Volume 14, Issue 3 - Special Issue: In Honour of Professor Serge Kaliaguine (Part I), Guest Editors: Benito Serrano Rosales and Ying Zheng

In this paper, we summarize recent research efforts from our laboratory concerning the application of core/shell structured materials for sustainability. Special attention is paid to the synthesis of different core/shell materials from nanoscale to microscale by various methods. The potential applications of our prepared novel materials with core/shell configuration are discussed, which illustrates the diversity of situations where the core/shell structure brings a simple solution to different materials design problems.

This study reports phenol degradation using several TiO 2 photocatalysts (DP25, Anatase 1, Hombikat UV-100, Anatase 2) in a Photo-CREC Water-II Reactor. The physicochemical properties of the photocatalysts used, such as crystallinity, superficial area, and pore size distribution are reported. Reactor efficiencies are calculated using both Quantum Yields (QYs) and Photochemical and Thermodynamic Efficiency Factors (PTEFs). This is accomplished using phenol and phenol intermediate photoconversion rates. This allows the determination of hydroxyl radical consumption rates, at every step of the photodegradation process. With these data, and with the absorbed photon rates, energy efficiencies are calculated. It is shown that for the best performing photo catalysts the maximum QYs reach 50 % levels. These favourable photoconversion efficiencies confirm the critical importance of having available highly performing photocatalysts and photoreactors, such is the case of Photo-CREC Water-II Reactor unit.

Examination of the hydrotreatment of light cycle oil over a dispersed MoS 2 catalyst was conducted in a batch reactor at 375 °C and 1,500 psi. Hydrodesulfurization, hydrodenitrogenation, hydrogenation of aromatics, and hydrocracking activity were all analyzed. Diaromatics are more reactive than monoaromatics. Different sulfur compounds have experimental rates of elimination following the trend of BT>1MBT>> 2MBT>3MBT>4MBT>>DBT≈1MDBT≈2MDBT≈3MDBT. BT and its derivatives are very reactive and easy to eliminate, but become harder to convert as they gain methyl groups. DBTs are harder to eliminate than BTs, and don’t experience significant changes in reactivity as they gain methyl groups. This difference indicates that steric hindrance is more significant in supported catalysts than in unsupported catalysts. Different nitrogen compounds have experimental rates of elimination following the trend of Anilines> Indoles> Carbazoles.

Pure chitosan (CS) and hybrid ionic liquid-chitosan membranes loaded with 5 wt% 1-ethyl-3-methylimidazolium acetate ([emim][Ac]) ionic liquid were prepared in order to improve the thermal behavior of supported ionic liquid membranes (SILMs) for CO 2 separation. Gas permeability, solubility and diffusivity were evaluated in the temperature range 298–323 K. The temperature influence was well described in terms of the Arrhenius–van’t Hoff exponential relationships. Activation energies were calculated and compared with those obtained for SILMs with the same ionic liquid. The introduction of this ionic liquid in the hybrid solid membrane decreases the permeability activation energy, leading to a lower influence of the temperature in the permeability and diffusivity. Moreover, the thermal behavior is similar to pure chitosan membranes, and the mechanical strength and flexibility were improved due to the introduction of the ionic liquid in the polymer matrix.

This study reports on the first assessment of the treatment of sediment contaminated by organotin compounds using homogenous and heterogeneous photocatalysis. Photo-Fenton and photocatalysis of low level (µg/L) organotins in water were carried out. A quasi-complete degradation of tributyltin (TBT) in water (99.8%) was reached after 30 and 7 min for photocatalytic and photo-Fenton treatment, respectively. For the first time decontamination of highly polluted marine sediments by photo-oxidation proves that the use of UV and the production of hydroxyl radicals are an efficient way to treat organotins adsorbed onto marine sediment despite the complexity of the matrix.

A chromium incorporated mesoporous silicate structured Cr/MCM-41 type catalyst was synthesized following a one-pot hydrothermal route and tested in dehydrogenation of isobutane to isobutene in a Pd membrane reactor. Characterization results of the catalyst proved that it had ordered pore structure with a narrow pore size distribution. This catalyst showed quite high activity for the dehydrogenation of isobutane. Membrane reactor tests performed at 823 K proved the advantages of in-situ removal of produced hydrogen from the reaction zone through the membrane, on isobutene yield. In fact, much higher isobutane conversions than the conversion values predicted from the equilibrium calculations were achieved at this temperature. However, at a higher temperature of 873 K, the Pd membrane itself also showed catalytic activity for the decomposition of isobutane and isobutene. As a result, lower isobutene selectivity values and quite high methane and propene selectivities were observed at this temperature. Cracking reactions also caused coke formation at 873 K, especially at high pressure differences across the membrane (70 kPa). Increase of pressure difference across the membrane caused fast removal of hydrogen from the reaction zone, which facilitated coke formation due to cracking reactions.

This study provides theoretical support to a recent promising ZSM5 catalyst used for the selective desulfurization of light diesel type compounds (Al-Bogami and de Lasa 2013; Al-Bogami, Moreira, and de Lasa 2013). With this end, Molecular Dynamics (MD) simulations employing a rigid silicalite structure are developed to calculate self-diffusivities of n-Dodecane (n-C12) and Benzothiophene (BZT) in a silicalite structure. The simulations are performed at 573 K, 623 K, 673 K and 723 K at a fixed loading of 1 molecule per unit cell to study the temperature effect on diffusivity coefficient. In addition, a number of simulations which are developed to investigate four molecule loadings (corresponding to 0.25, 0.5, 0.75 and 1 molecule per zeolite unit cell) at 723 K. MD simulations, show a self diffusivity of BZT one order of magnitude higher than that of n-C12 self diffusivity at all temperatures investigated. This is the case in spite of BZT having a critical molecular diameter of 6 Å when compared to the 4.9 Å diameter of n-C12. In addition, the self diffusivity coefficient is found to increase with temperature for both n-C12 and BZT. Furthermore, the results obtained show that the self diffusivity of n-C12 decreases as the number of n-C12 molecules per zeolite unit cell increases. On the other hand, it is observed that the self-diffusivity coefficient for BZT remains fairly constant and drops at a loading of 1 molecule per zeolite unit cell only. These coefficients show that differences in n-C12 and benzothiophene diffusivities favours desulfurization with selective benzothiophene adsorption and sulfur species removal as coke (Al-Bogami and de Lasa 2013).

The present work is aimed at unsteady-state mathematical modeling and simulation of the steam gasification of a single char particle. The unsteady state diffusion-reaction competitive gasification of a porous non-catalytic solid (char) was solved numerically using the staggered grid finite volume method (SGFVM). It was assumed that the char particle is spherical in shape and there is no change in its size during the gasification, and temperature variation within the particle is negligible. The model is capable of predicting detailed point-to-point reaction, diffusion, and concentration profile in a spatiotemporal domain inside the particle. The study revealed that the gasification of the char particle at higher temperature (>1,100 K) bear a resemblance to the shrinking core model and at a lower temperature (<1,100 K) it follows the progressive conversion model. The study also includes the effects of the temperature, time, and carbon concentration on the rate and conversion inside the char particle.

A famous hard-template method (HT), coprecipitation method (PC), and complex method (CA) were used to prepare CeCu composite oxide catalysts. The prepared catalysts were characterized via XRD, BET, Raman, XPS, FI–IR, and O 2 –TPD, and their catalytic activity and stability were evaluated for the propyl acetate catalytic combustion. The results showed that the CeCu oxide solid solution and oxygen vacancies were formed in the prepared CeCu oxide catalysts, even for CeCu–PC and CeCu–CA having a specific amount of isolated crystalline or amorphous CuO species. Comparing with the CeCu–PC and CeCu–CA of low porosity, CeCu–HT developed a mesoporous structure with a much larger specific surface area through a negative replica on the structure of KIT-6, and in it, CuO was completely dissolved in the CeO 2 lattice to form more CeCu oxide solid solution and a large amount of oxygen vacancies. As a result, the CeCu–HT catalyst has more surface-adsorbed oxygen species, more –OH group which can also change into surface-adsorbed oxygen species at relatively high temperatures, higher oxygen desorption ability, and higher oxygen mobility than CeCu–PC and CeCu–CA. The CeCu–HT catalyst shows high and stable propyl acetate catalytic combustion performance at 190 °C. The propyl acetate catalytic combustion activity on the prepared CeCu oxide catalysts can be ranked as: CeCu–HT > CeCu–PC > CeCu–CA, which follows the orders of CeCu oxide solid solution content, surface-active oxygen content, and oxygen desorption and mobility of the CeCu composite oxide catalysts.

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) is investigated over a commercial NiMoP/γ-Al 2 O 3 catalyst in a micro trickled bed reactor (Micro-TBR) at operating conditions of a reactive distillation (RD) column. An analysis with and without reaction is carried out to have a first understanding on the complex interaction between kinetics and transport phenomena. A set of well-accepted criteria is evaluated to elucidate the presence of heat and mass transport limitations. Residence time distribution (RTD) experiments are performed to evaluate axial dispersion through the estimation of axial dispersion coefficient (D axial,L ) from a convection-dispersion model. Experiments with reaction are carried out using hydrogen and DBT as feedstock at reaction temperatures from 533 to 599 K, pressures from 1.5 to 2.5 MPa and inlet molar flow of DBT from 4 to 12×10 –8 mol.s –1 . A pseudo heterogeneous model accounting for mass transport limitations is used to describe experiments under reaction conditions. The main findings can be summarized as follows: most of RD operating conditions lead to the presence of interfacial mass transport limitations at both interfaces L-S and G-L; convection-dispersion model is able to describe satisfactorily RTD observations, suggesting that axial dispersion phenomena are negligible; conversion of DBT ranges from ca. 22 to 90% having a selectivity to by-product molecules from 30 to 80%, respectively; and the pseudo heterogeneous reaction model describes observations adequately obtaining activation energies ranging from 49 to 62 kJ mol –1 at pressures from 1.5 to 2.5 MPa, respectively. Estimated activation energies are comparatively lower than the activation energies reported in literature for the conventional HDS process, i.e. 40–160 kJ.mol –1 , thereby suggesting an apparent catalytic energy savings by using RD technology.

Surface modification of Zinc oxide nanoparticles (ZnO) with γ-aminopropyltriethoxy silane (APTES) was investigated. Successful surface modification of the nanoparticles was confirmed experimentally by X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The effect of the surface modifier concentration on the grafting density and surface area was studied by CHN elemental analysis and Brunauer–Emmett–Teller (BET) analysis. The photocatalytic activity and UV shielding ability of the surface-modified particles prepared in water-ethanol solvent in the presence of the surface modifiers were compared to those of non-modified particles. As a case study, It was observed by methylene blue (MB) dye degradation experiment that the photocatalytic activity in the presence of modified nanoparticles was lower than that observed with non-modified ZnO nanoparticles. Dispersion stability tests visually showed that APTES grafted nanoparticles had acquired better stability than non-modified ZnO nanoparticles in aqueous solution.

Super acidic nanostructured sulfated aluminum-zirconium binary oxides in mole ratios of Zr 4+ : Al 3+ as 2:1 (SAZ-1), 1:1 (SAZ-2), 1:2(SAZ-3) and the reference catalyst super acidic sulfated zirconia (SZ) were synthesized by a precipitation method. Firstly, the catalytic performance of these four catalysts was evaluated during the isomerization of n-hexane to 2-methyl pentane and 3-methyl pentane, n-heptane and n-octane to their corresponding branched chain isomers at low temperature and pressure conditions (40°C and 1 atm). SAZ-1 performed the highest active and selective isomerization of n-hexane, n-heptane, and n-octane into their corresponding branched chain isomers. The catalytic activity of the reference catalyst SZ was the lowest among the four synthesized catalysts. TEM analysis applied to SAZ-1 and SZ indicated the presence of particle-bulks having average size of 20 nm; moreover, these materials presented an amorphous nature, having no particular surface morphology. XRD confirmed the amorphous structure of SAZ-1 and SZ as well as indicated their internal phase structure. FTIR generated ideas about different linkages and bond connectivities between atoms and groups in SAZ-1 and SZ. Ammonia-TPD of these two materials confirmed the higher super acidic nature of SAZ-1 and lower super acidic nature of SZ. Catalyst evaluation and characterization allowed to propose a reaction mechanism, elucidating a possible role of Brønsted and Lewis acid sites on the studied reaction-catalyst, being the former active sites the main factor leading to isomerization reaction. AFM and SEM pictures indicated the nature of the surface of the catalysts. Nevertheless, SEM analysis before and after the reaction displayed that catalyst morphology was modified and could influence the activity of the catalyst. The use of SAZ-1 is cost saving as well as energy saving.

High purity metoprolol prepared by neutralization of an aqueous solution of metoprolol tartrate is efficiently mineralized to CO 2 and water by photocatalysis with TiO 2 , UV light and a constant flow rate of oxygen. Since the tartrate anions were eliminated, all the HO• generated by photocatalysis reacted efficiently with the aromatic part of the medication. The reaction pathway includes two routes of degradation. The first one includes the transformation of metoprolol to hydroquinone via formation of 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde. Metoprolol is also degraded directly to hydroquinone. Then, this aromatic compound is oxidized to 1,2,4-benzenetriol, which is rapidly oxidized to low molecular weight organic acids before being completely mineralized to CO 2 and water. Kinetic studies indicated that the initial reaction rate of the degradation of metoprolol, 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde is described by the LH-HW model.