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Titanium silicates of MWW structures with different Si/Ti ratios were prepared via hydrothermal synthesis using piperidine as the structure directing agent and boric acid as the crystallization agent. All the syntheses resulted in highly crystalline materials independent of the Si/Ti ratio. The observed morphology showed MWW-like well-defined thin hexagonal platelets. The synthesized Ti-MWW materials exhibited higher surface areas and partial meso-porosity compared to the commercial TS-1 catalyst. The coordination of the Ti-species was investigated by UV–vis- and IR-spectroscopy. The MWW titanium silicates were tested for the catalytic performance in the epoxidation of propylene in a laboratory-scale trickle bed reactor to compare their clear different physico-chemical properties with the commercial TS-1. The synthesized Ti-MWW materials showed significantly higher catalytic activities, up to 3.5 times, using acetonitrile as the solvent and enhanced epoxide selectivities partially up to 100% in methanol unlike TS-1. The effect of the Ti content in the MWW and the calcination conditions were investigated in propylene epoxidation, revealing the beneficial effect of a lower calcination temperature and an increased Ti content on the activity. The catalytic results were correlated with the physico-chemical properties of the synthesized materials. Graphical Abstract

Methyl levulinate was selectively formed from glucose and methanol over a copper modified Beta zeolite bifunctional catalyst at 180 °C under argon atmosphere. The selectivity to methyl levulinate substantially exceeded previously reported in the open literature results. The copper modification was done through an ion-exchange method using a solution of copper nitrate, followed by drying and calcination of the catalyst. Copper modification changed the distribution of acid sites namely, less Brønsted and more Lewis sites were observed with FTIR using pyridine adsorption. Application of the proton form H-Beta-25 gave the methyl levulinate yield of ca. 89%, which could be elevated with the addition of copper, as the apparent selectivity exceeds 99%, assuming that methyl glucosides are eventually transformed to methyl levulinate. The non-acidic Cu/SiO2 catalyst was completely inactive in methyl levulinate formation. Metal modification of Beta zeolite with Sn and Zn did not perform as well as Cu in the formation of methyl levulinate during glucose transformation.

Formic acid is one of the key components in green chemistry being involved in energy storage, production of chemical intermediates and fuel components. Therefore the knowledge of its stability is of crucial importance and a systematic study of its decomposition is needed. The kinetics of formic acid decomposition to hydrogen and carbon dioxide was investigated in a laboratory-scale fixed bed reactor at 150–225 °C and atmospheric pressure. Palladium nanoparticles deposited on porous active carbon Sibunit were used as the heterogeneous catalyst. The catalyst was characterized by nitrogen physisorption and high-resolution transmission electron microscopy. The average palladium nanoparticle size was 5–6 nm. The impacts of mass transfer resistance and formic acid dimerization were negligible under the reaction conditions. Prolonged experiments revealed that the catalyst had a good stability. Hydrogen and carbon dioxide were the absolutely dominant reaction products, whereas the amounts of carbon monoxide and water were negligible. The experimental data were described with three kinetic models: first order kinetics, two-step adsorption-reaction model and multistep adsorption-decomposition model of formic acid. The multistep model gave the best description of the data.

Sugar alcohols are obtained by hydrogenation of sugars in the presence of ruthenium catalysts. The research effort was focused on the development of solid foam catalysts based on ruthenium nanoparticles supported on active carbon. This catalyst was used in kinetic experiments on the hydrogenation of l-arabinose and d-galactose at three temperatures (90, 100, and 120 °C) and two hydrogen pressures (20 and 40 bar). Kinetic experiments were carried out with binary sugar mixtures at different d-galactose-to-l-arabinose molar ratios to study the interactions of these sugars in the presence of the prepared solid foam catalyst. The solid foam catalyst preparation comprised the following steps: cutting of the open-cell foam aluminum pieces, anodic oxidation pretreatment, carbon coating, acid pretreatment, ruthenium incorporation, and

This work describes an effective method for the preparation of open-cell ceramic foams for their further use as catalyst supports. The polyurethane sponge replica technique was applied using a ceramic suspension based on a mixture of α-alumina, magnesia and titania and polyvinyl alcohol solution as a liquid component. The polyurethane sponge was etched with NaOH and covered with colloidal silica to obtain better adhesion of the slurry to the walls of the polymeric material onto it. The surface area of the ceramic carrier was increased by adding a layer of γ-alumina. Deposition of an active catalytic phase (Pt) was done by impregnation. Properties of the carriers and the final catalyst were investigated by a number of physico-chemical methods such as TEM, SEM, XRD and computer tomography. Hydrogenation of ethyl benzoylformate was performed to elucidate the catalytic properties of foam catalysts illustrating their applicability.

The stability of metal organic frameworks (MOFs) in a water-rich environment is a topic of significant importance, especially for adsorption and water purification applications. MIL-88A containing iron ions and fumaric acid ligands, was synthesized through a water-based viable strategy. The robustness of MIL-88A in aqueous solutions was studied experimentally, through evaluating the chemical, thermal, and hydrolytic stability of this compound by varying the conditions and properties of aqueous solutions. Different characterization techniques were employed to explore the features of the synthesized MIL-88A such as XRD, SEM, FTIR, TGA, UV–vis DRS, zeta potential, and MP-AES measurements. The electronic structure was studied on a model nanocrystal with density functional theory (DFT) calculations. The MIL-88A structure was drastically affected in basic medium as confirmed by the characterization techniques used. MIL-88A became completely amorphous upon exposure to boiling water. The hydrolytic stability results showed that MIL-88A loses gradually its structural integrity in each water cycle.

A combination of transient methods in a laboratory-scale trickle bed reactor and attenuated total reflection (ATR)-infrared spectroscopy was applied to gain insight into the reaction mechanism of the direct synthesis of hydrogen peroxide (DSHP) on a commercial 5 %Pd/C catalyst, with water and methanol used as solvents. During the transient studies, after the switch from water to methanol, an oscillatory pattern was observed in which methoxy and hydroxymethyl species were observed prior to the peroxide species. From the specific position and the maxima in the intensities of these species over time, an augmented reaction scheme for the DSHP in methanol was proposed, in which methanol can form hydroxymethyl species which act as co-catalysts to reduce absorbed oxygen species.

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, oxide 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.

Kinetic analysis of the gas-phase and liquid phase hydrogenation of toluene to methylcyclohexane on Ni catalysts was performed. For complex reaction mechanisms comprising several kinetically significant steps, nonlinear regression, while giving an adequate description of experimental data, leads to kinetic parameters which are poorly defined. The approach based on Bayesian statistics allows identification of the values of such parameters which are the most statistically probable.

Ibuprofen (IBU) and diclofenac (DCF) are non-steroidal anti-inflammatory pharmaceuticals. They are frequently detected in wastewater and in the environment. Due to their harmful effect on aquatic o...

The synthesis of propylene oxide from propylene and hydrogen peroxide and the side reactions of propylene oxide were studied in a broad range of experimental conditions (25–80 °C, 2.5–8.5 bar) in a...

Sugar monomers originating from well-controlled hydrolysis of hemicelluloses appearing in biomass are important platform molecules and they can be further valorized by catalytic hydrogenation, oxid...

Oxidation of a mixture of glucose and arabinose over 1% Au deposited on alumina was investigated in a semi-batch reactor varying pH, temperature and partial pressure of oxygen. Elevation of the latter enhancing the rate induced also losses in selectivity to aldonic acids. A kinetic model representing the catalytic oxidation reactions of arabinose and glucose along with respective isomerization to fructose and ribulose was developed. Calculations based on the model were able to describe experimental data in a reliable way.

Developing a structured catalyst was performed successfully and ruthenium catalysts supported by carbon-coated aluminum foams were prepared. Seven different characterization techniques such as SEM,...

Furfural oxidation with hydrogen peroxide was performed using sulfated zirconia as an acid catalyst within the temperature range of 40–90 °C. The catalytic behavior of sulfated zirconia due to its ...

Carbamazepine (CBZ) is a recalcitrant pharmaceutical often detected in wastewater and in the environment. CBZ can be removed from wastewater through advanced oxidation treatment methods such as ozonation. In this study, CBZ and its transformation product 1-(2-benzaldehyde)-(1H,3H)-quinazoline-2,4-dione (BQD) were ozonated, and the formation and transformation of their ozonation products were investigated using liquid chromatography coupled to ion trap mass spectrometry and high-resolution mass spectrometry as well as nuclear magnetic resonance (NMR). The main products, 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one (BQM) and BQD were quantified using isolated standards and LC-UV. Of the original CBZ concentration, 74% was transformed into BQM and 83% of BQM was further transformed into BQD. Both products are more stable than CBZ and could still be detected after 240 min of ozonation. Another major product, 2,2′-azanediyldibenzaldehyde (TP225) was for the first time identified using NMR. Twelve further CBZ products were identified. Electronic supplementary material The online version of this article (10.1007/s11356-020-08795-0) contains supplementary material, which is available to authorized users.

Aqueous phase reforming (APR) of xylose and xylitol was studied over Pt/Pd catalysts supported on mesoporous carbon (Sibunit) in the temperature range 175–225 °C in a laboratory-scale packed bed reactor. Formic acid was introduced to the reaction mixture to simulate an industrial feedstock from the reactive extraction of hemicelluloses from biomass. The conversion was higher in xylose APR, however, xylitol APR displayed a higher selectivity to hydrogen and stable operation under the conditions investigated. Addition of formic acid increased the hydrogen production in the APR of xylitol, while xylose APR displayed an opposite behavior. The ratio of the gas and liquid products was similar for both substrates at an equal conversion, however, the alkane distribution was different, depending on the presence of formic acid and reaction temperature. It can be concluded that the APR of xylitol to hydrogen was successfully conducted with the selected catalyst in the presence of formic acid as a co-reactant.