The Effect of CeO2 Preparation Method on the Carbon Pathways in the Dry Reforming of Methane on Ni/CeO2 Studied by Transient Techniques

Molybdenum Modified Sol–Gel Synthesized TiO2 for the Photocatalytic Degradation of Carbamazepine under UV Irradiation

Pharmaceutical CEC compounds are a potential threat to man, animals, and the environment. In this study, a sol–gel-derived TiO2 (SynTiO2) was produced and subsequently sonochemically doped with a 1.5 wt% Mo to obtain the final product (Mo (1.5 wt%)/SynTiO2). The as-prepared materials were characterized for phase structure, surface, and optical properties by XRD, TEM, N2 adsorption–desorption BET isotherm at 77 K, and PSD by BJH applications, FTIR, XPS, and UV-Vis measurements in DRS mode. Estimated average crystallite size, particle size, surface area, pore-volume, pore size, and energy bandgap were 16.10 nm, 24.55 nm, 43.30 m2/g, 0.07 cm3/g, 6.23 nm, and 3.05 eV, respectively, for Mo/SynTiO2. The same structural parameters were also estimated for the unmodified SynTiO2 with respective values of 14.24 nm, 16.02 nm, 133.87 m2/g, 0.08 cm3/g, 2.32 nm, and 3.3 eV. Structurally improved (Mo (1.5 wt%)/SynTiO2) achieved ≈100% carbamazepine (CBZ) degradation after 240 min UV irradiation under natural (unmodified) pH conditions. Effects of initial pH, catalyst dosage, initial pollutant concentration, chemical scavengers, contaminant ions, hydrogen peroxide (H2O2), and humic acid (HA) were also investigated and discussed. The chemical scavenger test was used to propose involved photocatalytic degradation process mechanism of CBZ.

Nanoengineering of Catalysts for Enhanced Hydrogen Production

Hydrogen (H2) has emerged as a sustainable energy carrier capable of replacing/complementing the global carbon-based energy matrix. Although studies in this area have often focused on the fundamental understanding of catalytic processes and the demonstration of their activities towards different strategies, much effort is still needed to develop high-performance technologies and advanced materials to accomplish widespread utilization. The main goal of this review is to discuss the recent contributions in the H2 production field by employing nanomaterials with well-defined and controllable physicochemical features. Nanoengineering approaches at the sub-nano or atomic scale are especially interesting, as they allow us to unravel how activity varies as a function of these parameters (shape, size, composition, structure, electronic, and support interaction) and obtain insights into structure–performance relationships in the field of H2 production, allowing not only the optimization of performances but also enabling the rational design of nanocatalysts with desired activities and selectivity for H2 production. Herein, we start with a brief description of preparing such materials, emphasizing the importance of accomplishing the physicochemical control of nanostructures. The review finally culminates in the leading technologies for H2 production, identifying the promising applications of controlled nanomaterials.

Preparation and Characterization of Supported Molybdenum Doped TiO2 on α-Al2O3 Ceramic Substrate for the Photocatalytic Degradation of Ibuprofen (IBU) under UV Irradiation

TiO2-based photocatalyst materials have been widely studied for the abatement of contaminants of emerging concerns (CECs) in water sources. In this study, 1.5 wt% Mo-doped HRTiO2 was obtained by the sonochemical method. The material was analyzed and characterized for thermal, structural/textural, morphological, and optical properties using TGA-DSC, XRD, TEM, FTIR, XPS, SEM-EDS, BET (N2 adsorption-desorption measurement and BJH application method), and UV-Vis/DRS measurement. By the dip-coating technique, ~5 mg of Mo/HRTiO2 as an active topcoat was deposited on ceramic. In suspension and for photocatalyst activity performance evaluation, 1 g/L of 1.5 wt% (Mo)/HRTiO2 degraded ~98% of initial 50 mg/L IBU concentration after 80 min of 365 nm UV light irradiation and under natural (unmodified) pH conditions. Effects of initial pH condition, catalyst dosage, and initial pollutant concentration were also investigated in the photocatalyst activity performance in suspension. The photocatalyst test on the supported catalyst removed ~60% of initial 5mg/L IBU concentration, while showing an improved performance with ~90% IBU removal employing double and triple numbers of coated disk tablets. After three successive cycle test runs, XRD phase reflections of base TiO2 component of the active photocatalyst supported layer remained unchanged: An indication of surface coat stability after 360 min of exposure under 365 nm UV irradiation.

Rational Design of Non-Precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes

Catalysis is an indispensable part of our society, involved in numerous energy and environmental applications, such as the production of value-added chemicals/fuels, hydrocarbons processing, fuel cells applications, abatement of hazardous pollutants, among others [...]

Modification of the Acyl Chloride Quench-Labeling Method for Counting Active Sites in Catalytic Olefin Polymerization

The reliable and efficient counting of active sites in catalytic olefin polymerization has been realized by using acyl chloride as the quench-labeling agent. However, the molar ratio of acyl chloride to the alkylaluminum cocatalyst must be larger than 1 in order to completely depress side reactions between the quencher and Al-polymeryl that is formed via chain transfer reaction. In this work, a tetrahydrofuran/thiophene-2-carbonyl chloride (THF/TPCC) mixture was used as the quenching agent when counting the active sites of propylene polymerization catalyzed by MgCl2/Di/TiCl4 (Di = internal electron donor)-type Ziegler–Natta catalyst activated with triethylaluminum (TEA). When the THF/TEA molar ratio was 1 and the TPCC/TEA molar ratio was smaller than 1, the [S]/[Ti] ratio of the polymer quenched with the THF/TPCC mixture was the same as that quenched with only TPCC at TPCC/TEA > 1, indicating quench-labeling of all active sites bearing a propagation chain. The replacement of a part of the TPCC with THF did not influence the precision of active site counting by the acyl chloride quench-labeling method, but it effectively reduced the amount of acyl chloride. This modification to the acyl chloride quench-labeling method significantly reduced the amount of precious acyl chloride quencher and brought the benefit of simplifying polymer purification procedures after the quenching step.

Steam reforming of ethanol for hydrogen production: influence of catalyst composition (Ni/Al2O3, Ni/Al2O3–CeO2, Ni/Al2O3–ZnO) and process conditions

Ethanol steam reforming was studied over Ni supported catalysts. The effects of support (Al2O3, Al2O3–ZnO, and Al2O3–CeO2), metal loading, catalyst activation method, and steam-to-ethanol molar feed ratio were investigated. The properties of catalysts were studied by N2 physisorption, TPD-CO2, X-ray diffraction, and temperature programmed reduction. After activity tests, the catalysts were analyzed by TOC analysis. The catalytic activity measurements showed that the addition either of ZnO SSor CeO2 to alumina enhances both ethanol conversion and promotes selectivity towards hydrogen formation. The same effects were observed for catalysts with higher metal loadings. High process temperature and high water-to-ethanol ratio were found to be beneficial for hydrogen production. An extended catalyst stability tests showed no loss of activity over 50 h on reaction stream. The TOC analysis of spent catalysts revealed only insignificant amounts of carbon deposit.

Immobilized TiO2/ZnO Sensitized Copper (II) Phthalocyanine Heterostructure for the Degradation of Ibuprofen under UV Irradiation

Photocatalytic coatings of TiO2/ZnO/CuPc were developed on stainless steel substrates by subsequent sol gel dip coating for TiO2, spray pyrolysis for ZnO, and spin coating for copper (ii) phthalocyanine (CuPc) deposition. The latter compound was successfully prepared using a Schiff-based process. The materials and coatings developed were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy with attached energy dispersive spectroscopy (SEM-EDS), UV-Vis spectroscopy, room temperature photoluminescence (RTPL) spectroscopy, H1-nuclear magnetic resonance (1H-NMR) spectroscopy, C13-nuclear magnetic resonance (13C-NMR) spectroscopy, and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS). The as-deposited TiO2/ZnO/CuPc on stainless steel retained in pristine state the structural and morphological/spectroscopic characteristics of its respective components. Estimated energy band gap values were 3.22 eV, 3.19 eV, 3.19 eV for TiO2, ZnO, TiO2/ZnO respectively and 1.60 eV, 2.44 eV, and 2.92 eV for CuPc. The photocatalytic efficiency of the fabricated TiO2/ZnO/CuPc coatings was tested toward ibuprofen (IBF). After 4 h irradiation under 365 nm UV, an increased degradation of about 80% was achieved over an initial 5 mg/L ibuprofen (IBF). This was much higher compared to about 42% and 18% IBF degradation by TiO2/ZnO and TiO2 thin film, respectively. In all cases, the stability of the best-performing photocatalyst was investigated showing a small decline to 77% of IBF degradation after the 5th cycle run. The effect of pH, reactive oxygen species (ROS) probe, shed light on a possible catalytic mechanism that was suggested.

Hydrothermal Synthesis of ZnO–doped Ceria Nanorods: Effect of ZnO Content on the Redox Properties and the CO Oxidation Performance

The rational design of highly efficient, noble metal-free metal oxides is one of the main research priorities in the area of catalysis. To this end, the fine tuning of ceria-based mixed oxides by means of aliovalent metal doping has currently received particular attention due to the peculiar metal-ceria synergistic interactions. Herein, we report on the synthesis, characterization and catalytic evaluation of ZnO–doped ceria nanorods (NR). In particular, a series of bare CeO2 and ZnO oxides along with CeO2/ZnO mixed oxides of different Zn/Ce atomic ratios (0.2, 0.4, 0.6) were prepared by the hydrothermal method. All prepared samples were characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction (TPR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). The CO oxidation reaction was employed as a probe reaction to gain insight into structure-property relationships. The results clearly showed the superiority of mixed oxides as compared to bare ones, which could be ascribed to a synergistic ZnO–CeO2 interaction towards an improved reducibility and oxygen mobility. A close correlation between the catalytic activity and oxygen storage capacity (OSC) was disclosed. Comparison with relevant literature studies verifies the role of OSC as a key activity descriptor for reactions following a redox-type mechanism.

Effect of the Preparation Method on the Physicochemical Properties and the CO Oxidation Performance of Nanostructured CeO2/TiO2 Oxides

Ceria-based mixed oxides have been widely studied in catalysis due to their unique surface and redox properties, with implications in numerous energy- and environmental-related applications. In this regard, the rational design of ceria-based composites by means of advanced synthetic routes has gained particular attention. In the present work, ceria–titania composites were synthesized by four different methods (precipitation, hydrothermal in one and two steps, Stöber) and their effect on the physicochemical characteristics and the CO oxidation performance was investigated. A thorough characterization study, including N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM) and H2 temperature-programmed reduction (H2-TPR) was performed. Ceria–titania samples prepared by the Stöber method, exhibited the optimum CO oxidation performance, followed by samples prepared by the hydrothermal method in one step, whereas the precipitation method led to almost inactive oxides. CeO2/TiO2 samples synthesized by the Stöber method display a rod-like morphology of ceria nanoparticles with a uniform distribution of TiO2, leading to enhanced reducibility and oxygen storage capacity (OSC). A linear relationship was disclosed among the catalytic performance of the samples prepared by different methods and the abundance of reducible oxygen species.