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The distribution of Al atoms in ZSM-5 has been recognized as an important factor in catalytic activity. Here, ZSM-5 zeolites were synthesized from synthetic gels containing various alcohols, including straight- and branched-chains alcohols. The effect of the alcohols in the synthetic gel on the Al distribution in the MFI framework was investigated based on 27 Al MAS NMR, Co(II) ion UV−vis DRS, and constraint index value. Thus synthesized ZSM-5 zeolites were applied to catalysts for the cracking of n -hexane and the methanol-to-olefins (MTO) reactions in order to investigate the impact of the Al distribution on the catalytic properties. A unique Al distribution in the MFI framework was achieved by the use of trimethylolethane (TME) in combination with Na cations, and thus-prepared ZSM-5 catalyst showed a long catalytic life for both the cracking of n -hexane and the MTO reaction.

Titanosilicate molecular sieve (TS-1) is an important commercial catalyst for green production of oxyfunctionalized chemicals such as alcohols, ketones, epoxides, and oximes. Active TS-1 can normally be achieved in the synthetic media strictly free of alkali metal cations (e.g., Na + and K + ). This condition severely raises the purity demands of starting reagents, which greatly increases the production cost. Herein, we developed a method to achieve highly active titanosilicates in the presence of high-concentration alkali metal cations using anionic polymer-based quasi-neutral media. This synthetic route could effectively inhibit the adverse influence of alkali metal cations on the incorporation of active titanium(IV) sites into the framework of titanosilicate, directly affording the maximal framework titanium content (2.0 wt.%) with almost 100% yield. This development shows a great commercial potential and opens the possibility of preparing silica-based molecular sieves/zeolites in non-fluoride neutral media.

The catalytic cracking of n -hexane to selectively produce propylene on the MCM-22 catalysts dealuminated by nitric acid treatment was carried out as a model reaction of naphtha cracking. The nitric acid treatment of MCM-22 precursors under severe conditions followed by calcination at 823 K has been proven to be an effective dealumination method for MCM-22 zeolite. At a high n -hexane conversion of 90%, the dealuminated MCM-22 (D-MCM-22) catalyst with Si/Al = 34 showed a higher propylene selectivity (41 C-%) than H-ZSM-5 and H-Beta catalysts with similar acid amounts. Moreover, D-MCM-22 showed a stability comparable to H-ZSM-5 and much higher than H-Beta catalyst. This would be due to the selective removal of acid sites within supercages, suppressing coke formation and the resultant deactivation.

Selective oxidation of alcohols to aldehydes/ketones with O2 over a series of supported gold catalysts was studied. The catalytic performance depends strongly on the support. It is also strongly influenced by the preparation method and the pH value and stirring rate during the co-precipitation process as a result of their effect on the structure of the support and the particle size and electronic state of gold. The Au/CuO co-precipitated at pH 10 and stirring rate 100 rpm showed high activity, selectivity, and stability. The reaction might occur via oxidative dehydroxylation of alcohols to aldehydes/ketones by direct β-C H elimination, as indicated by the IR result. The oxidation of different cycloalcohols showed that the activity increased with an increase in their methyl groups. Both conversion and ketone selectivity higher than 99% were achieved for cyclooctanol and cyclododecanol.

The layered silicate RUB-39 can be transformed by topotactic condensation into RUB-41 (RRO), a zeolite with 8- and 10- ring pores. If the layered RUB-39 is first silylated with dichlorodimethylsilane (DCDMS) or hexamethyldisiloxane (HMDS), an interlayer expanded structure is created after calcination. The DCDMS expanded material contains 10- and 12-ring pores instead of 8- and 10-ring pores. Detailed physicochemical characterization showed that the Al content is not significantly changed during the expansion. In the hydroconversion of decane, the expanded materials have a significantly increased activity, as demonstrated by the lower temperatures at which isomerization and cracking occur. Detailed comparison of the product selectivities obtained with RUB-41 or with its expanded analogs shows that the void structure of the expanded materials is significantly less constrained, as reflected in the distribution of methylnonane isomers, of the ethyloctane vs. methylnonane isomers, and in the ratio of monobranched vs. dibranched isomers.

Aluminum was incorporated into the layered silicate RUB-39, which is transformed by calcination into RUB-41. This new zeolite with RRO topology contains 8- and 10-ring pores, and the acid sites in the aluminated material catalyze the synthesis of methylamines, in particular mono- and dimethylamine, by amination of methanol. Owing to the shape-selective catalytic properties of (H)Al-RUB-41, low selectivity to the thermodynamically favored trimethylamine product is obtained in comparison with results on RUB-39 or non-shape-selective materials. Both activity and selectivity are highest for RUB-41 catalysts with a high Si to Al ratio. Silylation reduces the number of unselective sites and results in a further suppression of trimethylamine formation. The introduction of acidity in the intact RUB-41 structure is supported by Al-MAS NMR and NH3-TPD data. Additional characterization by XRD and SEM is provided.

H-Al-MWW with different Si/Al ratios has been synthesized in the presence of hexamethyleneimine by the postsynthesis method with the ion-exchange of Na + with NH 4 + unnecessary. However, irrespective of the framework Si/Al ratio, the as-synthesized Al-MWW lamellar precursor was not transformed into the Al-YNU-1 phase by the method used for preparing Ti-YNU-1 [W. Fan, P. Wu, S. Namaba, T. Tatsumi, Angew. Chem. Int. Ed. 43 (2004) 236]. This may be due to the difficulty in removing hardly oxidized hexamethyleneimine molecules by acid treatment, as shown by TG/DTA measurement results. In combination with 13 C CP/MAS NMR spectroscopy, it was indicated that these hardly oxidized hexamethyleneimine molecules might strongly interact with the zeolite framework or be tightly constrained between the layers. Nevertheless such a type of templating molecules could be washed away by acid when piperidine was used as a template. As a result, H-Al-YNU-1 with a pore opening intermediate between those of H-Al-MOR and H-Al-Beta was successfully prepared in the way adopted for preparing Ti-YNU-1. This material showed much higher activity than H-USY, H-Al-MOR, H-Al-Beta, H-Al-MWW, H-Al-ZSM-5, and interlayer-expanded H-Al-MWW through silylation in alkylation of anisole with benzyl alcohol and acylation of anisole with acetic anhydride as a result of its enlarged pore opening connected to supercages and predominant moderately strong Bronsted acid sites. The benefit of the large pore opening of H-Al-YNU-1 was also confirmed by the catalytic results obtained in the Baeyer–Villiger reaction of cyclohexanone with bulkiness corresponding to 12 membered-ring pore openings.

We investigated the influence of solvent on the activity, epoxide selectivity, and H2O2 efficiency of three types of zeolites—TS-1, Ti-Beta, and Ti-MWW—in the liquid-phase epoxidation of 1-hexene and cyclohexene. We found that the effect of solvent not only was related to the hydrophilicity/hydrophobicity of titanosilicates, but also was highly dependent on substrates. Acetonitrile should be the solvent of choice for the oxidation of 1-hexene over Ti-Beta and Ti-MWW, whereas methanol is preferred by TS-1. In contrast, for cyclohexene oxidation, methanol is favorable for Ti-Beta, whereas acetonitrile is the best for TS-1 and Ti-MWW. The effect of hydrophilicity/hydrophobicity is demonstrated by a series of catalytic results, but this cannot explain the solvent effect on the oxidation of cyclohexene over Ti-Beta. The H 2O2 efficiency depends strongly on the aprotic/protic nature and polarity of solvents, as well as on the properties of titanosilicates.

Cobalt-substituted polyoxometalate (POM), α -[SiW 9 O 37 {Co(H 2 O)} 3 ] 10− , was heterogenized for its effective use as a solid catalyst in the liquid-phase reaction by inserting it in between the layers of basic Mg 3 Al-hydrotalcite. It was characterized by FT-IR, UV–vis, X-ray diffraction, N 2 adsorption–desorption and elemental analysis. A POM cluster was intercalated into the interlayer of layered double hydroxide (LDH), and the integrity of the cluster [SiW 9 Co 3 ] was maintained when the hydrotalcite precursor, Mg 3 Al-LDH-carbonate, was transformed into a mixed-oxide solid solution, followed by the formation of Mg 3 Al-LDH-hydroxide through hydrolytic reconstruction and Mg 3 Al-LDH-adipate via anion exchange by organoacid precursor before its use in the pillaring reaction under a stringent N 2 atmosphere. The intercalated cobalt-substituted POM cluster showed high catalytic activity and reusability in the liquid-phase selective oxidation of cyclohexanol to cyclohexanone using 1 atmosphere of molecular oxygen under mild reaction conditions.

Mn-MgAl hydrotalcite, surface-enriched with Mn, was prepared by thermal decomposition of MgAl hydrotalcite followed by reconstruction of its structure in the presence of Mn(II) cations and atmospheric CO2 as a guest inorganic anion through contacting the decomposed mass with aqueous Mn(II) nitrate solution. The Mn-MgAl hydrotalcite showed very high catalytic activity, stability, and reusability in the liquid-phase selective oxidation of a wide range of alkylaromatics to their corresponding benzylic ketones, using atmospheric pressure of molecular O2 as a sole oxidant under solvent-free and mild reaction conditions. The catalytic performance of Mn-MgAl hydrotalcite was found to be much higher than that of Mn-containing hydrotalcites prepared by different methods or MgAl hydrotalcite catalysts containing various other transition metals and synthesized through similar procedures.

A new titanosilicate molecular sieve structurally analogous to MWW-type lamellar precursors (designated as Ti-YNU-1) was postsynthesized by adjusting the titanium content in the synthesis gel and washing the as-synthesized material with acid under refluxing conditions. The samples were characterized with XRD, ICP, TG/DTA, FTIR, UV–vis, and 29 Si MAS NMR techniques as well as N 2 , Ar, and H 2 O adsorption experiments. It was indicated that compared with Ti-MWW, Ti-YUN-1 had more silanols in the structure and that its interlayer spacing was expanded by nearly 2.5 A. In addition, the local environment of T 1 sites of the proposed structure of Ti-YNU-1 was also different from that of Ti-MWW. This led to a great increase in the pore openings connected to supercages. The formation of Ti-YNU-1 was highly dependent on the Si/Ti ratio in the synthesis gel and also might be related to the removal of about 80% templating molecules by acid treatment before calcination. Extensive evaluation of the catalytic performance of various titanosilicates for the oxidation of different cycloalkenes showed that Ti-YNU-1 behaved like a 12-membered ring (MR) zeolite. This is further confirmed by the results that a strong peak around 6.7 A was present in the pore size distribution curve obtained from Ar adsorption for the Ti-YNU-1 sample but absent in that for the Ti-MWW sample, and that cyclohexene conversion increased but 1-hexene conversion decreased with increasing Si/Ti ratio. Compared with the other titanosilicate materials, Ti-YNU-1 showed high activity, selectivity, and stability in the liquid-phase epoxidation of bulky cycloalkenes with H 2 O 2 as an oxidant. An investigation of the effect of several protic and aprotic solvents on the catalytic property of Ti-YNU-1 in the epoxidation of cyclohexene revealed that acetonitrile should be the solvent of choice considering both conversion and selectivity.

The liquid-phase ammoximation of cyclohexanone with ammonia and hydrogen peroxide was conducted over Ti-MWW. Ti-MWW is capable of giving both cyclohexanone conversion and oxime selectivity >99% under optimum reaction conditions. It is a highly active, selective, and reusable catalyst for the synthesis of cyclohexanone oxime in the presence of water. In comparison to other titanosilicates, Ti-MWW shows much higher catalytic activity, even superior to that of TS-1. The catalytic performance of Ti-MWW depends greatly on the operating conditions of the reaction, especially the method of adding substrates. The reason why the method of adding substrates plays such an important role in the ammoximation of ketones or aldehydes over Ti-MWW was investigated after a detailed evaluation of the reaction mechanism.

The effect of acid treatment on the catalytic performance of ultrastable Y catalysts in the Beckmann rearrangement of cyclohexanone oxime has been investigated under liquid phase conditions. Over the catalysts treated under mild conditions, enhanced activity was observed due to an increase in the amount of Bronsted acid sites, but a considerable amount of extra-framework aluminum (EFAL) with Lewis acidity remained, resulting in a rapid loss of selectivity to ɛ-caprolactam. Under relatively severe conditions, the extensive removal of EFAL improved the lactam selectivity, although the extraction of framework aluminum resulted in decreased oxime conversion. Pyridine and benzonitrile adsorption studies indicated the presence of at least two different kinds of Lewis acid sites in the catalysts. The relationships between the catalytic performance and Fourier transform infrared spectroscopy suggested that weak Bronsted acid sites are the active centers for the rearrangement reaction, whereas weak Lewis acid sites due to an extra-framework amorphous phase are responsible for the cyclohexanone formation. Thus the catalyst with weak Bronsted acid sites and a small amount of acidic EFAL species is active and selective for the liquid phase Beckmann rearrangement of cyclohexanone oxime.

The catalytic activity and selectivity of Ti-MWW in the epoxidation of diallyl ether (DAE) with hydrogen peroxide to allyl glycidyl ether (AGE) and diglycidyl ether (DGE) have been studied by a comparison with those of TS-1, and the issues concerning the consecutive reaction and the selective production of AGE have been considered. Ti-MWW catalyzed the DAE epoxidation in the presence of aprotic solvents such as acetonitrile or acetone, and produced only minor levels of solvolysis products. Ti-MWW proved to be a reusable catalyst standing up to the Ti leaching and maintaining the catalytic activity and the product selectivity in the reaction–regeneration cycles. Studies with different solvents, Ti contents, reaction times, temperature, and catalyst amounts confirmed that the DAE epoxidation was a typical consecutive reaction with AGE as an intermediate product and DGE as a secondary one. The reaction rate for AGE formation was much faster than that for DGE, making the selective production of AGE possible by controlling the reaction up to a DAE conversion level of ca. 30%.

A series of mesoporous molecular sieves with various SiO 2 /Al 2 O 3 ratios have been applied to the liquid-phase Beckmann rearrangement of cyclohexanone oxime. The influences of solvent, aluminum content, aluminum-incorporating method, and catalyst structure on the catalytic performance have been investigated. Benzonitrile has been found to be a suitable solvent. The surface silanol groups ineffectively catalyze the rearrangement, whereas the acid sites generated by incorporation of aluminum improve the activity and the selectivity to ɛ -caprolactam remarkably. Moreover, an Al-containing MCM-41 catalyst prepared by the postsynthetic method using AlCl 3 as an aluminum precursor exhibits higher lactam selectivity than a directly synthesized one. For a given aluminum content, MCM-41 shows superior performance to beta zeolite and other mesoporous catalysts, SBA-1 and SBA-15. It has been suggested that a sufficient amount of acid sites with appropriate strength is of importance to the liquid-phase Beckmann rearrangement.

Al- and Ga-incorporated ETS-10, designated as ETAlS-10 and ETGaS-10, respectively, were synthesized by using P25 titania as a Ti source. The isomorphous substitution of Al and Ga for framework Si at the (4Si) environment was confirmed by 29 Si MASNMR measurements. ETS-10 was more active in the Knoevenagel condensation than Y-type zeolites. The introduction of Al and Ga into ETS-10 enhanced the activity, due to the increase of the ion-exchange sites, which act as Bronsted base sites. The ion exchange of Na and K in ETS-10 for larger alkali cations such as Rb or Cs caused an increase in the activity for the Knoevenagel reaction of the less reactive and less bulky substrates. ETS-10 selectively promoted the Knoevenagel condensation product compared to homogeneous amine catalysts, which produced the undesired self-condensed products of active methylene compounds.

Highly effective formation of cyclopentanol through the liquid-phase hydration of cyclopentene has been attempted on various zeolites catalysts. MCM-22 zeolite was the most selective catalyst, which actively converted cyclopentene to cyclopentanol with a selectivity up to 99%. The effects on the hydration of catalyst preparation method, reaction atmosphere and temperature have been investigated for the MCM-22 catalysts. On the basis of the effect of reaction atmosphere, the mechanism of liquid-phase cyclopentene hydration was proposed. The thermodynamic equilibrium between cyclopentene and cyclopentanol was suggested to control greatly the cyclopentene conversion. The cyclopentene conversion was increased to 10% by increasing the water/cyclopentene ratio. Poisoning using organic amines with different molecular sizes revealed that the hydration occurred mainly in the 10-membered ring channels of MWW structure, which had an elliptic aperture smaller than that of MFI structure, exhibiting a significant shape selectivity by suppressing the etherification cyclopentanol.

The epoxidation and successive pinacol formation of tri- and tetraalkyl-substituted olefins using Ti-β/H 2 O 2 /H 2 O as the catalytic system has been investigated. Aluminum-free Ti-β exhibits better activity and pinacol selectivity than TS-1, TS-2, Ti–MCM-22, and mesoporous Ti–MCM-41. Pinacol ( vic -diol) is obtained as the major product with small amounts of the side products pinacolone, alcohol (via hydration), and oligomers. The conversion and pinacol selectivity increase with an increase in reaction temperature and time. The change in product distribution with reaction time over Ti-β shows that the epoxide is the initial product which undergoes a secondary reaction to give pinacol as the major product. The conversion and H 2 O 2 selectivity decrease with the bulkiness of the substituents at the C C bond but the selectivity of pinacol is not significantly affected. The reactivity of cyclic 1-methyl-1-cyclohexene is considerably lower than that of the corresponding open-chain analogue 2-methyl-2-butene. The symmetrical tetramethyl-substituted 2,3-dimethyl-2-butene led to the formation of small amount of dimers over medium-pore titanium silicates TS-1, TS-2, and Ti–MCM-22. The epoxidation of these substituted olefins proceeded more rapidly when using acetonitrile as a cosolvent than under triphase conditions. Mechanistically, the primary epoxide product undergoes acid-catalyzed nucleophilic ring opening by H 2 O molecules to give pinacol.

The epoxidation of a variety of electron-deficient α,β-unsaturated carbonyl compounds has been studied using dilute H 2 O 2 and titanium-containing zeolites under liquid-phase conditions. The influence of the reaction medium and the structure of titanium-containing silicates (Ti-β(OH), Ti-Al-β(OH), Ti-β(F), TS-1, TS-2, Ti-MCM-22, and Ti-MCM-41) have been investigated. The weak basic acetonitrile solvent shows better activity and selectivity for epoxide than for other solvents used in this reaction over large-pore zeolite Ti-β. Among the various titanosilicates studied, aluminum-free Ti-β exhibits the best activity and H 2 O 2 selectivity for cyclic α,β-unsaturated ketone, whereas Ti-β and TS-1 exhibit similar activities for open-chain α,β-unsaturated carbonyl compounds. The medium-pore TS-1, TS-2, and Ti-MCM-22 exhibit lower activities for the oxidation of cyclic ketones due to their diffusion limitation. For unsaturated ketones, epoxides are selectively formed, whereas unsaturated aldehydes mainly produce carboxylic acid. Branching at α- and/or β-carbon influences the reactivity of the carbonyl compounds considerably. However, the Ti-β/H 2 O 2 catalytic system fails to oxidize substrates like α,β-unsaturated acids, α,β-unsaturated esters, and isophorone.

The catalytic properties of Ti–MWW catalysts have been studied for the oxidation of alkenes using hydrogen peroxide or tert -butyl hydroperoxide (TBHP) as an oxidant. Ti–MWW shows superior activity independent of the nature of oxidant when compared to the other Ti-containing catalysts both of microporous TS-1 and Ti-MOR and of mesoporous Ti–MCM-41 in the oxidation of cyclohexene. Compared to large-pore Ti–Beta, Ti–MWW is less active than in the oxidation of cyclohexene using H 2 O 2 , but its shows comparable activity in the case of TBHP. Ti–MWW is very stable in both the structure and the states of Ti species in the actual cycle of reaction–regeneration. The framework B species remaining within the Ti–MWW catalysts seem to have little influence on the intrinsic activity of framework Ti species, but they act as Bronsted acid sites contributing to the hydrolysis of the oxide product to form glycols. The turnover number (TON) of Ti–MWW for the cyclohexene conversion decreases sharply with increasing Ti content, while the TON for the 1-hexene conversion shows volcanic behavior when related to the Ti content. It is clarified that the bulky reaction is catalyzed mainly by the Ti species within the supercages and the exterior pockets of the MWW structure, while in addition to these highly accessible Ti species, those within the channels of a 10-membered ring greatly contribute to the oxidation reactions not significantly sizedemanding.

Highly ordered, titanium-rich organically modified Ti-MCM-41 materials have been synthesized at 413 K using a mixture of organo-triethoxysilane and tetraethyl orthosilicate. Various organic substituents on Ti-MCM-41 used in the present study are methyl, vinyl, allyl, 3-chloropropyl, pentyl, and phenyl. The highest amount of Ti incorporated for a given Si/Ti mole ratio of 30 in the synthesis gel was 33.6 in the case of the 3-chloropropyl group. For methyl, vinyl, allyl, pentyl, and phenyl this ratio varied from 42 to 53, which is considerably lower than for unmodified Ti-MCM-41 reported earlier. Whereas incorporation of short chain organic functionality (C1–C3) causes an increase in the d spacing, resulting in wider pore openings, long chain (pentyl) and aromatic (phenyl) substituents cause a decrease in d spacing in these mesoporous molecular sieves. An increase in the organic content in the synthesis gel beyond a certain level also causes a decrease in d spacing. N2 and H2O adsorption studies revealed that these organically modified well ordered Ti-MCM-41 materials are more hydrophobic than that synthesized in the absence of organic modifiers. These organically modified Ti-MCM-41 materials are efficient catalysts in the epoxidation reaction of unsaturated alcohols followed by cyclization to cyclic ethers using TBHP as oxidant.

Molybdenum sulfide cluster [Mo 3 S 4 (H 2 O) 9 ] 4+ and nickel–molybdenum bimetallic sulfide cluster [Mo 3 NiS 4 Cl(H 2 O) 9 ] 3+ were incorporated into zeolites NaY, HUSY, NaHβ, Na-mordenite (NaMOR), and KL by aqueous ion exchange. EXAFS data revealed that the structure of the molybdenum sulfide cluster remained virtually intact after ion exchange. However, the incomplete cubane-type structure of the cluster might be lost after thermal treatment at 573 K. The structure of the cluster in Mo 3 S 4 /NaY and Mo 3 S 4 /KL seems to have changed to the MoS 2 -like structure through the hydrodesulfurization (HDS) reaction, although a considerably high level of dispersion was kept. Mo 3 S 4 cluster catalysts loaded on NaMOR and KL exhibited a higher level of activity for HDS of benzothiophene than Mo 3 S 4 catalysts loaded on the other zeolites. Benzene was formed through acid-catalyzed dealkylation of ethylbenzene, the primary HDS product. Alkylation of benzothiophene with alkenes derived from the cracking of decane as the solvent also occurred. The acidity seems to be produced through the ion exchange and reduction of cationic clusters during activation. Over HUSY- and NaHβ-supported catalysts benzene was the major HDS product. Nickel incorporation into the Mo 3 S 4 zeolite catalysts remarkably enhanced the HDS activity. Introduction of the Mo 3 NiS 4 core into zeolite as a precursor resulted in catalysts with higher HDS activity than that of Mo 3 S 4 core and Ni 2+ independently; it is conceivable that the intimate interaction between nickel and molybdenum in the precursor is effective at producing active species.

Open chain unsaturated alcohols 1 , having the general formulaR1R2C=CH(CH2)nCR1R2OH (whereR1,R2=H or CH3, andn=1–3) and carbocyclic unsaturated alcohols of similar type have been efficiently cyclized to the corresponding hydroxytetrahydrofuran or hydroxytetrahydropyran over titanium silicate molecular sieves (TS-1 and Ti-beta), in one pot under mild liquid phase reaction conditions using dilute hydrogen peroxide as oxidant. When the hydroxy nucleophile may attack either of the activated carbon atoms of the epoxides generatedin situ, to lead to a derivative of tetrahydrofuran or tetrahydropyran, the former exclusively formed. The regioselectively for such reaction is 100%. WhenR1orR2=CH3, among the diasteroisomeric productstranspredominates overcis. In this cyclization reaction titanium silicate epoxidizes the olefin and successively catalyzes the opening of the oxirane ring via intramolecular attack of hydroxy oxygen. Thus the behavior of titanium sites is bifunctional in nature. However, for bicyclic unsaturated alcohols, because of geometric restriction, activity of medium pore TS-1 is very low. Ti-beta synthesized by dry gel conversion has been found to be an efficient catalyst in oxidative cyclization of such bulky organic substrates as α-terpineol, isopulegol, andtrans-p-menth-6-ene-2,8-diol to their corresponding tetrahydrofuranols or tetrahydropyranols with a very high regioselectivity.

Ti-beta zeolite was synthesized in the presence of sodium cations by a dry-gel conversion method using tetraethylammonium hydroxide as a structure-directing agent. As evidenced by diffuse reflectance UV spectroscopy, incorporated titianium species were tetrahedrally coordinated in the zeolites and neither anatase-like phase nor hexacoordinated titianium species belonging to an amorphous titanosilicate phase was detected at the sodium content of lower than 1.0 mol%. It was found that the Ti-beta catalysts gave very high H2O2conversion and selectivity in the oxidation of cyclohexene in methanol used as solvent. The C6-C8cyclic alkenes and alkanes reacted faster than corresponding linear alkenes and alkanes, showing the lack of steric impediments in the pores of Ti-beta. Dimethylcyclohexanes were more reactive when tertiary H atoms predominantly occupy the equatorial position than when they occupy the axial position. Ti-beta samples exhibited high activity also for the oxidation of C6-C8cyclic alcohols.

Titanium silicate molecular sieve, TS-1, has been found to be a highly efficient and selective catalyst in dihydroxylation of olefins under triphase reaction conditions in the presence of dilute hydrogen peroxide. Among the substrates unsaturated alcohols (≧C4) give selectively corresponding triol in a very high yield with very high H2O2efficiency. Unsaturated halides give the corresponding diols even at a faster reaction rate. Whereas under the conventional biphase system (in the presence of a cosolvent to homogenize the liquid layers) epoxide is obtained as the major final product in high yield. The substrate nature, i.e., steric hindrance at the active site and hydrophobicity/hydrophilicity of both substrate and epoxide intermediate, is considered to account for the product distribution. Acidity generatedin situover TS-1 in the presence of water (used as the dispersion medium) is responsible for the bifunctional (oxidation and acidic) behavior of the titanium silicate.

Ammoximation of cyclic ketones on TS-1 and amorphous SiO2–TiO2with H2O2and NH3was studied. The reactivity of cyclicketones over TS-1 and amorphous SiO2–TiO2showed the following order: cycloheptanone > cyclopentanone > cyclohexanone > cyclooctanone. Shape-selective poisoning studies revealed that the active sites of TS-1 for ammoximation of cycloheptanone are mostly inside the molecular sieve. The reactivity of cyclohexanone and methylcyclohexanones over TS-1 followed the order cyclohexanone > 2-methylcyclohexanone = 3-methylcyclohexanone > 2,6-dimethylcyclohexanone, reflecting the difference in the diffusivity among the reactants or products inside TS-1. Besides the diffusivity the reactivity seemed to be affected by the difficulty in access of the carbonyl group to the Ti active site inside the zeolite; from the comparison of reactivity of dimethycyclohexanone isomers, the steric hindrance of the substituent methyl group to the access of carbonyl group was considered to decrease in the following order: β-equatorial > α-equatorial > β-axial > α-axial. Diffusion of cyclohexanone or its oxime has been found to play an important role in the ammoximation when the TS-1 crystals larger than 1.5 μm were employed as a catalyst. For the TS-1 crystals smaller than 0.3 μm, the ammoximation activity was independent of the diffusivity factor and was determined by the number of active Ti sites present in the zeolite framework.

The influence of the method for loading platinum precursor and adding KCl, KCl loading content, calcination temperature, KCl addition procedure, various additives, and water washing on the activity and selectivity of Pt/KL catalysts for hexane reforming reaction has been investigated. The catalyst preparation methods involve ion exchange (IE), incipient wetness impregnation (IWI), and coimpregnation with KCl (IWI-KCl). The Pt/KL catalysts prepared by ion exchange with [Pt(NH3)4]Cl2 followed by impregnation with KCl (IE-KCl) gave much higher activity and selectivity for benzene formation than the catalysts prepared by coimpregnation of KL zeolite with [Pt(NH3)4]Cl2 and KCl. The IE-KCl catalyst with KCl/Pt molar ratio of 4.5 showed 100.0% conversion of hexane and 89.3% yield of benzene at 743 K and 0.2 MPa. The IE-KCl catalysts exhibited lower H/Pt ratios than the IE catalyst. The KCl addition procedures markedly affected the activity and selectivity of the Pt/KL catalyst; the addition of KCl to the IE sample prior to calcination and reduction was necessary for the catalyst to exhibit the high activity in benzene formation. It has also been found that the performance of Pt/KL catalysts is markedly affected by the calcination temperature. With the IE-KCl catalysts, however, the decrease in the benzene yield caused by high-temperature calcination was not as serious as with the IE catalyst. In contrast, with the IWI and IWI-KCl catalysts, the activity for benzene production was highly sensitive to the calcination at high temperature, drastically decreasing by calcination at 823 K. The Cl species on the IE-KCl catalysts may have existed in the state of KCl.

Methanol synthesis activity of palladium supported on four types of silica (Davison 01, 03, 57, and 59) were evaluated at 16 atm and 255 °C in a Berty-type reactor. Turnover frequencies (TOF) were determined based on hydrogen chemisorption data. The TOF's for a particular type of silica increased with decreasing metal dispersion, but for equivalent dispersions the silicas had a marked effect, with TOF's following the sequence Pd SiO 2 (59)> Pd SiO 2 (57)> Pd SiO 2 (01,03). Preliminary results on unsupported Pd show that the activity was less than expected on the basis of particle size. Thus, the silica promotes the activity of the Pd, even though the supported metal particles are relatively large and the TOF increases with particle size. Chloride ions enhance activity by stabilizing higher dispersions and by increasing TOF's. Lithium ions effect extensive sintering of the silica support and promote activity by increasing the TOF. The latter increase may, in part, be the result of more efficient use of Pd surface which occurs via the exclusion of small pores. The more active Pd SiO 2 catalysts were found to be comparable in activity to a commercial methanol synthesis catalyst.

The addition of probe molecules, such as ethylene, propylene, methanol, ethanol, and acetaldehyde, to COH2 feed was studied over the KCl-promoted and the unpromoted MoSiO2 catalyst under synthetic conditions, in order to clarify the reaction paths for the formation of hydrocarbons and alcohols. The results of olefin addition study suggest that the alcohol formation from COH2 proceeds by a mechanism including steps identical with those in the hydrocarbonylation of olefins and that KCl suppresses the simple hydrogenation of olefins. Both of the Mo catalysts demonstrate a poor catalytic activity for the homologation of methanol to ethanol. Alcohol homologation seems to be only a minor process in the formation of C+2 alcohols. No significant activity of Mo catalysts for incorporation of acetaldehyde into C3 oxygenated compounds may exclude the intermediacy of aldehydes for the chain growth of alcohols. Hydrogenation of acetaldehyde to ethanol is the fast and predominant reaction, in agreement with the fact that alcohols compose more than 90% of the organic oxygenates produced from COH2. Aldol condensation is apparently unimportant for the chain growth. The contribution of alcohol dehydration to hydrocarbon formation may be insignificant over the KCl-promoted catalyst with KMo = 0.4. Consequently, a mechanism including CO insertion into the alkyl-metal bond is proposed for the main reaction path for the higher alcohol formation from COH2. The role of K is supposed to slow the hydrogenation of surface alkyl species to form alkanes as well as to increase the active sites for alcohol formation by retarding the reduction of Mo.

The selective production of C/sub 2//sup +/ alcohols from CO and H/sub 2/ is of both commercial and academic interest in C/sub 1/ chemistry. The alcohol mixtures can be used as additives in gasoline to enhance the octane number. There are a number of reports on the catalysts for the synthesis of light alcohols. Synthesis of alcohols on molybdenum-based catalysts, however, was not reported until the authors discovery that mixed alcohols were efficiently produced from CO and H/sub 2/ on alkali-promoted molybdenum catalysts. Other interesting features of Mo catalysts were that they operated well in a CO-rich gas and are resistant to sulfur poisoning. In the initial study in this laboratory, catalysts were prepared by coimpregnation of SiO/sub 2/ with KCl and Mo salts. As the Mo loading was decreased, however, the authors encountered a difficulty in preparing the catalyst with good reproducibility. Hence they have employed different preparations for the Mo-K/SiO/sub 2/ catalysts. In this note they report that sequence of impregnation greatly affects the activity and selectivity. A sequence in which the K is added first, followed by impregnation with (NH/sub 4/)/sub 6/Mo/sub 7/O/sub 24/, gives rise to reproducible preparation of catalysts for alcohol production. 26 references.