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Abstract: SBA-15, grafted with Lewis acidic Ti4+ ions and basic amines (imidazole, guanine or adenine) exhibited high catalytic activity in the cycloaddition of CO2 to epoxides yielding selectively cyclic carbonate precursors of polycarbonates. In the second class of materials, the surface of SBA-15 was grafted with thiol or sulfonic acid functionalities. Mn(Salen)Cl was, then, covalently bound to these acidic groups. The resulting catalysts show enhanced chemo-, regio- and stereo-selective catalytic activity in the epoxidation of terpenes such as R-(+)-limonene, α-pinene and Δ-carene with molecular oxygen. The acid–base properties of these modified SBA-15 materials were investigated by temperature-programmed desorption and diffuse-reflectance infrared Fourier transform spectroscopy. Ammonia and pyridine were used as probe molecules for acidic sites and CO2 for basic sites. Acidic Ti sites activated epoxides and the grafted basic amines activated CO2. The simultaneous presence of both acidic and basic sites on amine/adenine-functionalized Ti-SBA-15 enabled synergistic enhancement in catalytic activity in the cycloaddition reaction of CO2 to epoxides. When Mn(Salen)Cl was immobilized on thiol or sulfonic acid-functionalized SBA-15, the oxidation state of Mn decreased from +3 to +2. The organo-acidic functional groups (thiol or sulfonic acid) axially coordinated to Mn ions modified the electronic structure of Mn ions enhancing the activity and selectivity of Mn(Salen) complexes in aerial oxidation reactions. [Copyright &y& Elsevier]

Preferential oxidation (PROX) of CO in hydrogen-rich steam reformates was investigated using CuO–CeO2, CuO–CeO2–ZrO2, and CuO–ZrO2 catalysts. CuO (1–10 wt%) samples supported over high-surface-area (SBET=117–172 m2/g), cubic CeO2, CeO2–ZrO2, and ZrO2 were synthesized by coprecipitation. The composition of the support markedly influenced the PROX activity. Both CuO–CeO2 and CuO–CeO2–ZrO2 exhibited higher activity and selectivity in CO oxidation than CuO–ZrO2. The adverse influence of H2O was accentuated in catalysts containing ZrO2. Below 423 K and over CuO–CeO2 with less than 5 wt% CuO, the presence of H2O in the feed suppressed CO oxidation. H2O had a negligible effect on H2 oxidation. The catalysts showed stable activity in long-term experiments with the realistic feeds. The catalysts were characterized by XRD, surface area, TPR, diffuse reflectance UV–visible, EPR, and magnetic-susceptibility techniques. While a small amount of copper might be incorporated in the CeO2/ZrO2 fluorite lattice (forming a solid solution), most of it was at the surface of the support as isolated monomeric (types I and II) and dimeric (type IV) copper oxo species, nano-sized copper clusters containing magnetically interacting copper ions (type III) and a CuO-like, bulk phase. While the isolated copper oxo species exhibited reversible reduction–oxidation behavior, the interacting copper and CuO-like phases exhibited irreversible reduction behavior. The amount and reducibility of CuO on different supports correlated with their CO oxidation activities and increased in the order CuO–ZrO2⩽CuO–CeO2–ZrO2. [Copyright &y& Elsevier]

Abstract: Solid Fe-Zn double-metal cyanide (DMC) complexes exhibit high catalytic activity for hydrolysis of edible and non-edible vegetable oils and animal fat. In a batch reaction, complete conversion of vegetable oil triglycerides to fatty acids with selectivity greater than 73wt% was obtained at temperatures as low as 463K, autogenous pressure and with 5wt% of catalyst. Catalytic activity of DMC was superior to Amberlyst™70, SAPO-11, H-β, HY, MoO x /Al2O3 and sulfated zirconia. Rates of hydrolysis were greatly enhanced when solvents (tetrahydrofuran or N,N-dimethylformamide), phase transfer agents (tetrapropyl ammonium bromide) and products (a mixture of mono-/diglycerides and fatty acids) or fatty acid was added to the feed. Surface hydrophobicity which enables high wettability and activation of glycerides on active, acidic sites of reusable DMC is attributed to be the major cause for its superior catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: Fe–Zn double-metal cyanide complexes are currently used as catalysts for the ring-opening polymerization of epoxides, as well as the coupling of epoxides and CO2 for the production of polycarbonates. We report their novel application as highly efficient solid catalysts for the transesterification reactions of carbonates. The catalysts were prepared from aqueous solutions of ZnCl2 and K4Fe(CN)6 in the presence of tert-butanol (complexing agent) and tri-block copolymer EO20PO70EO20 (average molecular weight, 5800; co-complexing agent). They were characterized by chemical analysis, XRD, thermal analysis, N2 adsorption, magnetic susceptibility, SEM, and FTIR, diffuse reflectance UV–visible, EPR, and X-ray photoelectron spectroscopies. Their acidity was determined from the IR spectra of adsorbed pyridine and the temperature-programmed desorption of NH3. Catalyst samples prepared with both complexing and co-complexing agents were found to be more acidic and catalytically active than those prepared without these agents. These catalysts are more active/selective than other solid catalysts hitherto reported. Dimethyl carbonate, for example, could be synthesized with 100% selectivity and an isolated yield of >86% by the reaction of propene carbonate with methanol. The catalysts can be recycled without significant loss in activity. Lewis acidic Zn ions are the possible active sites for the transesterification reaction. [Copyright &y& Elsevier]

Abstract: As-synthesized MCM-41 was used as a reusable, heterogeneous catalyst for the eco-friendly synthesis of cyclic carbonate precursors of polycarbonates via a cycloaddition reaction of CO2 with epoxides. This catalyst is also efficient for the synthesis of alkyl and aryl carbamate precursors of polyurethanes via the reaction of amines, CO2 and alkyl halides. Both these reactions were carried out under mild conditions and without using any solvent or co-catalyst. CO2 is utilized as a raw material replacement for toxic phosgene in the conventional synthesis of these chemicals. [Copyright &y& Elsevier]

Abstract: 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 1446cm−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 1609cm−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 473K 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. [Copyright &y& Elsevier]

Abstract: As-synthesized zeolite-beta exhibits high catalytic activity for the synthesis of cyclic carbonates and alkyl and aryl carbamates by a phosgene-free route, utilizing the greenhouse effect gas CO2. The reaction occurs with high yields of the desired products at mild conditions and without using any solvent or cocatalyst. Cyclic carbonates are synthesized by cycloaddition reaction of CO2 with oxiranes (epichlorohydrin, propene oxide, styrene oxide and n-butene oxide) at 393K and 6.9bar. Alkyl and aryl carbamates are synthesized by the reaction of the corresponding amines, CO2 and n-butyl bromide at 353K and 3.4bar. The as-synthesized zeolite-beta containing the encapsulated quaternary ammonium ions is not only reusable in several recycling experiments, but also shows superior activity to that of the corresponding homogeneous, quaternary ammonium halide salt generally used in the commercial synthetic practice. The microporous silica (inorganic) acting in concert with the encapsulated organic component constitutes an efficient, recyclable catalyst for this reaction. [Copyright &y& Elsevier]

Abstract: Cyclic carbonates were synthesized by the cycloaddition of CO2 to epoxides (epichlorohydrin, propene oxide, and styrene oxide), and carbamates were synthesized by reaction of alkyl or aryl amines, CO2, and n-butyl bromide. Solvents and cocatalysts/promoters like N,N-dimethylaminopyridine (DMAP) and quaternary ammonium salts, which are usually essential with conventional catalyst systems, could be avoided with the use of adenine-modified Ti-SBA-15 catalysts. The catalysts were reused in several recycle experiments. The structural and textural properties of the catalysts were determined by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption, and Fourier transform infrared (FTIR) and diffuse reflectance ultraviolet–visible (UV–vis DRS) techniques. Acid–base properties of the solid catalysts were investigated by temperature-programmed desorption (TPD) of NH3 and CO2 and DRIFTIR spectroscopy of adsorbed pyridine and CO2 techniques. The studies reveal that the Ti4+ ions increase catalytic activity by enhancing the adsorption of the epoxide and alkyl or aryl amine substrates. CO2 molecules are activated at the basic nitrogen groups of adenine. Increasing the surface concentrations of either CO2 (by anchoring basic molecules like adenine or increasing the partial pressure of CO2) or epoxides and alkyl or aryl amines (by increasing the concentration of Lewis acidic Ti4+ ions) enhances the catalytic activity. CO2 molecules activated at the covalently anchored adenine sites react with epoxide/amines adsorbed on the silica surface to form carbonates/carbamates. [Copyright &y& Elsevier]

Titanosilicate molecular sieves (TS-1, Ti-MCM-41 and amorphous TiO2–SiO2) catalyze transesterification reactions. Acidity measurements (pyridine adsorption-IR and NH3-TPD) reveal the presence of only weak Lewis acid sites. Catalytic activity parallels the acid strength and increases in the order: TS-1 < Ti-MCM-41 < amorphous TiO2–SiO2. TS-1 efficiently catalyzes the transesterification of only linear esters (ethylacetoacetate and diethylmalonate), but fails for cyclic esters like propylene carbonate. Ti-MCM-41 and amorphous TiO2–SiO2 are superior for the latter. The catalysts could be recycled without any loss in activity/selectivity. [Copyright &y& Elsevier]

A novel catalytic application of titanosilicate molecular sieves (TS-1 and TiMCM-41), in the synthesis of polycarbonate precursors like cyclic carbonates and dimethyl and diphenyl carbonates, avoiding toxic chemicals like phosgene or CO, is reported. Cyclic carbonates were prepared, over TS-1 and TiMCM-41, in high yields, by cycloaddition of CO2 to epoxides, like epichlorohydrin, propylene oxide and styrene oxide, at low temperatures and pressures. Further, transesterification of the cyclic carbonates with methanol and phenol, over TiMCM-41, yielded other polycarbonate precursors like dimethyl carbonate (DMC) and diphenyl carbonate (DPC). The cyclic carbonates could also be synthesized from the olefins in the same reactor by reacting the olefins, in the presence of TiMCM-41, with a mixture of an epoxidizing agent (like H2O2 or tert-butyl hydroperoxide) and CO2. [ABSTRACT FROM AUTHOR]

μ3-Oxo-bridged Co/Mn cluster complexes, CoMn2(O), exhibit high catalytic activity and selectivity for the aerial oxidation, in the homogeneous liquid phase, of cyclohexane, cyclohexanol, and cyclohexanone to adipic acid by a non-HNO3 route. The cluster complexes are superior to the individual Co and Mn acetates. The yields of adipic acid are comparable to those in the current processes using HNO3. Electron paramagnetic resonance and electronic spectra indicate that the cluster complex is probably decomposed during the reaction process. Attempts to use these cluster complexes encapsulated in zeolite–Y as solid catalysts for the oxidation reactions were unsuccessful due to significant leaching out of the complexes during the reaction. [Copyright &y& Elsevier]

TiOx, VOx, MoOx and WOx supported on SBA-15 exhibit efficient catalytic activity for oxyhalogenation of aromatics with the H2O2-halide ion system. Unlike the hitherto known solid catalysts, these reusable catalysts yield the para-halogenated product with 100% selectivity at 298 K and moderate acidic pH (3–5). The catalytic activity was enhanced by five orders of magnitude when supported on SBA-15. TiOx, VOx, MoOx and WOx supported on SBA-15 exhibit high catalytic activity for regiospecific oxyhalogenation of aromatics with the H2O2-halide ion system. The reaction occurs at 298 K and moderate acidic pH (3–5). The catalytic activity of these catalysts is higher than most of the hitherto known solid catalysts and unsupported metal oxides.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel application of Fe–Zn double metal cyanide complexes as solid, acid catalysts for regioselective synthesis of β-amino alcohols under solvent-free conditions via ring-opening of epoxides with amines is reported for the first time. The conversion of epoxides to β-amino alcohols is nearly 100%. In the reaction with styrene oxide, regioselective β-amino alcohol formation is higher with aromatic than with aliphatic amines. Strong Lewis acidic Zn2+ ions in the catalyst are probably the active sites in this reaction. [ABSTRACT FROM AUTHOR]

The aminolysis of epoxides over novel solid catalysts (Brönsted-acidic SBA-15 functionalized with propylsulfonic acid and Lewis-acidic Ti-MCM-41) is reported. The acidic properties of these catalysts were determined by FTIR spectroscopy and temperature-programmed desorption of pyridine and NH3, respectively. The mesoporous solid acids of the present study are reusable and exhibit significantly higher catalytic activities than known catalysts for opening of the oxirane ring with nitrogen (aromatic and aliphatic amines)-containing and oxygen (alcohols)-containing nucleophiles. A range of β-amino alcohols with high regioselectivity and stereoselectivity were synthesized. Adsorption studies as well as the sigmoid shape of the conversion-versus-time plots show that the epoxide and amine compete for adsorption on the acidic sites (-SO3H or Ti4+) on the catalyst surface. Epoxide adsorption and activation on acid sites are the more critical processes. Catalytic activity decreases with increasing basicity of the amines and/or the alcohol, as well as the dielectric constant of the solvent. [Copyright &y& Elsevier]

Abstract: A novel application of titanosilicate molecular sieves in the synthesis of β-amino alcohols via aminolysis of epoxides, at mild and solvent-free conditions, is reported, for the first time. A range of β-amino alcohols with nearly 100% regio- and stereoselectivity was produced over these reusable solid catalysts in high yields. [Copyright &y& Elsevier]

Abstract: A novel application of Fe–Zn double-metal cyanide (DMC) complexes as solid catalysts in the preparation of fatty acid alkyl esters (biodiesel/biolubricants) from vegetable oils is reported. The catalysts are hydrophobic (no H2O adsorption at reaction temperatures) and contain only Lewis acidic sites (NH3 and pyridine adsorption). Brönsted acid sites are absent (absence of 1546 and 1639cm−1 bands on adsorption of pyridine). Basic sites are also absent (no CO2 adsorption). Unlike the homogeneous or other solid catalysts (like ZnO–Al2O3, for example), the Fe–Zn, DMC catalysts are highly active even for the simultaneous transesterification of triglycerides and esterification of the free fatty acids (FFA) present in unrefined and waste cooking oils as well as non-edible oils. They are also tolerant of water, probably, due to their surface hydrophobicity. A relationship between the transesterification activity and the concentration of strong Lewis acid sites has been observed. Coordinatively unsaturated Zn2+ ions in the structure of the Fe–Zn complex are the probable active sites. [Copyright &y& Elsevier]

Alkyl and aryl carbamates are synthesized in high yields (≥80%) at mild reaction conditions by reaction of the corresponding amine, CO2 and alkyl halides over either titanosilicate molecular sieves or metal phthalocyanine complexes encapsulated in zeolite-Y. The catalysts could be reused with little or no loss in activity. In contrast to hitherto known catalysts for carbamate synthesis, the zeolite-based catalysts of the present study do not require additional onium salts as co-catalysts. [ABSTRACT FROM AUTHOR]

The structure of the reactive oxo-titanium species (hydroperoxo-, peroxo-, and superoxo-titanium) in titanosilicate molecular sieves (TS-1, Ti-β, amorphous Ti–SiO2, and TiMCM-41), generated on interaction with aqueous H2O2 or urea–H2O2 adducts, was investigated by electron paramagnetic resonance (EPR) and diffuse reflectance UV–visible (DRUV–visible) spectroscopies and magnetic susceptibility measurements. Two types of superoxo-titanium species (A and B) were identified in TS-1 and amorphous Ti–SiO2. An additional oxo species, A′, was also detected over Ti-β. TiMCM-41 generated, mainly, the B-type species. DRUV–visible spectroscopy and magnetic susceptibility measurements suggest the coexistence of both the superoxo- and hydroperoxo-titanium species. The A-type oxo-titanium species originate from the framework Ti sites having a tetrapodal (SiO)4Ti structure located inside the pores, while the B-type species originate predominantly from tripodal (SiO)3Ti(OH) structures, also located in the framework, probably at the external surface. The local structural environment of the Ti4+ ions, solvent, and temperature influence the concentration of these oxo-titanium species. The concentration of the A-type species decreased in the order: TS-1>Ti-β>amorphous Ti–SiO2. The B type varied as follows: TiMCM-41>amorphous Ti–SiO2>Ti-β>TS-1. In the oxidation of styrene, the A-type species correlate with styrene oxide formation, while the presence of B-type species lead to nonselective products. Experimental evidence is given for the involvement of the hydroperoxo-titanium species in olefinic epoxidations (styrene to styrene oxide) and the superoxo-titanium in aromatic hydroxylations (phenol to hydroquinone and catechol). [Copyright &y& Elsevier]

The influence of Ce/Zr ratio on the redox behavior of Ni in a series of NiO-CeO2-ZrO2 catalysts was investigated using in situ electron paramagnetic resonance (EPR), diffuse reflectance UV-visible (DRUV-visible) and X-ray photoelectron spectroscopy (XPS). At all concentrations, a small amount of Ni (species I) substitutes in the fluorite lattice. Superparamagnetic, nanosize Ni crystallites (species II) were found in samples with 1–5 wt.% NiO and ferromagnetic, larger Ni crystallites (species III) were detected in samples with 20 wt.% or more NiO when contacted with hydrogen. Ce promoted the reduction of Ni. The reducibility of Ni decreased in the order: I>III>II. At steam reforming conditions (in the presence of H2+H2O+hydrocarbon/alcohol at 773 K), the extent of Ni reduction varies in the order: H2+alkane>H2+alcohol>H2 alone. Catalytic activity and especially stability in the steam reforming of bio-ethanol (containing 5 ppm S) correlates with the type III Ni species and is influenced by both the Ni-content and the Ce/Zr ratio in the support. A catalyst of composition NiO (40 wt.%)-CeO2 (30 wt.%)-ZrO2 (30 wt.%) maintained its activity for more than 500 h without deactivation. [Copyright &y& Elsevier]

In an attempt to rationalize the differences in the catalytic behavior of titanosilicate molecular sieves when using H2O2 (TS-1, TiMCM-41) versus H2+O2 (Pd–TS-1) as oxidant, the Ti(IV)–superoxo and hydroperoxo/peroxo species formed in situ during the oxidation reactions were investigated by electron paramagnetic resonance (EPR) and diffuse reflectance UV–visible spectroscopies. Two types of superoxo species, A and B, were identified in TS-1; only the latter species was detected in TiMCM-41. EPR has provided evidence, for the first time, for the in situ generation of similar oxo species in reactions using H2+O2 instead of H2O2. The Ti sites adjacent to Pd ions (in Pd–TS-1) behave differently magnetically than the other Ti ions, generating a greater variety of superoxo species (A′, A″, A, B′, B, and C) and corresponding reaction products. Pd enhances the reducibility of Ti and promotes formation of these oxo species at lower temperatures (∼ 323 K). The epoxide selectivity in the oxidation of allyl alcohol over Pd–TS-1 is higher when using (H2+O2) than when using H2O2. In all cases, type A species predominantly catalyze epoxidations while type B favor the hydroxylations. The selectivity for epoxidation (vis-a&grave;-vis allylic oxidation) over these catalysts can be enhanced by controlling the type of Ti–oxo species formed in situ during the oxidation process by a suitable combination of catalyst, oxidant, solvent, and temperature. [Copyright &y& Elsevier]