Surface Of TS-1 Research Articles

Enhanced catalytic performance for gas phase epoxidation of propylene with H2 and O2 by multiple pretreated Au/TS-1 catalysts

Direct epoxidation of propylene (C3H6) with hydrogen (H2) and oxygen (O2) over Au/TS-1 catalyst was promising way for the synthesis of propylene oxide (PO). However, high selectivity of PO (>95 %) and conversion of C3H6 (>5 %) cannot be achieved at the same time. The industrialization process was severely restricted. In this paper, Au/TS-1 catalysts were synthesized by deposition precipitation method with alkali metal promoter. And alkaline gases and silane coupling post-treatment were performed to promote the catalytic activity. The prepared samples exhibited a much better C3H6 conversion (6.5 %) and PO selectivity (95.1 %) compared with general catalyst using normal synthetic technology. Cs2CO3 was beneficial to increasing Au nanoparticles uptake efficiency. Both NH3 and triethoxyvinylsilane post-treatment were good for smaller and more uniform loading of Au nanoparticles. The decreasing in surface hydroxyl density effectively alleviated the occurrence of PO ring opening isomerization. The increased hydrophobicity of TS-1 surface was conducive to the rapid desorption of generated PO and significantly increased PO selectivity. Multiple pretreatment was also favorable for extending the lifetime of Au/TS-1 catalyst.

Synthesis of titanium silicalite-1 supported zinc catalysts for efficient and clean epoxidation of 1-hexene and methyl oleate

To improve the catalytic epoxidation activity of conventional TS-1 zeolite under acid-free conditions, a series of TS-1-supported zinc (xZn/TS-1) catalysts were prepared and evaluated in the epoxidation of 1-hexene and methyl oleate (MO) with H2O2 oxidant. The microstructure of xZn/TS-1 was investigated using various characterization techniques, and the results showed that the introduction of Zn species was not only well dispersed on the surface of TS-1 but also did not disrupt the crystal structure of TS-1 and tetrahedral framework titanium. Furthermore, the Ti-O-Zn structure can be formed between Zn and Ti species through O-atomic coordination, which improves the vulnerability of the Ti-O bond to attack the H2O2 molecule, and ultimately facilitates the epoxidation reaction between 1-hexene and MO. In addition, the 2% Zn/TS-1 catalysts showed optimal conversions of 45.7 % and 75.41 % for 1-hexene and MO, respectively, and exhibited good catalytic stability and regeneration during the epoxidation process.

Atomically dispersed nano Au clusters stabilized by Zr on the TS-1 surface: Significant enhancement of catalytic oxidation ability using H2 and O2

Au and Zr are uniformly loaded on the surface of TS-1 by coprecipitation method to obtain atomically dispersed Au-Zr binary clusters. The interaction between Au clusters, Zr and TS-1 is analyzed by Independent Gradient Model based on Hirshfeld partition (IGMH), adsorption energy of Au cluster, Mayer bond order. It is found that the existence of Zr is conducive to the stability of nano Au on TS-1 surface. The catalyst is applied to the gas phase epoxidation of C3H6 to obtain 14.06 % initial conversion, 93.93 % initial selectivity and 479.52 gPO·kgcat-1·h-1 initial productivity. It shows good stability in the continuous test for more than 50 h. Density functional theory (DFT) is used to calculate the possible catalytic reaction mechanism on the surface of atomically dispersed Au clusters. The whole process from C3H6 epoxidation reaction to catalyst regeneration is completely described. In the analysis of H2O desorption, the concept of “relay desorption” is proposed. Combined with charge and surface electrostatic potential analysis, the different attack directions of C3H6 on the catalyst surface are discussed in detail. This will provide guidance and help for the synthesis and catalytic application of nano Au catalysts.

Epoxidation of light olefin mixtures with hydrogen peroxide on TS-1 in a laboratory-scale trickle bed reactor: Transient experimental study and mathematical modelling

Direct epoxidation of light olefin mixtures with hydrogen peroxide and titanium silicalite (TS-1) catalyst is interesting from a pure scientific viewpoint and it might have a considerable economic and environmental advantages. Direct epoxidation of olefin mixtures implies a significant process intensification as the separation steps of alkenes prior to the epoxidation process is avoided. Binary and ternary mixtures of ethene, propene and 1-butene were selectively epoxidized with hydrogen peroxide in the presence of TS-1 as the heterogeneous catalyst. Methanol was used as the solvent. Transient and stationary kinetic experiments were conducted in a laboratory-scale trickle bed reactor, which was operated under atmospheric pressure and isothermal conditions at 15–55 °C. The experiments were designed to investigate the kinetics of the epoxidation of light olefins at different temperatures, alkene-to-hydrogen peroxide molar ratios as well as gas and liquid residence times in the trickle bed reactor. The recorded transient responses of the reaction products confirmed that the components in the alkene mixtures are epoxidized simultaneously. The epoxide selectivity was 90 % or higher in most experiments; ring-opening products formed from the epoxides and methanol were observed as by-products. The concentration maxima of epoxides during the transient experiments were explained by accumulation of the epoxide products inside the catalyst, which resulted in partial blocking of active sites. After-treatment of the catalyst with methanol and nitrogen completely restored the initial activity. Kinetic modeling was applied, based on presumed elementary steps on the TS-1 surface to describe the behavior of the system at steady state conditions. The trickle bed reactor was described with a dynamic multiphase model, taking into account the kinetic and mass transfer effects. The numerical values of the activation energies, kinetic constants and mass transfer parameters were estimated by nonlinear regression analysis. The model gave a satisfactory description of the experimental data.

Hydrophobically modified Pd membrane for the efficient purification of hydrogen in light alcohols steam reforming process

The ability to selectively remove H2 from the product has made palladium (Pd) membrane reactor a good choice for steam reforming reaction. However, carbonaceous deposited on the surface of Pd membrane during reaction hindered its industrial application. In order to protect Pd membrane from being poisoned by water and light alcohols, a TS-1/Pd composite membrane was prepared by a facile one-step hydrothermal method combined with silane coupling treatment. The zeolite layer acted as a protective armor by keeping poisonous species away from the Pd bulk, and the silanization process increased the hydrophobicity by reducing the hydroxyl density on the surface of TS-1/Pd composite membrane. After 100 h’s exposure in the steam reforming condition, the percentage of carbon content was only 0.95% for the TS-1/Pd membrane, compared with 13.20% for the pure Pd membrane. The H2 permeability and H2/N2 selectivity of the TS-1/Pd remained constant, while that for pure Pd membrane fell by 50% and 80%, respectively. The significantly improved resistance to carbon deposition provides possibility for the large-scale application of Pd membrane reactor in hydrogen production via steam reforming.

Engineering three-layer core–shell S-1/TS-1@dendritic-SiO2 supported Au catalysts towards improved performance for propene epoxidation with H2 and O2

The advocacy of green chemical industry has led to the development of highly efficient catalysts for direct gas-phase propene epoxidation with green, sustainable and simple essence. The S-1/TS-1@dendritic-SiO2 material with three-layer core–shell structure was developed and used as the support for Au catalysts, which showed simultaneously fantastic PO formation rate, PO selectivity and stability (over 100 h) for propene epoxidation with H2 and O2. It is found that silicalite-1 (S-1) core and the middle thin layer of TS-1 offer great mass transfer ability, which could be responsible for the excellent stability. The designed dendritic SiO2 shell covers part of the acid sites on the external surface of TS-1, inhibiting the side reactions and improving the PO selectivity. Furthermore, three kinds of SiO2 shell morphologies (i.e., dendritic, net, mesoporous shell) were designed, and relationship between shell morphology and catalytic performance was elucidated. The results in this paper harbour tremendous guiding significance for the design of highly efficient epoxidation catalysts.

Mononuclear gold species anchored on TS-1 framework as catalyst precursor for selective epoxidation of propylene

Deposition of gold on supports can produce catalytically active forms of gold as well as spectators, but previous understanding of the nature of active immobilized precursors is poor. By using synchrotron X-ray powder diffraction (SXRD) and X-ray absorption spectroscopy (XAS) techniques, we report a novel synthesis and structural elucidation of atomically dispersed gold species anchored to the internal surface of TS-1 as K+Au(OH)2Na+(Of)3 (“f” signifies the framework atoms of TS-1 in the formula.). It is found that the choice of alkali ions plays a crucial role in nucleation and stabilization of the atomic precursor. These anchored single Au upon controlled reduction in H2 can form uniform gold clusters in direct contact with the TS-1 surface containing isolated Ti sites: their interface exhibits excellent specificity and stability towards epoxidation of propylene in H2/O2 due to synergetic effect.

Manganese-containing hollow TS-1: Description of the catalytic sites and surface properties for solvent-free oxidation of ethylbenzene

Hollow MnOx/TS-1 catalyst was prepared by dissolution-recrystallization and impregnation method, and its catalytic activity was evaluated in aerobic oxidation of ethylbenzene under solvent-free conditions. Tetrahedral Ti4+ and MnOx species homogeneous dispersed on the hollow TS-1 surface and strong favourable synergic interactions between them occurred, which supported by the comprehensive analysis of XRD, N2 physical adsorption, TEM, FTIR, UV–vis, XPS and Raman spectroscopy. The virtue of such synergic effect was reflected in a catalytic efficiency enhancement of valuable ketone and alcohol products (TOF=137h−1): MnOx/TS-1 catalyst showed about 2.2 times higher activity compared to MnOx/Silicalite-1 references. Furthermore, the Mn species content and calcination temperature of the MnOx/TS-1 catalyst presented significant effects of lower-nuclearity Mn species on the structural, chemical, and catalytic properties. Based on the theoretical calculations, the reaction mechanism was proposed where the cleavage of the longer methylene CH bond (1.0935Å) of ethylbenzene and OO bond (1.5267Å) of alkyl hydroperoxide over the OTiOMn sites is a key step to yield radical continuously for recycle.

Effective hierarchization of TS-1 and its catalytic performance in cyclohexene epoxidation

The presented data showed that the chemical treatment of TS-1 with alkaline medium resulted in the formation of highly developed hierarchical structures. The esterification of the hydroxyl groups by methanol allowed modifying the hydrophobicity of TS-1 surface and obtaining truly micro/mesoporous material. The preservation of microporous characteristics was confirmed by XRD and low temperature nitrogen sorption studies. Detailed information on acidic properties of mesoporous titanosilicalites was delivered by IR studies of pyridine sorption and implicitly from 29Si MAS NMR investigations. Well-developed internal mesoporosity together with the retaining of Ti4+ atoms in tetrahedral framework positions offered 7-fold higher catalytic activity for the conversion of cyclohexene molecules than the native microporous TS-1. The selectivity to epoxide reached the value of 96% for the most efficient mesoporous titanosilicate.

A promising ozone-based advanced oxidation process for effective generation of hydroxyl radicals in acidic solution

The oxidative efficiency of H2O2/O3 in the presence or absence of titanium silicalite of TS-1 was investigated at pH value of 3.0, in which acetic acid was selected as the target organic compound owing to its inert to ozone. The removal rate of acetic acid by H2O2/O3 was negligible (5.6% in 30min) because of the impossible deprotonation reaction of H2O2 in acidic solution. However, addition of titanium silicalite of TS-1 could greatly improve the oxidative efficiency of H2O2/O3 (29% in 30min). The results of effects of different parameters such as concentration of H2O2, concentration of TS-1, rate of ozone input, and pH value, on the oxidative efficiency of TS-1/H2O2/O3 showed that the degradation of HAc by TS-1/H2O2/O3 was controlled by the transfers of reactants (including ozone and HAc) to the surface of TS-1. The tests of addition of tert-butyl alcohol and dimethyl sulfoxide (DMSO) both confirmed generation of hydroxyl radicals in this process. The rate of generation of hydroxyl radicals could be controlled by adjusting the concentration of H2O2. The mechanism for generation of hydroxyl radicals might be the reaction of some reactive oxygen species (including Ti(IV)-superoxide and Ti(IV)-hydroperoxide/peroxide), which resulted from the interaction of TS-1 with H2O2, with dissolved ozone. The results are of significance for the effective pretreatment of acidic wastewater containing refractory ozone-inert organic matter.

Insights into size-dependent activity and active sites of Au nanoparticles supported on TS-1 for propene epoxidation with H2 and O2

Propene epoxidation with H2/O2 is a typical structure-sensitive reaction. For a given support containing tetra-coordinated Ti species such as TS-1, the catalytic activity is greatly influenced by supported Au nanoparticle size. The identification of size-dependent activity of Au catalyst was achieved over a series of Au nanoparticles (2.6–5.1nm) deposited on the exterior surface of TS-1 by employing uncalcined TS-1. Through this approach, we could obtain very stable Au catalysts with distinguishable and uniform-sized Au particles, which are critical for structure-sensitivity analysis. The PO formation rate (molPO s−1molAu−1) over these catalysts was found to vary with average Au diameter (d) as d−2.7±0.3. Moreover, typical Au nanoparticles on uncalcined TS-1 appeared as truncated cuboctahedron with top facet of (111). Model calculations derived from the representative Au particle shape and the above size-dependent activity were then performed to show that corner sites of Au nanoparticles are dominant Au active sites for propene epoxidation.

Direct propylene epoxidation with H2 and O2 over In modified Au/TS-1 catalysts

Abstract A series of In promoted Au/TS-1 catalysts was prepared and tested for direct propylene epoxidation with H 2 and O 2 . The In promotion could effectively enhance the reactivity and stability of the catalysts. A PO formation rate of 56 g PO h − 1 kg cat − 1 was obtained over a 0.57Au/0.4In-TS-1 catalyst, which was about 80% enhancement compared to an un-promoted 0.25Au/TS-1 catalyst (32 g PO h − 1 kg cat − 1 ). The enhancement was due to a higher Au capture efficiency by the modification of In on the TS-1 surface, and a higher dispersion of Au species in the catalyst.

Structural Characterization of Tungsten Oxides Supported on Titanium Silicalite

Titanium silicalite (TS-1) is known as an active material catalyst in the epoxidation reaction. In t his study, tungsten oxides (WO 3) with various loading amount have been supported on the TS-1 to increase of the cataly tic acti- vity of the TS-1 material. The solids structure and property were investigated by X-ray diffraction (XRD), temperature programmed reduction (TPR), ultra violet-visible dif fuse reflectance (UV-Vis-DR) and infrared (IR) spectroscopy and scanning electron microscopy (SEM) techniques. The results showed that the structure of TS-1 is not col lapsed after impregnation of WO 3. It was also found that tungsten species have interacted with the silanol groups on the surface of TS-1.

Characterization and Catalytic Performance of Niobic Acid Dispersed over Titanium Silicalite

Niobic acid,Nb2O5⋅nH2O, has been supported on the titanium silicalite by impregnation method. The obtained materials were characterized by X-ray diffraction, infrared, and ultra-violet—visible diffuse reflectance spectroscopy, temperature programmed reduction, pyridine adsorption, and field emission scanning electron microscopy techniques. It was demonstrated that the tetrahedral titanium species still retained after impregnation of niobic acid. The results revealed that niobium species interacted with hydroxyl groups on the surface of TS-1. The niobium species in the catalysts are predominantly polymerized niobium oxides species or bulk niobium oxide with the octahedral structure. All catalysts showed both Brønsted and Lewis acid sites. The catalysts have been tested for epoxidation of 1-octene with aqueous hydrogen peroxide. It was found that the presence of niobic acid in the catalysts enhanced the rate of the formation of epoxide at the initial reaction time. Diol as a side product was also observed due to the acidic properties of the catalysts.

A Quantum Chemical Study of Comparison of Various Propylene Epoxidation Mechanisms Using H2O2 and TS-1 Catalyst

We present a comparison of the following prominent propylene epoxidation mechanisms using H2O2/TS-1 at a consistent density functional theory (DFT) method: (1) the Sinclair and Catlow mechanism on tripodal site through Ti-OOH species, (2) the Vayssilov and van Santen mechanism on tetrapodal site without Ti-OOH formation, (3) the Munakata et al. mechanism involving peroxy (Ti-O-O-Si) species, (4) the defect site mechanism with a partial silanol nest, and (5) the defect site mechanism with a full silanol nest. We have reproduced the previously published (ethylene epoxidation) pathways (1-3) for propylene epoxidation using larger and SiH3-terminated cluster models of the T-6 crystallographic site of TS-1. Mechanism 5 is a new mechanism reported here for the first time. The use of a consistent level of theory for all the pathways allows for the first time a meaningful comparison of the energetics representing the aforementioned pathways. We have rigorously identified the important reaction intermediates and transition states and carried out a detailed thermochemical analysis at 298.15 K and 1 atm. On the basis of the Gibbs free energy of activation, the Sinclair and Catlow mechanism (Delta G(act) = 7.9 kcal/mol) is the energetically most favorable mechanism, which is, however, likely to operate on the external surface of TS-1 due to the tripodal nature of the Ti site in their model. The newly reported defect site mechanism (with a full silanol nest) is a competitive propylene epoxidation mechanism. There are two main steps: (1) hydroperoxy formation (Delta G(act) = 8.9 kcal/mol) and (2) propylene epoxidation (Delta G(act) = 4.6 kcal/mol). This mechanism is likely to represent the chemistry occurring inside the TS-1 pores in the liquid-phase epoxidation (H2O2/TS-1) process and could operate in direct gas-phase epoxidation (H2/O2/Au/TS-1) as well. If only the propylene epoxidation step is considered, then the Munakata peroxo intermediate (Si-O-O-Ti) is the most reactive intermediate, which can epoxidize propylene with a negligible activation barrier. However, formation of the Munakata intermediate is a very activated step (Delta G(act) = 19.8 kcal/mol). We also explain the trends in the activation barriers in different mechanisms using geometric and electronic features such as orientation of adsorbed H2O2 and propylene, hydrogen bonding, O1-Ti bond distance in the Ti-O1-O2-H intermediate, and O1-O2 stretching in the transition state. Implications of different Ti site models are also discussed in light of the nature of external/internal and nondefect/defect sites of TS-1.

TS-1 loaded with sulfated zirconia as bifunctional oxidative and acidic catalyst for transformation of 1-octene to 1,2-octanediol

Titanium silicalite (TS-1) loaded with sulfated zirconia as bifunctional oxidative and acidic catalyst has been synthesized at various loadings of zirconium (2–20 wt%). Structure and properties of the samples were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), Fourier transform infrared (FTIR) and UV–vis diffuse reflectance (UV–vis DR) spectroscopy techniques. The monolayer dispersion capacity of zirconium on the TS-1 was found to be 0.65 Zr 4+ nm −2 TS-1. The UV–vis DR spectroscopy showed that the tetrahedral coordination of the titanium was observed in all samples, while octahedral zirconium was only observed in the samples containing high amount of zirconium loading (10, 15 and 20 wt%). The TPR profiles suggested that the zirconium structure impregnated on the surface of TS-1 with high amount of zirconium loading (15 and 20 wt%) have a similar structure to sulfated zirconia calcined at 500 °C. Adsorption of pyridine onto the samples indicated that Brönsted acid sites are only present in samples with high sulfated zirconia loading, i.e. 15 and 20 wt%. As analyzed by XRD, the formation of Brönsted acid sites is due to the presence of disulfate species on the surface of TS-1. It has been demonstrated that samples with 15 and 20 wt% loadings of sulfated zirconia showed activity towards consecutive transformation of 1-octene to 1,2-octanediol through the formation of 1,2-epoxyoctane using aqueous hydrogen peroxide.

Characterization and reactivity of stannum modified titanium silicalite TS-1 catalysts for transesterification of dimethyl oxalate with phenol

The transesterification of dimethyl oxalate (DMO) with phenol over stannum modified TS-1 was conducted to prepare methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO), which could be used to produce diphenyl carbonate (DPC). The component, structure and phase of TS-1 catalysts with various Sn loadings were investigated. The relationship between the catalytic properties and the Sn loadings was discussed. The results indicated that, although the Sn-modified TS-1 catalysts had fewer Lewis acid sites than the unmodified TS-1, its catalytic activity was increased greatly by the interaction of Sn with Ti–O–SiO 3 weak Lewis acid centers. The catalyst of TS-1 with 2 wt% Sn loadings performed best, giving 50.3% conversion of dimethyl oxalate and 99.2% selectivity to the target products. By means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX), the relationship between the catalytic properties and the structure of Sn dispersed on the surface of TS-1 was studied in detail. At Sn loadings below 2 wt%, Sn was highly dispersed, but at higher loadings it was crystallized into bulk tin dioxide, where the interaction between Ti and Sn was not evidently observed, leading to decreased catalytic activity. XPS results showed that Ti could not be detected even at 1 wt% Sn loadings. EDX results indicated that the content of Ti on the surface decreased with increasing Sn loadings, but the decrease in Ti content was much less than the increase in Sn content. Moreover, NH 3-TPD and FTIR analyses of adsorbed pyridine showed that there were only weak Lewis acid centers on all catalysts and the Sn loadings hardly affected the acid strength of the catalysts.

Preparation and characterization of bifunctional oxidative and acidic catalysts Nb2O5/TS-1 for synthesis of diols

Bifunctional oxidative and acidic catalyst was prepared by incorporation of titanium ion (Ti4+) and niobic acid in zeolite molecular-sieve. The catalysts being active both in oxidation reactions due to the presence of tetrahedral Ti4+, and acid-catalyzed reactions due to the presence of niobic acid. Nb/TS-1 was prepared by hydrothermal synthesis of TS-1, calcination in air and subsequent impregnation of niobium into TS-1. The sample was characterized by XRD, FTIR, UV–vis DR, TPR and pyridine adsorption techniques. The XRD analysis of Nb/TS-1 revealed that the MFI structure of the TS-1 support was found to be intact upon incorporation of niobium. The infrared spectra showed that the tetrahedral titanium in the TS-1 is still remained after impregnation with niobium while based on the UV–vis DR result, the niobium species are in the octahedral structure. On the basis TPR and infrared of hydroxyl groups results, it is concluded that niobium species interacted with the silanols on the surface of TS-1. Pyridine adsorption study shows both Brønsted and Lewis acid sites are present in Nb/TS-1. The catalytic results in the transformation of 1-octene to 1,2-octanediol through the formation of 1,2-epoxyoctane by using Nb/TS-1 indicate that the production of epoxide and diol was correlated with the presence of oxidative and Brønsted acidic sites in the catalyst.

Structural analysis ofTityus serrulatusTs1 neurotoxin at atomic resolution: insights into interactions with Na+channels

The structure of the Ts1 toxin from the Brazilian scorpion Tityus serrulatus was investigated at atomic resolution using X-ray crystallography. Several positively charged niches exist on the Ts1 molecular surface, two of which were found to coordinate phosphate ions present in the crystallization solution. One phosphate ion is bound to the conserved basic Lys1 residue at the Ts1 N-terminus and to residue Asn49. The second ion was found to be caged by residues Lys12, Trp54 and Arg56. Lys12 and Tyr/Trp54 residues are strictly conserved in all classical scorpion beta-neurotoxins. The cavity formed by these residues may represent a special scaffold required for interaction between beta-neurotoxins and sodium channels. The charge distribution on the Ts1 surface and the results of earlier chemical modification studies and side-directed mutagenesis experiments strongly indicate that the phosphate-ion positions mark plausible binding sites to the Na(+) channel. The existence of two distinct binding sites on the Ts1 molecular surface provides an explanation for the competition between Ts1, depressant (LqhIT2) and excitatory (AaHIT) neurotoxins.

Influence of Pore and Crystal Size of Crystalline Titanosilicates on Phenol Hydroxylation in Different Solvents

The hydroxylation of phenol into catechol and hydroquinone with aqueous H2O2 (30%) and titanium-substituted molecular sieves (TS-1 and Al-free Ti-Beta) was investigated to understand the role of the zeolite structure, the crystal size, the external surface of the zeolite, and the nature of the solvent on the product selectivity. Comparing Al-free Ti-Beta and TS-1 samples with similar pore lengths, the activity as well as the ratio of catechol to hydroquinone was significantly higher for Al-free Ti-Beta, showing diffusional constraints for the conversion of phenol and geometric constraints for the formation of catechol. The diffusional constraints in the conversion of phenol were confirmed by using small crystallites of TS-1. The role of the external surface of TS-1 in the phenol hydroxylation was investigated by inertization of the external surface, using cycles of low-temperature chemical vapor deposition (CVD) of tetraethoxysilane followed by high-temperature calcination. Consecutive CVD cycles led to a slight increase of the selectivity toward hydroquinone for all tested solvents as well as a reduction of the coke formation in methanol and water. The ratio of hydroquinone to catechol, however, did not change much, indicating that catechol must also be formed inside the pore structure. A kinetic analysis of the reaction data with the parent and surface-inertized TS-1 revealed that the role of the external surface in terms of both activity and selectivity is significant and dependent on the solvent used. A reaction mechanism consistent with the observed enhanced selectivity for hydroquinone in protic solvents is proposed.