Rafael van Grieken

Direct syntheses of ordered SBA-15 mesoporous materials containing arenesulfonic acid groups

SBA-15 mesoporous silica has been functionalized with arenesulfonic acid groups by means of a one-step simple synthesis approach involving co-condensation of tetraethoxysilane (TEOS) and 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS) in the presence of a poly(alkylene oxide) block copolymer (Pluronic 123) under acid silica-based catalysis. The resultant materials show hexagonal mesoscopic order and pores sizes up to 60 A, with acid exchange capacities of ca. 1.3 mequiv. H+ per g SiO2 and surface areas up to 600 m2 g−1. The sulfonic groups anchored to the silica surface of the pore walls are thermally stable to temperatures up to 380 °C and resistant to leaching in organic and aqueous solutions under mild conditions. 31P MAS NMR measurements of chemically adsorbed triethylphosphine oxide and the catalytic properties confirm the presence of Bronsted acid centers in these mesoporous materials containing arenesulfonic acid groups that are stronger than those found in propanesulfonic-modified SBA-15 and Al-MCM-41.

Analogies and differences between photocatalytic oxidation of chemicals and photocatalytic inactivation of microorganisms

This study reports the analogies and differences found when comparing TiO(2) photocatalytic treatment for chemical oxidation and microorganisms inactivation, using methylene blue and Escherichia coli as references, respectively. In both processes the activation is based on the same physicochemical phenomena and consequently a good correlation between them is observed when analyzing the effect of operational variables such as catalyst concentration or incident radiation flux, both factors influencing common stages such radiation absorption and generation of reactive oxygen species. However, different microbiological aspects (osmotic stress, repairing mechanism, regrowth, bacterial adhesion to the titania surface, etc) makes disinfection kinetics significantly more complex than the first-order profiles usually observed for the oxidation of chemical pollutants. Moreover, bacterial inactivation reactions are found to be extremely sensitive to the composition of water and modifications of the catalysts in comparison with the decolorization of the dye solutions, showing opposite behaviors to the presence of chlorides, incorporation of silver to the catalysts or the use of different types of immobilized TiO(2) systems. Therefore, the activity observed for the photocatalytic oxidation of organics can not be always extrapolated to photocatalytic disinfection processes.

Emerging micropollutant oxidation during disinfection processes using UV-C, UV-C/H2O2, UV-A/TiO2 and UV-A/TiO2/H2O2.

Regeneration of wastewater treatment plant effluents constitutes a solution to increase the availability of water resources in arid regions. Water reuse legislation imposes an exhaustive control of the microbiological quality of water in the operation of disinfection tertiary treatments. Additionally, recent reports have paid increasing attention to emerging micropollutants with potential biological effects even at trace level concentration. This work focuses on the evaluation of several photochemical technologies as disinfection processes with the aim of simultaneously achieving bacterial inactivation and oxidation of pharmaceuticals as examples of emerging micropollutants typically present in water and widely studied in the literature. UV-C-based processes show a high efficiency to inactivate bacteria. However, the bacterial damages are reversible and only when using H(2)O(2), bacterial reproduction is affected. Moreover, a complete elimination of pharmaceutical compounds was not achieved at the end of the inactivation process. In contrast, UV-A/TiO(2) required a longer irradiation time to inactivate bacteria but pharmaceuticals were completely removed along the process. In addition, its oxidation mechanism, based on hydroxyl radicals (OH), leads to irreversible bacterial damages, not requiring of chemicals to avoid bacterial regrowth. For UV-A/TiO(2)/H(2)O(2) process, the addition of H(2)O(2) improved Escherichia coli inactivation since the cell wall weakening, due to OH attacks, allowed H(2)O(2) to diffuse into the bacteria. However, a total elimination of the pharmaceuticals was not achieved during the inactivation process.

Co/HZSM-5 catalyst for syngas conversion: influence of process variables

The effects of process variables on the activity of a Co/HZSM-5 zeolite bifunctional catalyst for the conversion of syngas to hydrocarbons were studied. The catalyst was prepared by incipient-wetness impregnation from aqueous solutions of cobalt and thorium nitrate, the latter used as promoter. The reactions were carried out in a fixed-bed integral reactor. A simple two-level factorial design was not sufficient to describe the dependence of C6 + yield and C6 + selectivity on the process variables. A composite factorial design led to two response surfaces, describing the dependence of yield and selectivity on temperature (240–320°C), space velocity (0.5–1.3 h−1), COH2 feed ratio (0.5–1.9 molar) and pressure (0.1–4.3 MPa), with a deviation error of ∼20%. The catalyst showed a better selectivity towards higher hydrocarbons than a physical mixture of ZSM-5 zeolite and a conventional Fischer-Tropsch catalyst and only slow deactivation, affecting mainly the C6 + selectivity. This deactivation is probably due to coke deposition on the active surface sites, that is, cobalt particles and acid sites of the zeolite.

Synthesis of titanium silicalite-1 from an SiO2–TiO2 cogel using a wetness impregnation method

An alternative to the conventional methods of TS-1 synthesis is based on the wetness impregnation of an SiO2–TiO2 cogel, which leads to more effective Ti incorporation in a simpler way.

Cobalt/HZSM-5 zeolite catalyst for the conversion of syngas to hydrocarbons

Abstract Physical and chemical properties as well as the activity and selectivity of Co/HZSM-5 zeolite bifunctional catalyst have been studied for conversion of synthesis gas. These catalysts were prepared by incipient wetness impregnation with different conditions of drying, calcination and reduction. The cobalt content in the catalyst and the effect of thoria, as promoter, were also studied. The catalysts prepared were characterized and tested in a fixed bed continuous reactor system. The results show that drying is the most important step in the preparation, having more active catalysts with fast drying conditions, probably due to the formation of smaller cobalt particles. The interaction between the metal and the zeolite surface seems to contribute significantly to the catalyst activity. Maximum activity of the catalyst is obtained with 1.5 wt.-% of thorium, resulting in an increase of C6+ selectivity. This is explained in terms of a shift in chemisorption properties of the catalyst. The basic character of the promoter affects the zeolite acidity, decreasing the aromatic proportion in the liquid hydrocarbon fraction. Finally, the bifunctional catalyst selected in this study is compared with a physical mixture of a commercial Fischer-Tropsch catalyst and HZSM-5 zeolite.

On the Sn(II) and Sn(IV) incorporation into the AFI-structured AlPO4-based framework: the first significantly acidic SnAPO-5

Both Sn(II) and Sn(IV) chlorides were tested as sources for tin incorporation into an AlPO4-5 framework. N-Methyldicyclohexylamine (MCHA) was chosen as a structure-directing agent, taking advantage of its reported high specificity towards AFI-structured AlPO4-based materials. Pure AFI materials were successfully produced, irrespective of the Sn source in a wide range of gel compositions. Whereas the different characterization techniques of the Sn(IV)APO-5 materials certify the unfavourable (or at least low-quality) incorporation of Sn, as expected from previous studies, there is no doubt about the right Sn(II) incorporation into the AlPO4 framework. The amount of Sn(II) able to be properly incorporated into the AlPO4-5 structure is significantly higher than that described in the literature for Sn(IV)APO-5 materials as well as for the Sn(IV)APO-5 materials prepared in this work. For the first time, AlPO4-based microporous catalysts were tested in the Friedel–Crafts acylation of anisole. Supporting the characterization results, Sn(IV)APO-5 and especially Sn(II)APO-5 were active catalysts in such reactions which require acid centers to take place. Since all tested AlPO4-based materials (pure AlPO4-5, SAPO-5 and SnAPO-5) possess an AFI structure and similar surfaces areas, the extent of the acylation of anisole was taken as indirect proof of acidic strength. The conversion given by pure AlPO4-5 was negligible in comparison with Sn(II)APO-5, which overcomes the activity of the SAPO-5 and even that of a standard zeolite H-beta.

Solar photocatalytic disinfection with immobilised TiO2 at pilot-plant scale

The photocatalytic disinfection efficiency has been investigated for two immobilized TiO(2) catalytic systems (wall reactor and fixed-bed reactor) in a solar pilot plant. Their performances have been compared with the use of a slurry reactor and the solar disinfection without catalyst. The use of photocatalytic TiO(2) wall reactors does no show clear benefits over the solar disinfection process in the absence of catalyst. The reason is that the efficiency of the solar disinfection is so high that the presence of titania in the reactor wall reduces the global efficiency due to the competition for the absorption of photons. As expected, the maximum efficiency was shown by the slurry TiO(2) reactor, due to the optimum contact between bacteria and catalyst. However, it is noticeable that the use of the fixed-bed reactor leads to inactivation rate quite close to that of the slurry, requiring comparable accumulated solar energy of about 6 kJ L(-1) to achieve a 6-log decrease in the concentration of viable bacteria and allowing a total disinfection of the water (below the detection limit of 1 CFU mL(-1)). Not only the high titania surface area of this configuration is responsible for the bacteria inactivation but the important contribution of the mechanical stress has to be considered. The main advantage of the fixed-bed TiO(2) catalyst is the outstanding stability, without deactivation effects after ten reaction cycles, being readily applicable for continuous water treatment systems.

Simultaneous photocatalytic oxidation of pharmaceuticals and inactivation of Escherichia coli in wastewater treatment plant effluents with suspended and immobilised TiO(2).

Simultaneous Escherichia coli inactivation and oxidation of pharmaceuticals in simulated wastewater treatment plant effluents has been investigated using a photocatalytic treatment with TiO(2) in suspension and immobilised onto a fixed-bed reactor. Non-photocatalytic reference experiments of dark adsorption and photolysis showed a higher sensitivity of E. coli towards the chemical composition of water in comparison with the concentration of pharmaceuticals that remains unaffected. Moreover, it must be underlined that the presence of pharmaceuticals (including antibiotics) did not seem to affect the bacterial viability at such low concentrations. Concerning photocatalytic experiments, both suspended and immobilised TiO(2) were able to simultaneously inactivate and oxidise both kinds of pollutants (bacteria and pharmaceuticals). The fixed-bed reactor showed similar activity to that of the slurry without deactivation after several cycles of reuse. That makes TiO(2) photocatalysis a quite interesting technology for the treatment of drinking water supplies or wastewater plant effluents, allowing the removal of emerging contaminants such as pharmaceuticals during the disinfection treatment.

Mechanism of CIT-6 and VPI-8 Crystallization from Zincosilicate Gels

The crystallisation of CIT-6, a large-pore zincosilicate with the framework topology of zeolite Beta and synthesised from clear hydrogels that contain, tetraethylammonium (TEA+), Li+ and Zn2+ cations, proceeds initially through the formation of an amorphous solid that incorporates all the initial Zn species. Nucleation of the *BEA phase is effected by reorganisation of the amorphous phase, whereas crystal growth involves the incorporation of soluble species also. A highly crystalline CIT-6 material is obtained after 164 h of synthesis at 140 degrees C. Scanning electron microscopy (SEM) shows that this sample exhibits two different types of crystals: well-defined pseudo-cubic crystals and rounded crystals. The latter has a broad crystal-size distribution. If crystallisation is continued with longer synthesis times, the VPI-8 crystalline phase appears, and a new population of needle-shaped crystals is detected in the SEM images. This new crystalline phase is nucleated on the surface of the rounded CIT-6 crystals, which disappear as the crystallisation progresses, while no changes are observed in the population of pseudo-cubic CIT-6 crystals. At higher crystallisation temperatures these phase transformations are accelerated, and the formation of VPI-8 is favoured over that of CIT-6.