Successful immobilization of lanthanides doped TiO2 on inert foam for repeatable hydrogen generation from aqueous ammonia

We describe the successful possibility of the immobilization of a photocatalyst on foam, which is beneficial from a practical point of view. An immobilized photocatalyst is possible for use in a continuous experiment and can be easily separated from the reactor after the reaction concludes. Parent TiO2, La/TiO2, and Nd/TiO2 photocatalysts (containing 0.1 wt.% of lanthanide) were prepared by the sol-gel method and immobilized on Al2O3/SiO2 foam (VUKOPOR A) by the dip-coating method. The photocatalysts were investigated for the photocatalytic hydrogen generation from an aqueous ammonia solution under UVA light (365 nm). The evolution of hydrogen was compared with photolysis, which was limited to zero. The higher hydrogen generation was observed in the presence of 0.1 wt.% La/TiO2 than in 0.1 wt.% Nd/TiO2. This is, besides other things, related to the higher level of the conduction band, which was observed for 0.1 wt.% La/TiO2. The higher conduction band's position is more effective for hydrogen production from ammonia decomposition.Web of Science135art. no. 125

The role of fluorine in F-La/TiO2 photocatalysts on photocatalytic decomposition of methanol-water solution

F-La/TiO2 photocatalysts were studied in photocatalytic decomposition water-methanol solution. The structural, textural, optical, and electronic properties of F-La/TiO2 photocatalysts were studied by combination of X-ray powder diffraction (XRD), nitrogen physisorption, Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), Electrochemical impedance spectroscopy (EIS), and X-ray fluorescence (XPS). The production of hydrogen in the presence of 2.8F-La/TiO2 was nearly up to 3 times higher than in the presence of pure TiO2. The photocatalytic performance of F-La/TiO2 increased with increasing photocurrent response and conductivity originating from the higher amount of fluorine presented in the lattice of TiO2.Web of Science1218art. no. 286

Role of lamp type in conventional batch and micro-photoreactor for photocatalytic hydrogen production

The use of an irradiation source with a homogeneous distribution of irradiation in the volume of the reaction mixture belongs to the essential aspects of heterogeneous photocatalysis. First, the efficacy of six lamps with various radiation intensity and distribution characteristics is contrasted. The topic of discussion is the photocatalytic hydrogen production from a methanol-water solution in the presence of a NiO-TiO2 photocatalyst. The second section is focused on the potential of a micro-photoreactor system–the batch reactor with a micro-reactor with a circulating reaction mixture, in which the photocatalytic reaction takes place using TiO2 immobilized on borosilicate glass. Continuous photocatalytic hydrogen generation from a methanol-water solution is possible in a micro-photoreactor. This system produced 333.7 ± 21.1 µmol H2 (252.8 ± 16.0 mmol.m−2, the hydrogen formation per thin film area) in a reproducible manner during 168 h

Evaluation of praying mantis diffuse reflectance accessory to measure the spectra of solid catalysts

Bakalářská práce se zabývá možností využití difusně reflexní spektroskopie v ultrafialové a viditelné oblasti pro analýzu aktivních center pevných katalyzátorů za reakčních podmínek. Teoretická část bakalářské práce se zabývá principem a významem využití této techniky při charakterizaci aktivních center pevných katalyzátorů za reakčních podmínek. Experimentální část bakalářské práce je zaměřena na zhodnocení potenciálu měření difusně reflexních spekter katalyzátorů na bázi železa a vanadu ve vysokoteplotní in-situ cele. Pro oba typy materiálů je pozornost zaměřena na analýzu přínosu měření difusně reflexních spekter ve vysokoteplotní cele s ohledem na typ částic, které je tímto způsobem možné analyzovat. Pozornost je rovněž zaměřena na studium využití difusně reflexních spekter pro popis struktury aktivních částic katalyzátorů na bázi železa a vanadu v průběhu oxidativní dehydrogenace ethanu.Bachelor thesis deals with the possibility of using diffuse reflectance spectroscopy in the ultraviolet and visible light for the analysis of the active species of solid catalysts under reaction conditions. The theoretical part deals with the principle and importance of the use this technique in characterization of the active species of solid catalysts under reaction conditions. The experimental part of the thesis focuses on the evaluation of potential of measuring diffuse reflectance spectra of iron and vanadium based catalysts in the Praying Mantis diffuse reflectance accessory. For both types of materials, attention is focused on the analysis of the contribution of measuring diffuse reflectance spectra in the Praying Mantis diffuse reflectance accessory with regard to the type of particles, which can be analysed by this method. The attention is also focused on the study of the use of diffuse reflectance spectra for describing the structure of the active species of iron and vanadium based catalysts during the oxidative dehydrogenation of ethane.Katedra fyzikální chemieBakalářka přednesla výsledky své bakalářské práce a zodpověděla dotazy členů komise

In-situ characterization of the transformation of Zn-Al hydrotalcites to appropriate mixed oxides active in aldol condensation of furfural

V rámci první části této diplomové práce byla pozornost zaměřena především na popis teplotní transformace Zn-Al hydrotalcitů na Zn-Al směsné oxidy, případně potvrzení vzniku ZnAl2O4 spinelu pomocí in-situ technik. Zn-Al hydrotalcity s teoretickým Zn/Al molárním poměrem v rozmezí 1-5 byly připraveny srážením dusičnanu zinečnatého a dusičnanu hlinitého uhličitanem sodným nebo hydrolyzující močovinou. Reálný Zn/Al molární poměr připravených Zn-Al hydrotalcitů byl stanoven pomocí rentgenové fluorescenční analýzy (XRF). Struktura těchto materiálů byla studována pomocí in-situ spektroskopie v ultrafialové a viditelné oblasti za použití vysokoteplotní reakční cely (DRS) a in-situ rentgenové difrakční analýzy (XRD), čím byly získány důležité informace o postupné tepelné přeměně Zn-Al hydrotalcitů na Zn-Al směsné oxidy. Tyto informace byly doplněny na základě termogravimetrické analýzy (TGA), skenovací elektronové mikroskopie (SEM) a adsorpce kapalného dusíku (N2-BET metody). V druhé části diplomové práce byla pozornost zaměřena na popis složení, struktury a acido-bazických vlastností Zn-Al směsných oxidů připravených z příslušných Zn-Al hydrotalcitů kalcinovaných při teplotě 400 °C. Množství kyselých a bazických center Zn-Al směsných oxidů bylo stanoveno pomocí teplotně programované desorpce amoniaku (TPD-NH3) a teplotně programované desorpce oxidu uhličitého (TPD- CO2). V neposlední řadě byly Zn-Al směsné oxidy studovány v aldolové kondenzaci furfuralu s acetonem.The first part of this master´s thesis was focused mainly on the description of Zn-Al hydrotalcite transformation into Zn-Al mixed oxides or confirmation of formation of ZnAl2O4 spinel by means of in-situ techniques. Zn-Al hydrotalcites with a Zn/Al molar ratio of 1-5 were prepared by precipitation of zinc nitrate and aluminum nitrate with sodium carbonate or hydrolyzing urea. The composition of prepared Zn-Al hydrotalcites was determined by X-ray fluorescence analysis (XRF). The structure of these materials was studied by in-situ ultraviolet and visible spectroscopy using high-temperature reaction cells (DRS) and in-situ X-ray diffraction analysis (XRD) to obtain important information on the gradual thermal conversion of Zn-Al hydrotalcites to Zn-Al mixed oxides. This information was supplemented by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption of liquid nitrogen (N2-BET method). In the second part of the master´s thesis, the attention was focused on description of composition, structure and acid-base properties of Zn-Al mixed oxides prepared from Zn-Al hydrotalcites calcinated at 400 °C. The amount of acidic and basic sites of Zn-Al mixed oxides was determined by temperature programmed desorption of ammonia (TPD-NH3) and temperature programmed desorption of carbon dioxide (TPD-CO2). Activity of Zn-Al mixed oxides was studied in the aldol condensation of furfural with acetone.Fakulta chemicko-technologick

Podporují kovové oxidy Cu aktivitu jako katalyzátoru pro hydrogenolýzu?

The well-established ester hydrogenolysis process has to be further improved to reduce its high energy demand and to replace used Adkins CuCr catalysts by chromium-free alternatives. In this study, the copper-based catalyst was modified by ZnO, ZnO with Al2O3 or MgO to elucidate the metal-oxide influence on catalyst structure, activity, performance and stability in ester hydrogenolysis. The catalysts composition, structure and physico-chemical properties were examined by AAS, XRD, TPR, BET, N2O-RFC, TGA-MS, NH3-TPD and CO2-TPD. It was confirmed that copper itself possesses high intrinsic activity for ester hydrogenolysis but the unpromoted copper species were very unstable. All used metal oxides were proven to be structural promoters stabilizing copper species and increasing the number of active sites. Consequently, they enhanced remarkably catalyst performance in dimethyl adipate conversion despite the decreased intrinsic activity of Cu active sites. All prepared catalysts outperformed a commercial CuCr catalyst in dimethyl adipate hydrogenolysis.Byla studována účinnost modifikovaných Cu katalyzátorů v hydrogenolýze esteru. Modifikace byla provedena pomocí ZnO, ZnO s Al2O3 a MgO. Vliv modifikace na účinnost katalyzátoru a jeho strukturu byl studován metodami AAS, XRD, TPR, BET, N2O-RFC, TGA-MS, NH3-TPD a CO2-TPD

kontrolované odstranění jader siliky z SiO2@MgAl "core-shell" systému jako nástroj pro přípravu dobře orientovaných a vysoce aktivních katalyzátorů

This manuscript presents the preparation of well-oriented @MgAl-layered double hydroxides (LDHs). It extends the reported preparation of SiO2@MgAl-LDH core-shell material (Si/(Si + Mg + Al) molar ratio = 0.54, Mg/Al = 2). There is introduced a new method for the gradual and controlled removal of the SiO2 core from SiO2@MgAl-LDH on treatment with a NaOH solution (1 M) for 1, 2, 4, and 6 h Si/(Si + Mg + Al) molar ratio from 0.06 to 0.52, Mg/Al = 2). Subsequent SiO2 leaching led to empty spheres with properties of the crystalline MgAl-LDH phase preserved. It is proved that @MgAl-LDH spheres formed do not collapse and hence, preserve their orig-inal spherical shape and structural properties. The potential of @MgAl-mixed oxides (MOs) obtained by thermal treatment of @MgAl-LDHs in catalysis is also demonstrated. When this material was used for the aldol condensation reaction of furfural with acetone, the best furfural conversion was obtained for @MgAl-MO with a Si/(Si + Mg + Al) molar ratio of 0.11.Nová metoda kontrolovaného odstranění jader SiO2 z SiO2@MgAl-LDH je představena. Vzniklé prázdné sféry si zachovávají svůj původní tvar a nekolapsují. Připravené materiály jsou testovány jako katalyzátory v aldolové kondenzaci furfuralu. Závislost koverze na molárním poměru Si/(Si+Mg+Al) je diskutována

Vliv kyselých přísad ve furfuralu na účinek MgAl směsných oxidových katalyzátorů v aldolové kondenzaci furfuralu a acetonu

Aldol condensation of furfural and acetone is often used as a model reaction to test acid-base properties of solid catalysts. The present study describes the effect of furfural acidity on the catalytic performance of MgAl mixed oxides. Three furfural sources differing in their acidity were used and compared in aldol condensation at T = 55 ?C and acetone to furfural molar ratio of 10. The furfural conversion over MgAl mixed oxides depended on the acidity of the furfural source, and the catalysts were partially consumed for neutralization of acid admixtures present in furfural. Only for some furfurals could the furfural conversion be improved by distilling the as-received furfural prior to the aldol condensation experiments. Moreover, the storage of the freshly distilled furfural during a few days, even in a closed flask and at a dark place, resulted in a substantial decrease in furfural conversion in aldol condensation. The results indicate that the distillation of the as-received furfural is an effective method to control the performance of basic catalysts at comparable reaction conditions only for some furfurals. Furthermore, the storage of the freshly distilled furfural has to be performed with care to avoid its re-oxidation.Aldolové kondenzace furfuralu a acetonu jsou často používanými modelovými reakcemi pro testování acidobazických vlastností pevných katalyzátorů. Tato studie popisuje vliv kyselosti furfuralu na katalytický účinek MgAl směsných oxidů

Partially Reduced Ni-NiO-TiO₂ Photocatalysts for Hydrogen Production from Methanol–Water Solution

The study compares the photocatalytic behavior of TiO2, NiO-TiO2, and Ni-NiO-TiO2 photocatalysts in photocatalytic hydrogen production from methanol–water solution. TiO2 and NiO-TiO2 photocatalysts with theoretical NiO loading of 0.5, 1.0, and 3.0 wt. % of NiO were prepared by the sol–gel method. The Ni-NiO-TiO2 photocatalysts were prepared by partial reduction of NiO-TiO2 in hydrogen at 450 °C. The Ni-NiO-TiO2 photocatalysts showed significantly higher hydrogen production than the NiO-TiO2 photocatalysts. The structural, textural, redox, and optical properties of all of the prepared photocatalysts were studied by using XRD, SEM, N2- adsorption, XPS, H2-TPR, and DRS. Attention is focused on the contribution of Ni loading, the surface composition (Ni2+, the lattice O2− species, and OH groups), the distribution of Ni species (dispersed NiO species, crystalline NiO phase, and the metallic Ni0 species), oxygen vacancies, TiO2 modification, the TiO2 crystallite size, and the specific surface area