SBA-15 mesoporous silica modified with rhodium by MDD method and its catalytic role for N<Subscript>2</Subscript>O decomposition reaction

SBA-15 mesoporous silicas modified with rhodium were studied as catalysts for the N₂O decomposition reaction. Rhodium was deposited on SBA-15 by the Molecular Designed Dispersion (MDD) method using Rh(acac)₃ as a precursor of active phase. The same method was used for the deposition of Cu, Fe, Al and Ti. The SBA-15 support modified with metals were characterized with respect to metal loading (EPMA), structure (XRD), texture (BET), morphology (SEM), Rh dispersion (oxygen chemisorption), surface acidity (pyridine adsorption) and chemical nature of introduced copper and iron species (UV–vis-DRS). The rhodium-containing SBA-15 samples were found to be active catalysts for the N₂O decomposition reaction. Deposition of Al on the Rh-loaded catalyst increased its activity. An opposite effect was observed for the samples modified with Cu and Fe.     

Preparation, characterization, and catalytic properties of the Mo2C/SBA-15 catalysts

A series of Mo₂C/SBA-15 catalysts with different Mo contents were prepared by temperature-programmed carburization (TPC). The materials obtained and their oxide precursors (MoO₃/SBA-15) were characterized by Nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), and Fourier transform-infrared (FT-IR) spectroscopy. The activities of the catalysts for deep hydrodesulfurization (HDS) of thiophene were evaluated. The results of N₂ adsorption-desorption isotherms indicated that the surface area and pore diameter of the oxide precursors increase after carburization. The XRD patterns show that Mo₂C particles are highly dispersed in the SBA-15 ordered mesoporous. The test results show that Mo₂C/SBA-15 catalysts have an excellent performance for the deep HDS under the lower temperature region.     

Characterization and catalytic properties of mesoporous CuO/SBA-16 prepared by different impregnation methods

CuO/SBA-16 catalysts were prepared by two different routes - the conventional impregnation method and the modified impregnation method with pH adjustment. These catalysts were characterized by X-ray diffraction (XRD), atomic absorption spectrometry (AAS), N₂ physisorption and hydrogen temperature programmed reduction (H₂-TPR) measurements which reveal that the cubic cagelike (Im3m) pore structure of the parent SBA-16 molecule sieves was well maintained throughout the synthesis. After introduction of Cu, a different CuO dispersion exists on these catalysts. The CuO/SBA-16 prepared by modified impregnation method has a single highly dispersed CuO which is considered as a highly efficient species for hydroxylation of phenol with H₂O₂. CuO/SBA-16 prepared by the conventional impregnation method shows the presence of bulk CuO species which is undesirable for this reaction.     

Nitrous Oxide Reduction with Ammonia and Methane Over Mesoporous Silica Materials Modified with Transition Metal Oxides

Transition metal oxides (Cu, Cr and Fe) were deposited on various mesoporous silicas (MCM-48, SBA-15, MCF and x-MSU) by an impregnation method. Electron microprobe analysis, BET, UV-VIS-DRS and temperature programmed desorption of NH₃ were used for the characterization of the samples. The modified mesoporous silicas were tested as catalysts of the N₂O decomposition and the N₂O reduction using ammonia and methane. The Cu-containing samples presented the highest catalytic activity in the N₂O decomposition, while the Cr- and Fe-modified materials were more active in the reduction of nitrous oxide with NH₃ and CH₄. The type of the silica support strongly influenced the catalytic performance of the studied materials.     

Synthesis,characterization, and catalytic performance of highly dispersed vanadium grafted SBA-15 catalyst

Vanadium oxide grafted on mesoporous silica SBA-15 has been synthesized using a controlled grafting process. Its structure has been thoroughly investigated using different characterization techniques, including N₂-physisorption, X-ray diffraction, transmission electron microscopy (TEM), Raman spectroscopy, H₂ temperature-programmed reduction, X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS). The spectroscopic results revealed that under dehydrated conditions, the grafted vanadium domains are highly dispersed on the SBA-15 surface, composed predominately of isolated VO₄ units with distorted tetrahedral coordination. The suggested (SiO)₃VO sites on the silica surface include one short bond (～1.54 Å) and three long bonds (1.74 Å). Methanol oxidation was used as a chemical probe reaction to examine the catalytic properties of these catalysts. At low vanadium loading, the vanadium species grafted on the surface show structural properties similar to those of vanadium-incorporated MCM-41 catalyst. However, the present mesoporous V-SBA-15 catalysts in the oxidation of methanol to formaldehyde show remarkable catalytic performance compared with that of VO_x/SBA-15 catalysts synthesized through a conventional wet impregnation method, which has been attributed to the homogeneous dispersion and uniformity of the catalytic vanadium species achieved on the SBA-15 support with large pore diameter and surface area. The acidic properties of V-SBA-15 was investigated by pyridine temperature-programmed desorption, which indicated the existence of both Lewis and Brönsted acid sites of the surface.     

Methanol synthesis pathway over Cu/ZrO2 catalysts: a time‐resolved DRIFT 13C‐labelling experiment

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to characterize a series of Cu/Ce/Al₂O₃ catalysts. Catalysts were prepared by incipient wetness impregnation using metal nitrate and alkoxide precursors. Catalyst loadings were held constant at 12 wt% CuO and 5.1 wt% CeO₂. Mixed oxide catalysts were prepared by impregnation of cerium first, followed by copper. The information obtained from surface and bulk characterization has been correlated with CO and CH₄ oxidation activity of the catalysts. Cu/Al₂O₃ catalysts prepared using Cu(II) nitrate (CuN) and Cu(II) ethoxide (CuA) precursors consist of a mixture of copper surface phase and crystalline CuO. The CuA catalyst shows higher dispersion, less crystalline CuO phase, and lower oxidation activity for CO and CH₄ than the CuN catalyst. For Cu/Ce/Al₂O₃ catalysts, Ce has little effect on the dispersion and crystallinity of the copper species. However, Cu impregnation decreases the Ce dispersion and increases the amount of crystalline CeO₂ present in the catalysts, particularly in Ce modified alumina prepared using cerium alkoxide precursor (CeA). Cerium addition dramatically increases the CO oxidation activity, however, it has little effect on CH₄ oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic decomposition of N2O over supported rhodium catalysts: high activities of Rh/USY and Rh/Al2O3 and the effect of Rh precursors

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over Al₂O₃-supported and zeolite-supported Rh catalysts. The activities of Rh/Al₂O₃ and Rh/USY (ultrastable Y zeolite) catalysts prepared from Rh(NO₃)₃ were higher than those of Rh/ZSM-5 and Rh/ZnO reported in the literature, while the activity of a Rh/Al₂O₃ catalyst prepared from RhCl₃ was suppressed severely in spite of the high H/Rh and CO/Rh values. The catalytic activity of N₂O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. This revised version was published online in July 2006 with corrections to the Cover Date.     

DRIFTS study of the catalytic N2O reduction by SO2 on FeZSM-5

SO₂ has been recognized as an effective reducing agent for N₂O over iron-containing zeolite catalysts, lowering the operation temperature up to 100 K with respect to the direct N₂O decomposition. This unique behavior contrasts with the common poisoning effect of SO₂ over other active de-N₂O metals (e.g. Co, Cu, Rh, and Ru). The formation of surface sulfates has been generally posed as the main cause for catalyst deactivation by SO₂. Through the use of in situ infrared spectroscopy (DRIFTS), we show that steam-activated FeZSM-5 indeed builds up stable sulfate species during the N₂O + SO₂ reaction. Significant amounts of sulfur were detected in the used catalyst by elemental analysis and X-ray photoelectron spectroscopy. However, the enhanced N₂O conversion is remarkably stable, indicating that the reducing action by SO₂ and the sulfation of the surface are decoupled. The resulting sulfate species are thus spectators in the catalytic process and do not block or alter the structure of the active sites for N₂O reduction and decomposition.     

Preparation of Keggin and Preyssler Heteropolyacid Catalysts on Amine-modified SBA-15 and Their Catalytic Performances in Esterification of n-Butanol with Acetic Acid

The Keggin and Preyssler-structured tungstophosphoric acid catalysts anchored on the surface of modified SBA-15 (KNS and PNS) by grafting amine groups into system, and were characterized by infra-red spectroscopy, X-ray diffraction, N₂-adsorption, Hammett indicator and UV-Vis spectroscopy. Their catalytic behaviors were investigated in the esterification of n-butanol with acetic acid. Characterization results for obtained catalysts verified the ordered hexagonal mesostructure of SBA-15 and preservation of the structures of heteropolyanions on amine-modified SBA-15. KNS and PNS catalysts with the 37 and 25% loadings of Keggin and Preyssler acids exhibited considerable conversions of n-butanol of 61.2 and 63.8% with both 100% selectivity for n-butyl acetate in the esterification reaction, respectively. Especially, tests of six-cycle reaction revealed good reusabilities of KNS and PNS due to their excellent water-resistance properties, and in contrast, the catalysts prepared by direct impregnation lost their high activities immediately at their second cycles. Active sites on the amine-modified SBA-15 retained the Keggin or Preyssler structure after reaction demonstrated by IR analysis. Also, reaction conditions such as the amount of catalyst, reaction time and temperature were explored.     

A study on effect of Rh precursor and La addition on N2O decomposition over Rh catalyst

The decomposition of N₂O in the presence of oxygen was studied on Rh/CeO₂ and Rh/La₂O₃–CeO₂ catalysts prepared by wet impregnation method. The conversion of N₂O decomposition increased as the Rh loading increased, and the Rh-chloride catalyst showed a poor activity than the Rh-nitrate catalyst. XPS and IC/ICP analysis confirmed that the Rh-chloride catalyst's low activity caused since Rh-chloride catalyst had the some RhCl₃ species. N₂O decomposition rate over Rh/La₂O₃–CeO₂ catalysts decreased as the La loading increased due to the SMSI effect between Rh and CeO₂. H₂ TPR confirmed that the activity and reducibility of the catalyst were closely related.     

Nanocrystalline CeO2 in SBA-15: Performance of Pt/CeO2/SBA-15 Catalyst for Water-gas-shift Reaction

CeO₂ particles confined within the pores of an SBA-15 mesoporous silica host were prepared by incipient wetness impregnation (IMP) and deposition precipitation (DP) methods. The materials were characterized by XRD, N₂-adsorption and temperature programmed reduction (TPR) to evaluate the structure, texture, and redox properties. The preparation procedure had significant impact on the assembling mode of CeO₂ inside the SBA-15 mesopores. A high dispersion of CeO₂ particles was achieved via DP, whereas the dispersion of CeO₂ prepared by IMP was found to be inhomogeneous and CeO₂ partially blocked the pores. The CO conversion in the water-gas-shift reaction was enhanced over 1 wt% Pt supported on CeO₂-modified SBA-15 obtained by DP.     

Cu/SBA-15 is an Efficient Solvent-Free and Acid-Free Catalyst for the Rearrangement of Benzaldoxime into Benzamide

Abstract  

Cu/SBA-15 catalysts with various Cu loadings in the range of 5–20 wt% were prepared by an impregnation method and characterized by N₂ adsorption, X-ray diffraction, temperature programmed reduction and X-Ray photoelectron spectroscopic techniques. Cu/SBA-15 catalysts are found to be highly active and selective for the Beckmann rearrangement of benzaldoxime into benzamide under solvent-free and acid-free conditions.     

Characterization and reductive amination of cyclohexanol and cyclohexanone over Cu/ZrO2 catalysts

Reductive amination of cyclohexanol/cyclohexanone was studied over copper catalysts supported on zirconia. The effect of copper loading and dispersion was studied on the activity and selectivity of the reaction. A series of zirconia supported copper catalysts with varying copper loadings (1–15 wt%) were prepared by incipient wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD) and temperature-programmed reduction (TPR). Copper dispersion and metal area were determined by N₂O decomposition by passivation method. X-ray diffraction patterns indicate the presence of crystalline CuO phase from 4.0 wt% Cu on zirconia. TPR patterns reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The acid–base properties of catalysts were investigated by means of a model reaction cyclohexanol dehydrogenation to cyclohexanone and compare with the results of TPD of ammonia, which allows to measure the acid–base properties of the support and to investigate the changes in surface acidity or basicity, resulting from the metal impregnation.     

SBA-15 as Support for MoS2 and Co-MoS2 Catalysts Derived from Thiomolybdate Complexes in the Reaction of HDS of DBT

Molybdenum sulfide and cobalt-molybdenum sulfide catalysts supported on mesoporous SBA-15 were prepared by thermal decomposition of ammonium thiomolybdate (ATM). SBA-15 was synthesized at 353 K and 413 K to obtain pore diameters of about 6 and 9 nm, respectively. The (Co)-MoS₂/SBA-15 catalysts were characterized with X-ray diffraction (XRD), N₂-physisorption and high-resolution transmission electron microscopy (HRTEM). HRTEM images give evidence for the presence of a poorly dispersed MoS₂ phase with long MoS₂ slabs and a pronounced MoS₂ stacking. The catalytic performance in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) was examined at T = 623 K and P = 3.4 MPa. The Co-MoS₂/SBA-15 materials show a relatively high catalytic activity with a strong preference for the direct desulfurization (DDS) pathway. This is an interesting result in view of the significant stacking of MoS₂ particles and the size of the slabs. The generation of the catalytically active CoMoS phase and a large number of coordinately unsaturated sites (CUS) may explain the high performance of Co promoted MoS₂/SBA-15 catalysts in the HDS reaction. A confinement effect of the mesoporous channels of SBA-15 is observed for the unpromoted MoS₂/SBA-15 catalysts. SBA-15 with 9 nm channel diameter with 11 wt.% Mo loading shows a higher selectivity for the hydrogenation pathway than SBA-15 with 6 nm channel and 16 wt.% Mo loading.     

An investigation into the effect of Cs promotion on the catalytic activity of NiO in the direct decomposition of N2O

A series of Cs promoted NiO catalysts have been prepared and tested for direct decomposition of N₂O. These catalysts are characterized by BET surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of N₂O (TPD-N₂O) and X-ray photo electron spectroscopy (XPS). The Cs promoted NiO catalysts exhibit higher activity for the decomposition of N₂O compared to bulk NiO. The catalyst with Cs/Ni ratio of 0.1 showed highest activity. The enhancement in catalytic activity of the Cs promoted catalysts is attributed to the change in the electronic properties of NiO. The characterization techniques suggest weakening of Ni–O bond thereby the desorption of oxygen becomes more facile during the reaction. The Cs promoted NiO catalyst is effective at low reaction temperature and also in the presence of oxygen and steam in the feed stream. IICT Communication No: 070523.     

Hydrogenation of CO<Subscript>2</Subscript> to methanol over Au–CuO/SBA-15 catalysts

A series of Au–CuO/SBA-15 catalysts with 1–3 wt% Au and 30 wt% CuO were successfully prepared for CO₂ hydrogenation to methanol by chemical reduction and the following impregnation. The influence of Au content on the physicochemical properties of Au–CuO/SBA-15 catalysts was investigated in terms of ICP-AES, N₂ physisorption, XRD, TEM, N₂O titration, XPS and H₂–TPR technique. The results showed that the as-prepared Au–CuO/SBA-15 catalysts exhibited higher catalytic activity than CuO/SBA-15 catalyst. 2 % Au–CuO/SBA-15 catalyst showed the best catalytic activity with 13.5 % methanol selectivity and 24.2 % CO₂ conversion for CO₂ hydrogenation to methanol. The addition of Au NPs played an important role in improving the catalytic activity for CO₂ hydrogenation to methanol, which may be attributed to the interaction between Au and CuO.     

Catalytic activity of mesoporous V/SBA-15 in the transesterification and esterification of fatty acids

Mesoporous V/SBA-15 with different weight percentages (1, 2.5 and 5 wt%) of vanadia was prepared via the wet impregnation method. The mesoporous nature of the catalysts were investigated, using the X-ray diffraction analysis, N₂ adsorption–desorption isotherm and scanning electron microscope. All the catalysts showed the highly dispersed vanadia was confirmed by the result of the diffuse reflectance UV vis technique. From the NH₃-temperature programmed desorption, it is observed that, the acidity values of the prepared catalysts are in the range 72–102 µmol/g. 5 % V/SBA-15, possesses Bronsted and Lewis acid sites ensured by pyridine-adsorbed Fourier-transform infrared method. The acidity of the catalyst was experimented in the transesterification of sunflower oil. The reaction conditions were optimized with maximum conversion (100 %) of sunflower oil into biodiesel and the activity of the catalyst was found to be more in 5 wt% V/SBA-15 at 140 °C. Different fatty acids like butyric, valeric, caprylic and oleic acid were also studied under optimized conditions, and the isolated product was confirmed from the H¹ NMR spectroscopy.     

Investigation of chromium oxide clusters grafted on SBA-15 using Cr-polycation sol

A comparative study of chromium oxide clusters grafted on mesoporous silica SBA-15 was carried out using samples synthesized by one-pot, impregnation and Cr-polycation sol grafting methods. The nature of CrO_x species incorporated into SBA-15 by direct hydrothermal one-pot method as well as impregnation of Cr(NO₃)₃·9H₂O and Cr-polycation precursors was characterized by XRD, BET isotherms, UV–Vis DRS, FTIR, TGA, O1s XPS, ²⁹Si-MAS NMR, H₂-TPR, NH₃-TPD, SEM and TEM. Powder XRD did not show the presence of Cr₂O₃ in the calcined samples obtained by one-pot method. It, however, shows the rhombohedral clusters of α-Cr₂O₃ dispersed over SBA-15 for CrO_x/SBA-15 samples prepared by impregnation and polycation sol grafting methods. The absorption band at 296 nm, observed for Cr³⁺ in solution, is absent for the aqueous Cr-polycation sol. There is evidence that the presence of chromium precursor in the reaction medium can influence the morphology of SBA-15 as seen in the SEM micrographs. Charge transfer transitions demonstrate the insertion of CrO_x species on SBA-15 matrix synthesized by one-pot method. Cr-polycation grafted SBA-15 sample shows unique vibrational features at 573 and 624 cm^?1 attributed to extra-framework CrO_x species. The ratio of Cr⁶⁺/Cr³⁺ species present in CrO_x/SBA-15 samples depends on the Cr-precursor employed for grafting on SBA-15. One-pot synthesized samples predominantly contain coordinated water (δ_H–O–H at 1,635 cm^?1) on SBA-15 while impregnated samples show water molecules associated with CrO_x species (δ_H–O–H at 1,594 cm^?1).     

SBA-15 based catalysts in catalytic N2O decomposition in a model tail-gas from nitric acid plants

Nitrous oxide (N₂O) is a greenhouse gas and damages the ozone layer. Nitrous oxide from nitric acid plants is currently the major industrial N₂O source. Many catalysts are active for pure N₂O decomposition, but few are effective under realistic conditions, due to the relatively low N₂O concentration compared to those of inhibitors present in the exhaust gases, i.e. H₂O, O₂ and NO_x. In the present work, Si-SBA-15 and Al-SBA-15 were used to prepare Fe, Ru or Rh catalysts by ion-exchange, impregnation or precipitation method. The effect of steam treatment was also studied. Their activities were evaluated in an automated six-flow reactor system using a model tail-gas under conditions representative for nitric acid plants.

The performance depends on the metal species and preparation method. When the carrier, preparation method and metal loading are the same, the activity decreases as follows: Rh > Ru > Fe. Steam-treatment has little influence on catalytic activity unlike for FeZSM-5 catalysts. Impregnated Rh on Al-grafted SBA-15 catalyst shows the best performance per weight of catalyst. However, per mol of active metal (Rh, Ru and Fe) species, catalysts by ion exchange are better than those by impregnation. It is concluded that the improved performance of Rh on Al-grafted SBA-15 is caused by a better dispersion and an enhanced stability due to Al incorporation, but not due to an enhanced acidity thereof.     

Hydrotreatment of heavy oil from a direct coal liquefaction process on sulfided Ni-W/SBA-15 catalysts

A series of Ni-W catalysts supported on SBA-15 with different pore sizes were prepared by incipient wetness impregnation method and characterized by N₂ adsorption-desorption and X-ray diffraction. The hydrogenation of heavy oil (distillation temperature: 320-340 °C) derived from the direct coal liquefaction process using Shengli coal in the presence of sulfided Ni-W/SBA-15 catalysts with different pore sizes were evaluated at 400 °C and initial H₂ pressure of 5.0 MPa. The results showed that the catalyst preparation method and the pore size of the support had a significant influence on the Ni/W crystallite size, hydrodenitrogenation (HDN) and hydrodearomatization (HDA) activities of coal-derived heavy oil. The larger pore could cause the Ni-W/SBA-15 to form larger Ni-W crystallite. The catalysts with largest pore in the range studied displayed highest HDN and HDA activities for upgrading of the coal-derived heavy oil.