Beta Zeolite-Supported Iridium Catalysts by Gas Phase Deposition

In this study, H-beta zeolite-supported iridium catalysts were prepared by atomic layer deposition (ALD) and characterized as such and after different activation treatments. A reference catalyst was prepared by wet impregnation. The samples were tested in decalin ring opening reaction. ALD samples were clearly more active and selective in decalin ring opening compared to impregnated sample. The differences observed in characteristics and activities between ALD samples and impregnated sample are discussed.     

十氢萘选择性加氢开环反应的研究进展

日益严峻的环境问题导致清洁柴油的标准越来越高,而柴油中含量较高的十氢萘等饱和双环化合物的十六烷值低,燃烧性能差,可以对其进行选择性加氢开环反应--即将十氢萘转化为单环烷烃或链烷烃的同时尽量减少反应物分子的碳数损失,以提高油品燃烧性质。首先阐述了十氢萘加氢开环反应机理,并提出B酸位对十氢萘加氢开环反应至关重要,进而介绍了十氢萘开环反应的分子筛载体,并提出Y型分子筛是合适载体,接下来,从金属活性位的角度进行评述,并对比了环烷烃在Pt和Ir两种贵金属上典型的吸附模式,最后,对该领域研究前景进行了展望。     

Synthesis of Ru-modified MCM-41 Mesoporous Material, Y and Beta Zeolite Catalysts for Ring Opening of Decalin

Ru modified MCM-41 mesoporous material, Y and Beta zeolites were synthesized, characterized and investigated in ring opening of decalin. Ru-MCM-41 catalysts were prepared using ion-exchange, impregnation and in situ synthesis methods. Ru-MCM-41, Ru-Y and Ru-Beta zeolite catalysts were characterized using XRD, SEM, EDXA, FTIR, XRF and nitrogen adsorption. Ru modification of MCM-41, Y and Beta zeolites did not influence the parent phase purity of materials. Microporous H-Beta and H-Y catalysts showed larger number of Brønsted acid sites than H-MCM-41 mesoporous material. Method of Ru introduction in MCM-41 was observed to influence conversion of ring opening of decalin and selectivity to ring opening products. Ru-MCM-41-IE catalyst prepared by ion-exchange method exhibited higher conversion of decalin than Ru-MCM-41-IMP and Ru-MCM-41-IS catalysts prepared by impregnation and in situ synthesis methods. Ru-MCM-41-IS catalyst prepared by in situ method showed higher selectivity to ring opening products than Ru-MCM-41-IE and Ru-MCM-41-IMP catalysts.     

Dehydrocyclization of Alkanes Over Zeolite-Supported Metal Catalysts: Monofunctional or Bifunctional Route

The direct catalytic conversion of alkanes into aromatics has found potentially important industrial applications. Initially only alkanes with 6 and more carbon atoms in the chain were concerned. Supported platinum catalysts were found active for the aromatization of alkanes; the drawbacks of these catalysts were their deactivation with time on stream and the existence of simultaneous parallel reactions. Much discussion has been published on the aromatization of C₆₊ alkanes. A bifunctional mechanism which involves both the metal and the acid sites of the support and a monofunctional mechanism involving only the metallic sites operate over, respectively, Pt supported on acidic support and Pt supported on nonacidic support. In the present review the mechanisms proposed for the aromatization of alkanes are described. Over monofunctional Pt catalysts two possible mechanisms prevail: 1,6 ring closure on the Pt surface involving primary and secondary C-H bond rupture, followed by dehydrogenation of the cycloalkanes into aromatics (1,5 ring closure to a lesser extent also contributes to aromatic production); or dehydrogenation of the alkanes into olefins, dienes, and trienes followed by thermal ring closure. Zeolites were found most suitable as support for preparing catalysts more active and more selective in the alkane aromatization. In addition catalysts based on noble metals supported on zeolite appeared more resistant against deactivation by coke. In this review the aromatization of hexane, heptane, and octane over Pt-zeolite catalysts is discussed in detail. Comparisons between different zeolite structures and different dehydrogenation sites are given. In particular a critical analysis of the results and interpretation concerning Pt-KL catalysts strongly suggests that the exceptional high selectivity towards aromatization of n-hexane exhibited by Pt-KL could not be explained by only the nest or constraint effect exerted by the channel dimension and morphology, not by only the terminal cracking properties, not by only the partial electron transfer from the zeolite support to the Pt particles, and not by only the Pt particle size. Zeolite structure also affects the aromatic product distribution, in particular when the alkane contains more than 7 carbon atoms. It is shown how Pt on medium-pore zeolites such as In-ZSM-5, silicalites will favor the aromatization of C₈ alkane isomers into ethylbenzene-styrene with respect to other C₈ aromatics. Aromatization of light alkanes, C₂-C₅, requires the increase of the hydrocarbon chain length up to 6 carbon atoms and higher, followed by cyclization reaction. Recently new processes to convert C₂-C₅ alkanes into aromatics have been disclosed, M2-forming from Mobil, Cyclar from BP-UOP, and Aroforming from IFP-Saluted. In general these processes use bifunctional catalysts possessing a dehydrogenating and an acid function. The catalysts consist of a metal ion or metal oxide supported on a microporous acid solid. In this review we analyze the results concerning mainly platinum supported on pentasil-type zeolite. It is shown that althoug Pt has better dehydrogenating properties as compared with gallium and zinc, the efficiency of catalysts based on Pt-ZSM-5 for light alkane aromatization is less because undersirable reactions such as hydrogenolysis and ethene (olefins) hydrogenation occur on the platinum surface, resulting in the production of unreactive alkanes, CH₂, C₂H₆. These drawbacks could be partially suppressed by alloying Pt and by increasing the reaction temperature.     

Dehydrocyclization of Alkanes Over Zeolite-Supported Metal Catalysts: Monofunctional or Bifunctional Route

The direct catalytic conversion of alkanes into aromatics has found potentially important industrial applications. Initially only alkanes with 6 and more carbon atoms in the chain were concerned. Supported platinum catalysts were found active for the aromatization of alkanes; the drawbacks of these catalysts were their deactivation with time on stream and the existence of simultaneous parallel reactions. Much discussion has been published on the aromatization of C₆₊ alkanes. A bifunctional mechanism which involves both the metal and the acid sites of the support and a monofunctional mechanism involving only the metallic sites operate over, respectively, Pt supported on acidic support and Pt supported on nonacidic support. In the present review the mechanisms proposed for the aromatization of alkanes are described. Over monofunctional Pt catalysts two possible mechanisms prevail: 1,6 ring closure on the Pt surface involving primary and secondary C-H bond rupture, followed by dehydrogenation of the cycloalkanes into aromatics (1,5 ring closure to a lesser extent also contributes to aromatic production); or dehydrogenation of the alkanes into olefins, dienes, and trienes followed by thermal ring closure. Zeolites were found most suitable as support for preparing catalysts more active and more selective in the alkane aromatization. In addition catalysts based on noble metals supported on zeolite appeared more resistant against deactivation by coke. In this review the aromatization of hexane, heptane, and octane over Pt-zeolite catalysts is discussed in detail. Comparisons between different zeolite structures and different dehydrogenation sites are given. In particular a critical analysis of the results and interpretation concerning Pt-KL catalysts strongly suggests that the exceptional high selectivity towards aromatization of n-hexane exhibited by Pt-KL could not be explained by only the nest or constraint effect exerted by the channel dimension and morphology, not by only the terminal cracking properties, not by only the partial electron transfer from the zeolite support to the Pt particles, and not by only the Pt particle size. Zeolite structure also affects the aromatic product distribution, in particular when the alkane contains more than 7 carbon atoms. It is shown how Pt on medium-pore zeolites such as In-ZSM-5, silicalites will favor the aromatization of C₈ alkane isomers into ethylbenzene-styrene with respect to other C₈ aromatics. Aromatization of light alkanes, C₂-C₅, requires the increase of the hydrocarbon chain length up to 6 carbon atoms and higher, followed by cyclization reaction. Recently new processes to convert C₂-C₅ alkanes into aromatics have been disclosed, M2-forming from Mobil, Cyclar from BP-UOP, and Aroforming from IFP-Saluted. In general these processes use bifunctional catalysts possessing a dehydrogenating and an acid function. The catalysts consist of a metal ion or metal oxide supported on a microporous acid solid. In this review we analyze the results concerning mainly platinum supported on pentasil-type zeolite. It is shown that althoug Pt has better dehydrogenating properties as compared with gallium and zinc, the efficiency of catalysts based on Pt-ZSM-5 for light alkane aromatization is less because undersirable reactions such as hydrogenolysis and ethene (olefins) hydrogenation occur on the platinum surface, resulting in the production of unreactive alkanes, CH₂, C₂H₆. These drawbacks could be partially suppressed by alloying Pt and by increasing the reaction temperature.     

Effects of Zeolite Structures, Exchanged Cations, and Bimetallic Formulations on the Selective Hydrogenation of Acetylene Over Zeolite-Supported Catalysts

Supported PdAg bimetallic catalysts were evaluated for the selective hydrogenation of acetylene in the presence of ethylene. The effects of different zeolite structures and cations were investigated using flow reactor studies, with K⁺-β-zeolite supported PdAg showing the lowest activity but highest selectivity comparing to the γ-Al₂O₃ support and other alkaline metal exchanged β-zeolite supports. The K⁺ promoter effect on γ-Al₂O₃ was also tested, which showed that adding K⁺ to γ-Al₂O₃ increased activity and selectivity. Bimetallic catalysts consisting of Pd and a Group IB metal were also compared. It was found that the PdAg bimetallic catalyst had similar activity but better selectivity comparing to PdCu, while the PdAu catalyst showed the highest activity but lowest selectivity.     

SBA-15 Immobilized Ruthenium Carbenes as Catalysts for Ring Closing Metathesis and Ring Opening Metathesis Polymerization

New hybrid catalysts for olefin metathesis were prepared by immobilization of Hoveyda–Grubbs type Ru alkylidenes on a siliceous SBA-15 support via exchange of chloro ligands for substituted carboxylates. Catalysts proved a high activity in ring closing metathesis of 1,7-octadiene and diethyl diallylmalonate, reusability and low Ru leaching. In Ring Opening Metathesis Polymerization of norbornene and cyclooctene, SBA-15 supported catalyst gave higher yields of high-molecular-weight polymers than corresponding catalyst with conventional silica support.     

Reductive Amination of 5-Hydroxymethyl-2-furaldehyde Over Beta Zeolite-Supported Ruthenium Catalyst

Beta-zeolite supported ruthenium catalysts for reductive amination of 5-hydroxymethyl-2-furaldehyde (HMF) with an aqueous solution of ammonia (NH₃ aq.) and molecular hydrogen (H₂) are examined to synthesize the corresponding primary amine of 5-aminomethyl-2-furylmethanol (FAA). Various SiO₂/Al₂O₃ (Si/2Al) ratios of the beta-zeolite support were used to prepare the Ru-based catalysts. It was observed that the Si/2Al ratio was contributed to the catalytic activity, and the Si/2Al?=?150 of beta-zeolite was found to be the most active for Ru catalyzed reductive amination of HMF, affording ca. 70% yield. Characterization techniques were taken to analysis the factors that influence the reactivity of catalysts, and which revealed that not only the ruthenium nanoparticle size but also the ratio of RuO₂ against metallic Ru species were crucial factors for the reactivity of reductive amination of HMF to FAA.

Graphical Abstract

     

In-situ XAFS Analysis of Y Zeolite-Supported Rh Catalysts during High-Pressure Hydrogenation of CO2

In-situ XAFS (X-ray absorption fine structure) analysis under high-pressure, high-temperature reaction conditions was done to clarify the effect of Li doping on the structures of Rh species in Rh ion-exchanged NaY zeolite catalysts (RhY). The analysis showed that Rh species in RhY were reduced at a lower temperature than those in Li-doped RhY (Li/RhY). The reduction of Rh in RhY at a lower temperature was related to the formation of amorphous Rh oxide species during the initial stage of reduction, which was not observed in Li/RhY catalysts. The average particle size of metallic Rh species formed under the reaction conditions was 1.3 nm for RhY catalysts and 0.8 nm for Li/RhY catalysts. During exposure to either CO or air, the metallic Rh species in RhY were more easily subject to structural changes than the metallic Rh species in Li/RhY. These differences in the properties of Rh species between the RhY and Li/RhY catalysts resulted from the replacement of hydroxyl groups on the zeolite surface by O–Li compounds, and caused different catalytic activities during CO₂ hydrogenation.     

Hydrogenolysis of Hydroxymatairesinol Over Carbon-Supported Palladium Catalysts

The natural lignan hydroxymatairesinol was hydrogenolysed to a potential anticarcinogenic substance matairesinol over different carbon-supported palladium catalysts. The reaction was conducted in 2-propanol at 70 °C under hydrogen flow in a stirred glass reactor. The catalysts were characterised by N₂-physisorption, CO pulse chemisorption and pH measurement of aqueous catalyst slurries. The most active catalyst (Degussa-Hüls) gave yields of matairesinol over 90% in 4 h. It was concluded that the acidity of the catalyst had a profound influence on the reaction rate.     

Selective Oligomerization of Glycerol Over Mesoporous Catalysts

In the general context of the development of the use of agricultural products for nonfood applications, particularly in the field of glycerol valorization (coproduct of triglyceride hydrolysis and methanolysis processes), the selective etherification of glycerol to di- and triglycerol was studied. Part of this study consisted in the synthesis and the modification, by different techniques, of cesium containing mesoporous solids of the MCM-41 type in order to make them active, selective and stable catalysts for the target reaction. The catalytic results obtained show that the impregnation method gives the highest activity. Concerning the selectivity of the modified mesoporous catalysts, the best values to (di- + tri-) glycerol (>90%) are obtained over solids prepared by the impregnating or the grafting methods. The cesium-impregnated catalysts can be reused without loss of selectivity. In the presence of lanthanum- or magnesium-containing catalysts, the glycerol dehydration to acrolein is important, whereas this unwanted product is not formed when cesium is used as promoter. Moreover, when compared to homogeneous catalysts, the mesoporous solids induce a different regioselectivity. Finally, as far as the catalyst leaching and stability is concerned, the best results are obtained with the grafted solids, which retain their structure and their specific area after the promoter addition or incorporation. Such property is not observed over impregnated catalysts.     

Methanol Decomposition and Synthesis Over Palladium Catalysts

Palladium is generally active in the catalytic decomposition and synthesis of methanol. The activity of palladium is largely affected by its support. Cerium oxide is an effective support especially when the catalyst is prepared by the coprecipitation or depositionprecipitation method which leads to a strong interaction between palladium and the support. Cationic palladium species formed in the catalyst are probably active species for both decomposition and synthesis while formation of Pd-O-Ce bonding is rather important in the synthesis reaction.     

Complete Oxidation of Benzene Over Perovskite-Type Oxide Catalysts

Catalytic oxidation of benzene was carried out over perovskite-type oxides prepared by evaporation-to-dryness techniques. LaMnO₃ showed higher activity than LaCoO₃ and LaFeO₃ due to higher surface area and higher oxidizing ability for benzene. Effect of Sr substitution for La on the activity of LaMnO₃ depended on the calcination conditions.     

Aminolysis of Styrene Oxide Over Heterogeneous Acidic Catalysts

Silica alumina and silica zirconia mixed oxides are shown to be effective and regioselective catalysts for the aminolysis of styrene oxide under very mild experimental conditions, giving the corresponding primary ??-amino-alcohol in good to excellent yield.     

Alkylation of Naphthalene Over Mesoporous Ga-SBA-1 Catalysts

Alkylation of naphthalene with propylene to diisopropylnaphthalenes (DIPN) for the use as a high-quality solvent was carried out over Ga-SBA-1 mesoporous catalysts. The Ga-SBA-1 catalysts were very active in the alkylation even at 120 °C and the activity increased with amount of Ga incorporated into the framework (n _Si/n _Ga ratio in the range of 17–140). Ga-SBA-1 catalysts showed a rather low isomerization activity and as a result low 2,6-DIPN selectivity. These two peculiarities of Ga-SBA-1 catalysts cause they are promising catalysts for DIPN solvent synthesis.     

Total Oxidation of Dichloromethane Over Metal Oxide Catalysts

Three different transition metals (V, Mn and Cu) supported on TiO₂, MgO and CeO₂, were investigated for their performances in dichloromethane oxidation (500 ppm, 704,867 h^?1) in moist conditions as a model reaction for the destruction of chlorinated volatile organic compounds. The catalysts were prepared by sol–gel method followed by wet impregnation of V, Mn or Cu precursors. The activities were evaluated in the temperature range from 100 to 500 °C with 5 °C min^?1 temperature rise. The orders of activity and selectivity to HCl of the catalysts is CuTi > VMg > CuCe > CuMg. A correlation between acidic properties of support and performances was observed as the activity of copper catalysts followed the acidity order of supports.     

Reaction Routes in Selective Ring Opening of Naphthenes

Hydrogenation and ring-opening of low-quality feedstocks rich in aromatic compounds is a very attractive process for the production of clean diesel fuels. The present work explores the detailed reaction paths of decalin (model compound for dinaphthenes) transformation over a bi-functional solid catalyst. The key steps and reaction intermediates in selective ring-opening have been identified and quantified.