered mesoporous Cr-incorporated SBA-15 (Cr-SBA-15) and SBA-15-supported chromia (CrO_x/SBA-15) with Cr surface density = 0.05–1.11 Cr-atom/nm² have been prepared, respectively, using the one-step synthesis and incipient wetness impregnation method, and characterized by AAS, XRD, BET, ESEM, TEM, XPS, laser Raman, UV-Vis, FT-IR, and H₂-TPR. It is observed that the Cr-SBA-15 and CrO_x/SBA-15 samples showed an evolution of surface morphology from long chain-shaped to short rod-like and further to an irregularly spherical architecture at elevated Cr content, which might arise from the interaction of Cr ions or CrO_x domains with SBA-15. There were co-presence of tetrahedrally coordinated mono- and poly-chromate (Cr⁶⁺) as well as octahedrally coordinated Cr³⁺ species in Cr-SBA-15 and CrO_x/SBA-15, with the Cr⁶⁺ species being dominant at Cr surface density ≤0.22 Cr-atom/nm² in Cr-SBA-15 and Cr ≤0.54 Cr-atom/nm² in CrO_x/SBA-15, whereas the amount of the Cr³⁺ species increased markedly at Cr surface density ≥0.53 Cr-atom/nm² due to the formation of crystal Cr₂O₃ phase. Maximal Cr incorporation into Cr-SBA-15 and one monolayer surface CrO_x coverage on CrO_x/SBA-15 occurred at Cr surface density ≤0.53 Cr-atom/nm² and <1.11 Cr-atom/nm², respectively. The CrO_x/SBA-15 samples exhibited better reducibility than the Cr-SBA-15 samples, with the best reducibility exhibited at Cr surface densities of 0.54 and 0.12 Cr-atom/nm², respectively.     

Synthesis of Ti-containing SBA-15 materials and studies on their photocatalytic decomposition of orange II

Titanium substituted SBA-15 mesoporous materials have been successfully prepared by conventional hydrothermal method and they were also used as support on TiO₂ loaded SBA-15 photocatalysts. The synthesized materials were characterized by XRD, UV–vis DRS, FT-IR, BET and TEM. We also examined the activity of these materials as photocatalysts for the decomposition of orange II. The incorporation of titanium into framework of SBA-15 makes the pore diameter and pore volume to decrease and slightly decreases the surface area compared to SBA-15. In addition, the pore size distribution becomes broaden with an increase of titanium amount in the SBA-15 framework. For Ti-SBA-15 and TiO₂ loaded Ti-SBA-15 photocatalysts, the IR absorption at 960 cm⁻¹ commonly accepted the characteristic vibration of Ti–O–Si bond. From the TEM images, the regular silica morphology is maintained in the case of Ti-SBA-15(Si/Ti = 50) but the Ti-SBA-15 sample having Si/Ti ratio = 10 partially destroys the hexagonal highly ordered structure and the mesopore structure is disappeared by the clogging of mesopore channels by the titanium dioxides particles for the 50 wt.% TiO₂/Ti-SBA-15 samples. The photocatalytic activity increases with an increase of Ti content (decrease of Si/Ti ratio) and with an increase of TiO₂ loading content.     

Hydrotreating of gas oil on SBA-15 supported NiMo catalysts

The siliceous and the metal substituted (B or Al)-SBA-15 molecular sieves were used as a support for NiMo hydrotreating catalysts (12 wt.% Mo and 2.4 wt.% Ni). The supports were characterized by X-ray diffraction (XRD), scanning electron microscopy and N₂ adsorption–desorption isotherms. The SBA-15 supported NiMo catalysts in oxide state were characterized by BET surface area analysis and XRD. The sulfided NiMo/SBA-15 catalysts were examined by DRIFT of CO adsorption and TPD of NH₃. The HDN and HDS activities with bitumen derived light gas oil at industrial conditions showed that Al substituted SBA-15 (Al-SBA-15) is the best among the supports studied for NiMo catalyst. A series of NiMo catalysts containing 7–22 wt.% Mo with Ni/Mo weight ratio of 0.2 was prepared using Al-SBA-15 support and characterized by BET surface area analysis, XRD and temperature programmed reduction and DRIFT spectroscopy of adsorbed CO. The DRIFT spectra of adsorbed CO showed the presence of both unpromoted and Ni promoted MoS₂ sites in all the catalysts, and maximum “NiMoS” sites concentration with 17 wt.% of Mo loading. The HDN and HDS activities of NiMo/Al-SBA-15 catalysts were studied using light gas oil at temperature, pressure and WHSV of 370 °C, 1300 psig and 4.5 h⁻¹, respectively. The NiMo/Al-SBA-15 catalyst with 17 wt.% Mo and 3.4 wt.% of Ni is found to be the best catalyst. The HDN and HDS activities of this catalyst are comparable with the conventional Al₂O₃ supported NiMo catalyst in real feed at industrial conditions.     

Isomerization of n-hexane over mono- and bimetallic Pd–Pt catalysts supported on ZrO2–Al2O3–WOx prepared by sol–gel

The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO₂ (70, 85 wt.%)–Al₂O₃ (15, 0 wt.%)–WO_x (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N₂ physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WO_x and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO₃ bulk phase. The catalysts increased their S_BET for about 15% promoted by Al₂O₃ addition. Various oxidation states of WO_x species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WO_x species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W⁶⁺ and reduced-state WO_x species (either W⁴⁺ or W⁰). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers.     

Surface properties and reactivity of Cu/γ-Al2O3 catalysts for NO reduction by C3H6: Influences of calcination temperatures and additives

The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al₂O₃ catalysts on the surface properties and reactivity for NO reduction by C₃H₆ in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al₂O₃ catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al₂O₃ and 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalysts calcined at 1073 K possess a CuAl₂O₄ phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C₃H₆ shows that the CuAl₂O₄ is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K, although these catalysts possess the same CuAl₂O₄ phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K is attributed to the formation of less active CuAl₂O₄ phase with high aggregation and preferential promotion of C₃H₆ combustion to CO_x by MnO₂. The engine dynamometer test for NO reduction shows that the C₃H₆ is a more effective reducing agent for NO reduction than the C₂H₅OH. The maximum reactivity for NO reduction by C₃H₆ is reached when the NO/C₃H₆ ratio is one.     

Effect of Zr-SBA-15 support on catalytic functionalities of Mo, CoMo, NiMo hydrotreating catalysts

SBA-15 and ZrO₂ (10–50 wt.%) containing SBA-15 mesoporous materials were prepared by direct and post-synthesis methods. Characterization using low angle XRD, pore size distribution, CO₂ chemisorption indicate that hexagonal mesoporous structure is retained even after ZrO₂ addition (25 wt.%). Mo, CoMo and NiMo catalysts prepared using these supports were examined by XRD, oxygen chemisorption, temperature programmed reduction (TPR). The catalysts were tested for hydrodesulfurization (HDS) of thiophene and hydrogenation (HYD) of cyclohexene. HDS of thiophene for 8%Mo, 3%Co8%Mo, and 3%Ni8%Mo increases with increasing ZrO₂ loading in SBA-15 up to 25 wt.%. Oxygen chemisorption and TPR hydrogen consumption indicated that the molybdenum dispersion and anion vacancies, and catalytic activities are significantly influenced by ZrO₂ content in Zr-SBA-15. A comparison indicated that TiO₂-SBA-15, ZrO₂-SBA-15 supported CoMo catalysts show higher activities for hydrodesulfurization.     

SBA-15 supports modified by Ti and Zr grafting for NiMo hydrodesulfurization catalysts

A series of Ti- and Zr-containing mesoporous SBA-15 supports and their respective NiMo catalysts were prepared to study the effect of the Ti and Zr loading into the support on the characteristics of Ni and Mo surface species and their catalytic activity in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS). Ti and Zr-containing SBA-15 solids with different metal loading (up to 19 wt.% of TiO₂ or 22 wt.% of ZrO₂) were prepared by chemical grafting. The solids prepared were characterized by N₂ physisorption, X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR), chemical analysis and HRTEM. The results show that Ti- and Zr-SBA-15 supports with highly dispersed Ti and Zr species can be obtained without substantial loss of SBA-15 characteristics. Zr grafted species showed somewhat better dispersion on the SBA-15 surface than the corresponding Ti counterparts. It was found that TiO₂ and, especially, ZrO₂ incorporation in the SBA-15 support leads to stronger interaction of Mo and Ni species with the support providing better dispersion to the oxidic and sulfided metal species (XRD, TPR, HRTEM). NiMo catalysts supported on Ti- and Zr-containing SBA-15 showed high activity in 4,6-dimethyldibenzothiophene HDS. It can be concluded therefore that SBA-15 materials grafted with Ti or Zr species show promising features as supports for Mo-based hydrotreating catalysts.     

Oxidative gas phase carbonylation of methanol to dimethyl carbonate over chloride-free Cu-impregnated zeolite Y catalysts at elevated pressure

Incipient wetness impregnation of zeolite Y with copper(II) nitrate solution and inert activation at 650 °C led to active catalysts for the oxidative carbonylation of methanol to dimethyl carbonate in the gas phase. Activities were measured under elevated pressure (0.4–1.6 MPa) with feed compositions of CO/MeOH/O₂ = 40/20/6–1.5 vol.% (balanced by N₂) over zeolite Y loaded with 10–17 wt.% copper. It could be shown that inert activation at 650 °C enhanced the activity, and that Cu loading of 14–17 wt.% gave the best performance. By combined XRD, TEM, TPR and DRIFT characterization it was found that the inert activation initiated dispersion of crystalline CuO, auto-reduction of Cu²⁺ to Cu⁺ and redistribution of copper ions with enrichment inside the supercages of the zeolite. The O₂ content of the feed was found to control the selectivity to dimethyl carbonate. Dimethyl carbonate selectivities of 70–75% were achieved within the temperature range of 140–170 °C at an O₂ content of 1.5 vol.%. This allowed space-time yields of dimethyl carbonate up to 632 g l_cat⁻¹ h⁻¹ at methanol conversions of 5–12%. Formation of the main side product, dimethoxymethane, was surprisingly affected by CO, which is not in line with suggested reaction pathways. A mechanism is proposed including formation of surface carbonate structures as common intermediate.     

High loading of short WS2 slabs inside SBA-15: promotion with nickel and performance in hydrodesulfurization and hydrogenation

Layered nanoslabs of a WS₂ phase with a well-defined hexagonal crystalline structure, average slab length of 3.6 nm, and stacking number of 3.2 were inserted into the nanotubular channels of SBA-15, an ordered pure silica material (surface area of 800 m²/g, uniform mesopore diameter of 6.5 nm) at loadings up to 60 wt.%. Sonication of a slurry containing SBA-15 in a W(CO)₆–sulfur–diphenylmethane solution yielded an amorphous WS₂ phase inside the mesopores. By sulfidation with 1.5% dimethyldisulfide in toluene under a hydrogen flow at 593 K and 5.4 MPa, the amorphous phase was transformed into hexagonal crystalline WS₂ nanoslabs (as shown by XRD, HRTEM, and selected area electron diffraction (SAED)). The WS₂ nanoslabs were distributed exclusively inside the mesopores in a uniform manner (HRTEM, quantitative microanalysis), without blocking the pores (N₂-sorption), and were oriented with their edge planes toward the support surface. This study constitutes the first report of such a combination of high loading of a well-defined crystalline catalytic phase into the nanotubular channels of mesoporous silica without blocking them. The first well-resolved HRTEM images of the well-defined crystalline catalytic phase (WS₂) inside the SBA-15 nanotubes are presented. A Ni component was introduced into the WS₂/SBA-15 composite by impregnation from an aqueous solution of nickel acetate. It increased the catalytic activity up to a Ni/W ratio of 0.4. In the hydrodesulfurization (HDS) of dibenzothiophene and the hydrogenation (HYD) of toluene, the activity of the optimized NiWS/SBA-15 catalyst was 1.4 and 7.3 times higher, respectively, than that of a sulfided commercial CoMo/Al₂O₃. This finding illustrates the excellent potential of high loading NiWS/SBA-15 catalysts for deep hydrotreatment of petroleum feedstocks.     

Sites for CO2 activation over amine-functionalized mesoporous Ti(Al)-SBA-15 catalysts

Activation of CO₂ and its utilization in the synthesis of chloropropene and styrene carbonates over functionalized, mesoporous SBA-15 solids, have been investigated. The surface basicity of SBA-15 was modified with nitrogen-based organic molecules of varying basicity viz., alkyl amines (–NH₂), adenine (Ade), imidazole (Im) and guanine (Gua). The surface of SBA-15 was also functionalized with Ti⁴⁺ and Al³⁺ species. The acid–base properties of these modified SBA-15 materials were investigated by temperature-programmed desorption (TPD) and diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy. NH₃ and pyridine were used as probe molecules for acid sites, while CO₂ was used to characterize the basic sites. CO₂ was activated at the basic amine sites forming surface carbamate species (IR peaks: 1609 and 1446 cm⁻¹). The latter reacted further with epoxides adsorbed on the acid sites forming cyclic carbonates. A correlation between the intensity of the IR peak at 1609 cm⁻¹ and cyclic carbonate yield has been observed. The cyclic carbonate yields were higher when both the acid and base functionalities were present on the surface. The Ti- and Al-SBA-15 functionalized with adenine exhibited the highest catalytic activity and selectivity. There is an optimal dependence (“volcanic plot”) of the yield of cyclic carbonates on the desorption temperature, T_max(CO₂) in the TPD experiments. These solid catalysts were structurally stable up to 473 K and could be recycled for repeated use. In addition to density, the strength and type of amine sites play a crucial role on CO₂ activation and utilization.     

Nickel cuprate supported on cordierite as an active catalyst for CO oxidation by O2

The physicochemical, surface and catalytic properties of 10 and 20 wt% CuO, NiO or (CuO–NiO) supported on cordierite (commercial grade) calcined at 350–700 °C were investigated using XRD, EDX, nitrogen adsorption at −196 °C and CO oxidation by O₂ at 220–280 °C. The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg₂Al₄Si₅O₁₈). Loading of 20 wt% CuO or NiO on the cordierite surface followed by calcination at 350 °C led to dissolution of a limited amount of both CuO and NiO in the cordierite lattice. The portions of CuO and NiO dissolved increased upon increasing the calcination temperature. Treating a cordierite sample with 20 wt% (CuO–NiO) followed by heating at 350 °C led to solid–solid interaction between some of the oxides present yielding nickel cuprate. The formation of NiCuO₂ was stimulated by increasing the calcination temperature above 350 °C. However, raising the temperature up to ≥550 °C led to distortion of cuprate phase. The chemical affinity towards the formation of NiCuO₂ acted as a driving force for migration of some of copper and nickel oxides from the bulk of the solid towards their surface by heating at 500–700 °C. The S_BET of cordierite increased several times by treating with small amounts of NiO, CuO or their binary mixtures. The increase was, however, less pronounced upon treating the cordierite support with CuO–NiO. The catalytic activity of the cordierite increased progressively by increasing the amount of oxide(s) added. The mixed oxides system supported on cordierite and calcined at 450–700 °C exhibited the highest catalytic activity due to formation of the nickel cuprate phase. However, the catalytic activity of the mixed oxides system reached a maximum limit upon heating at 500 °C then decreased upon heating at temperature above this limit due to the deformation of the nickel cuprate phase.     

Support effects on structure and activity of molybdenum oxide catalysts for the oxidative dehydrogenation of ethane

The structural and catalytic properties of MoO₃ catalysts supported on ZrO₂, Al₂O₃, TiO₂ and SiO₂ with Mo surface densities, n_s, in the range of 0.5–18.5 Mo/nm² were studied for the oxidative dehydrogenation (ODH) of ethane by in situ Raman spectroscopy and catalytic activity measurements at temperatures of 400–540 °C. The molecular structure of the dispersed surface species evolves from isolated monomolybdates (MoO₄ and MoO₅, depending on the support) at low loadings to associated MoO_x units in polymolybdate chains at high loadings and ultimately to bulk crystalline phases for loadings exceeding the monolayer coverage of the supports used. The nature of the oxide support material and of the Mo–O–support bond has a significant influence on the catalytic behaviour of the molybdena catalysts with monolayer coverage. The dependence of reactivity on the support follows the order ZrO₂ > Al₂O₃ > TiO₂ > SiO₂. The oxygen site involved in the anchoring Mo–O–support is of relevance for the catalytic activity.     

Preparation and characterization of octyl and octadecyl-modified mesoporous SBA-15 silica molecular sieves for adsorption of dimethyl phthalate and diethyl phthalate

Octyl (C₈) or octadecyl (C₁₈)-modified mesoporous SBA-15 silica molecular sieves have been prepared by adding SBA-15 silica molecular sieves to octyltrimethoxysilane or octadecyltrimethoxysilane in toluene at 100 °C, and characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), nitrogen adsorption–desorption measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FTIR spectra shows the presence of methylene (–CH₂–) and methyl (–CH₃) bands on the modified SBA-15. Powder XRD data indicate the structure of modified SBA-15 with octyl or octadecyl groups still remains two-dimensional hexagonal mesostructrure. Brunauer–Emmett–Teller (BET) surface area analysis presents that surface area of octyl- and octadeyl-SBA-15 changed from 647 to 449 and 321 m² g⁻¹, respectively, and SEM images show the decreased size of modified SBA-15 particles. TEM images of modified materials with alkyl groups show the structures remain the same as the parent SBA-15 silica. We also have studied the adsorption capacity of the materials to phthalate esters (dimethyl and diethyl phthalate) by dynamic adsorption experiments on high performance liquid chromatography (HPLC). It is found that the modified materials can increase the adsorption of phthalate esters compared to SBA-15 particles, and the adsorption capacity increased with the increased length of alkyl chain on SBA-15. The maximum dynamic adsorption capacity for diethyl phthalate was 3.9 (C₈-SBA-15) or 4.3 (C₁₈-SBA-15) times higher than that of SBA-15 particles, respectively. The results indicate that alkyl SBA-15 particles could be used for enrichment of phthalate esters in water samples before the further analysis.     

Copper-based efficient catalysts for propylene epoxidation by molecular oxygen

Among a series of SBA-15-supported transition metal oxides with and without modification, the CuO_x/SBA-15 after K⁺ modification exhibited the best catalytic performance for the epoxidation of propylene by molecular oxygen. Potassium was the best modifier among various alkali and alkaline earth metal ions examined, and potassium acetate was a superior precursor of K⁺ for propylene oxide formation. The highest propylene oxide selectivity was obtained over a catalyst with copper content of 1 wt.% and K/Cu molar ratio of 0.7. Kinetic studies reveal that the allylic oxidation mainly proceeds over the CuO_x/SBA-15 providing acrolein as the main partial oxidation product, and the K⁺ modification switches the main reaction route from allylic oxidation to epoxidation. The characterizations suggest that copper species with content of ≤5 wt.% are located in the mesoporous channels of SBA-15 existing mainly as CuO_x clusters and Cu²⁺ ions, and there exists an interaction between K⁺ and the copper species. This interaction is proposed to play pivotal roles in epoxidation of propylene. As compared with other reported Cu-based catalysts for propylene epoxidation, the present catalyst possesses several distinct features.     

A new alumina-supported, not pyrophoric Raney-type Ni-catalyst

Starting with a 50–50 wt.% Al–Ni alloy powder a new process was developed by which an active alumina supported, not pyrophoric Raney-type Ni catalyst is produced. It consists of very finely dispersed nickel of 25–30 wt.% (specific weight of about 1.2). The Ni is not ferromagnetic. The catalyst is applied in all liquid phase hydrogenations where standard Raney-Ni is used, with the same or higher specific activity.

The structure of the catalyst is described using XRD, SAXS, TEM SEM/EDX, and N₂-sorption. The catalytic activity measurements were performed in liquid phase hydrogenations at room temperature and atmospheric pressure.     

CoMo/Ti-SBA-15 catalysts for dibenzothiophene desulfurization

With a view to reducing the sulfur content in diesel fuels, novel desulfurization CoMo catalysts were supported on a Ti-loaded hexagonal mesoporous SBA-15 material. The Ti-SBA-15 substrates were synthesized using triblock copolymers as structure-directing agents. Catalytic activity was assessed in the model reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT), carried out in a batch reactor at T = 623 K and with a total hydrogen pressure of 3.1 MPa. The reaction proceeds via the direct desulfurization route (main route) and the hydrogenation (HYD) pathway. The incorporation of Ti into the SBA-15 afforded catalysts that were more active than the Ti-free counterpart, due to the enhancement of the DDS route in this reaction. This difference was explained in terms of a larger number of coordinately unsaturated sites (CUS) of the metal sulfide on Ti-loaded catalysts. Under steady-state conditions, the CoMoST20 catalyst with a Si/Ti ratio of 20 was the most active among the catalysts studied. Since this catalyst exhibited both Ti⁴⁺ ions incorporated into the SBA-15 framework and separate anatase TiO₂ clusters located on its surface, the activity enhancement on this sample was explained by the larger intrinsic activity of the “Co–Mo–S” phase located on these TiO₂ nanoparticles. The Ti-SBA-15 supports and the CoMo/Ti-SBA-15 catalysts were studied by N₂ adsorption–desorption isotherms, XRD, TEM, FTIR of adsorbed pyridine and NO, UV–vis DRS, TPR, micro-Raman and XPS spectroscopy.     

Novel utilization of mesoporous molecular sieves as supports of cobalt catalysts in Fischer–Tropsch synthesis

Mesoporous molecular sieves (MCM-41 and SBA-15) with different pore diameters have been studied as supports of high loading of Co catalysts, and the performances in FT synthesis have been examined with a fixed bed stainless steel reactor at 2.0 MPa for the purpose of efficient production of C₁₀–C₂₀ fraction as the main component of diesel fuel. The method of exchanging template ions in uncalcined MCM-41 with Co²⁺ ions is effective for holding 10–20% Co within the mesopores while keeping the structure regularity of MCM-41 to some extent, compared with the conventional impregnation method using calcined MCM-41. At 523 K, CO conversion and selectivity to C₁₀–C₂₀ hydrocarbons are both higher at larger loading of 20% Co for the exchanged catalysts with pore diameters of 2.7–2.9 nm. When four kinds of 20% Co/SBA-15 with the diameters of 3.5–13 nm, prepared by the impregnation method using an ethanol solution of Co acetate, are used in FT synthesis at 523 K, the catalyst with the diameter of 8.3 nm shows the largest CO conversion, which is higher than those over MCM-41 supported Co catalysts. At a lower temperature of 503 K, however, the acetate-derived Co is almost inactive. In contrast, the use of Co nitrate alone or an equimolar mixture of the acetate and nitrate as Co precursor drastically enhances the reaction rate and consequently provides high space–time yield (260–270 g C/kg_cat h) of C₁₀–C₂₀ hydrocarbons. The X-ray diffraction and temperature-programmed reduction measurements show that the dependency of the catalytic performance of 20% Co/SBA-15 on its precursor originates probably from the differences in not only the reducibility of the calcined catalyst but also the dispersion of metallic Co. Catalyst characterization after FT synthesis strongly suggests the high stability of the most effective Co/SBA-15 in the dispersion and reducibility of the oxide species and in the mesoporous structure.