Hydrothermal aging of zeolite-based catalysts

In this study the RE-USY (Davision GO-40) FCC catalyst, a composite of RE-USY zeolite and alumina-silica gel matrix, was treated hydrothermally under simulated FCC regenerator conditions in a laboratory scale fluidized bed. Fresh and steam-aged catalysts were characterized by surface area reduction using the nitrogen BET and t-Plot surface area methods. The surface morphology was apparent from the scanning electron photomicrographs. An irreversible deactivation kinetic model developed earlier by Gardner.; S0- S/S0 ns=Ks t was applied to account for changes of surface area of the zeolite component as a function of time on stream, temperature and steam partial pressure. The kinetic parameters, Ks, the apparent global zeolite hydrothermal stability rate constant and ns, a constant which was determined to be a function of steam partial pressure for a given temperature were determined and compared to those of H-USY (Davision Octacat) FCC catalyst.;An effect of rare-earth exchange on deactivation kinetics was observed. The RE-USY was found to exhibit greater hydrothermal stability than the H-USY determined by the smaller hydrothermal stability rate constant, Ks, and the smaller ns. The presence of rare-earth ions in the zeolite was suggested to prevent extraction of aluminum atoms which caused the hydrothermal destruction of zeolite framework

Metathesis of Ethylene and Trans-2-Butene over MgO Admixed WO3/SiO2 Catalysts

The performances of MgO admixed WO3/SiO2 catalysts were investigated in the cross metathesis of ethylene and 2-butene to propylene at 450oC atmospheric pressure. Compared to the WO3/SiO2 + silica gel, the conversion of 2-butene and the propylene selectivity were much higher on all the WO3/SiO2 + MgO catalysts. An increased propylene yield corresponded to the decrease in 1-butene and cis-2-butene by products. The results in this study also suggest suitable method to prepare highly stable MgO catalysts in order to maximize the propylene yield

Zirconia Modification on Nanocrystalline Titania-Supported Cobalt Catalysts for Methanation

In this present study, the zirconia-modified different crystallite sizes of TiO2 (11, 13 and 16 nm) as support for the cobalt catalysts were investigated. The different TiO2 crystallites derived from the sol-gel method was obtained by varying the water:alkoxide molar ratio from 165 to 4 to gain the different nanocrystallite sizes of TiO2. Then, the TiO2 supports were used to yield various Co/TiO2 catalysts. It was found that the sizes of cobalt oxides species dispersed on TiO2 were corresponding to TiO2 sizes. Based on XPS study, the binding energy of Co 2p3/2 was not affected by the size of TiO2. The catalytic activity was measured via CO hydrogenation under methanation condition. In case of unmodified TiO2 support, the smaller TiO2 crystallites (Co/TiO2_11 nm) exhibited higher activity than other larger ones. Moreover, the zirconia modification also resulted in increased in activity for all samples. For both cases, it can be attributed to increased cobalt dispersion with small crystallite size of TiO2 support coupled with the zirconia modification as measured by CO chemisorption

Formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction

Synthesis of carbon nanostructures at room temperature and under atmospheric pressure is challenging but it can provide significant impact on the development of many future advanced technologies. Here, the formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO(2) reduction reactions (CO(2)RR) are demonstrated. Under a ternary electrolyte system containing [BMIm](+)[BF(4)](−), propylene carbonate, and water, a mixture of sp(2)/sp(3) carbon allotropes were grown on the facets of Ag nanocrystals as building blocks. We show that (i) upon sufficient energy supplied by an electric field, (ii) the presence of negatively charged nascent Ag clusters, and (iii) as a function of how far the C–C coupling reaction of CO(2)RR (10–390 min) has advanced, the growth of nanostructured carbon can be divided into three stages: Stage 1: sp(3)-rich carbon and diamond seed formation; stage 2: diamond growth and diamond–graphite transformation; and stage 3: amorphous carbon formation. The conversion of CO(2) and high selectivity for the solid carbon products (>95%) were maintained during the full CO(2)RR reaction length of 390 min. The results enable further design of the room-temperature production of nanostructured carbon allotropes and/or the corresponding metal-composites by a viable negative CO(2) emission technology

Kinetics of Catalytic Oxidation of Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over LaMn1-xNixO3-d Perovskite Oxide

This present research aims at studying the kinetic reaction of HMF oxidation which is influenced by temperature gradient and Mn/Ni cation ratio in a lanthanum-based perovskite oxide catalyst. The result can be a fruitful database for the further development of the semi-industrial FDCA derivatives production process. Three Mn/Ni cation ratios of LaMnO3-d, LaMn0.5Ni0.5O3-d, and LaNiO3-d catalysts were selected and prepared by the Sol-Gel method. The bulk chemical species and oxidation states of secondary metal elements (Mn and Ni) for all synthesized perovskite-oxide catalysts were characterized by X-ray absorption near edge structure (XANES). The result of the distinct ratio of Mn3+/Mn4+ ions significantly affected the oxidation reaction of HMF. The LaMn0.5Ni0.5O3-d and LaMnO3-d catalysts achieved high catalytic performance for the HMF oxidation reaction at 120 °C for 4 hrs. The kinetic parameters and activation energy were successfully estimated and reported

Catalytic evaluation of Pd-promoted Ni-Co/Al2O3 catalyst for glycerol dry reforming: Assessing hydrogen-rich syngas production, kinetics and mechanisms

The Pd-promoted Ni-Co bimetallic catalysts were prepared using ultrasonic-assisted impregnation, and their performance was subsequently assessed in a fixed-bed reactor. The catalyst's performance was evaluated in glycerol dry reforming (GDR) over a range of temperatures, from 873 K to 1173 K and reactant partial pressures ranging from 10 kPa to 40 kPa. The results indicated that as the temperature was raised from 873 K to 1073 K, there was a noticeable rise in both reactant conversion and product yield. However, beyond 1173 K, catalytic performance declined due to glycerol thermal cracking and sintering of the support at high temperatures, resulting in increased carbon formation. The presence of excessive CO2 was found to suppress glycerol adsorption on the catalyst surface, causing a decline in catalytic activity with a CO2 partial pressure of more than 20 kPa, regardless of reaction temperature. Additionally, excess CO2 were found to enhance the side reaction, particularly reverse water-gas shift (RWGS) that related to produce intermediate H2O. Similarly, the glycerol partial pressure was found to impact catalytic performance, with a decrease in performance beyond 20 kPa due to competing reactants between glycerol and CO2. According to the Langmuir-Hinshelwood kinetic mechanism, a dual molecular adsorption site for glycerol and CO2 was appropriate for this GDR reaction, with an associated activation energy of 47.3 kJ mol−1. The GDR reaction was identified as a kinetically controlled process due to its high activation energy, more than 25 kJ mol−1. The plausible mechanism of GDR over Pd-Ni-Co/Al2O3 occurred through the dissociative-type of adsorption of on active metallic sites of the catalysts for both reactant (glycerol and CO2). This was further facilitated by the bifunctional mechanisms based on H2 generated from dissociative adsorption involving both catalyst's basic sites and metallic active sites. This was ascribed to the highly dispersed and strong interaction between metal-support in Pd-promoted Ni-Co bimetallic catalysts

Synthesis of Cu/TiO2 catalysts by reactive magnetron sputtering deposition and its application for photocatalytic reduction of CO2 and H2O to CH4

© 2019 In the present work, a series of Cu/TiO2 catalysts were successfully synthesized by using pulsed direct current (DC) reactive magnetron sputtering of Cu targets under Ar atmosphere onto various TiO2 supports. The physiochemical properties of the catalysts were characterized by using inductive coupled plasma spectroscopy (ICP), X-ray diffraction (XRD), UV–Vis spectroscopy, N2 physisorption, transmission electron microscopy (TEM), PL spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of all the catalysts were studied via the photocatalytic reduction of CO2 and H2O to CH4 under UV light irradiation. The Cu/TiO2 catalysts exhibited higher photocatalytic activity than the uncoated TiO2 supports and the ones made using an impregnation technique. The electron trapping of copper species, which prolonged the electron-hole recombination process, promoted photocatalytic activity of the Cu-doped catalysts. Moreover, the specific morphologies of the Cu species deposited on TiO2 supports and the smaller change of bandgap energy of the sputter coated catalysts also resulted in an improvement of photocatalytic activity under UV light irradiation

Deposition of Pt nanoparticles on TiO2 by pulsed direct current magnetron sputtering for selective hydrogenation of vanillin to vanillyl alcohol

Pulsed direct current magnetron sputtering (PDC-MSD) was employed for the deposition of Pt nanoparticles (ca. 0.1 wt.%) on anatase TiO2 powder. According to the H2-TPR, XPS, and TEM-EDX results, the characteristics and properties of the deposited nanoparticles depended on the deposition time. During the initial deposition stage (45-90 sec), low-coordinated small spherical Pt nanoparticles were formed. Prolonging the deposition time (135-180 sec), led to the formation of larger Pt nanoparticles, which strongly interacted with the TiO2. The catalytic activities of the prepared Pt/TiO2 with different deposition times in the aqueous phase partial hydrogenation of vanillin to vanillyl alcohol ranged as follows: Pt/TiO2 MSD-45 < Pt/TiO2 MSD-90 < Pt/TiO2 MSD-180 < Pt/TiO2 MSD-135, which was in good agreement with the atomic Pt/Ti ratio and coordinated surface Pt atoms on the catalyst surface. The high catalytic activity of Pt/TiO2 MSD-135 was attributed to the presence of well-dispersed small Pt nanoparticles with more highly-coordinated Pt surface atoms deposited on the TiO2 anatase. PDC-MSD has been proven to be a more effective method for the preparation of supported metal catalysts, compared to those obtained by conventional impregnation technique

Optimization of syngas production via methane bi-reforming using CeO2 promoted Cu/MnO2 catalyst

Currently, syngas plays an important role in renewable and sustainable energy production. The idea of manufacturing syngas via bi-reforming methane, which involves the combination of methane (CH4), carbon dioxide (CO2), and steam, appears very promising. As a result, the goal of this research is to improve syngas output by improving process parameters in methane bi-reforming using a 3%Ce-15%Cu/MnO2 catalyst. Optimization analysis was performed using response surface methodology (RSM). The ultrasonic impregnation (UI) method was employed to synthesize the catalysts used in this study. Following that, the catalyst was characterized using several techniques such as Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD), and temperature programmed oxidation (TPO). The findings of the characterization show that the presence of CeO2 promoters has a dual effect on the size of CuO crystallites. Firstly, it reduces the size from 19.07 nm to 13.66 nm because to the dilutive effect generated by the inclusion of CeO2. Second, the presence of CeO2 promoter accelerates the transition from CuO to Cu0 metallic phase. Furthermore, the addition of CeO2 boosts the CH4 and CO2 conversion rates by 23.65% and 24.93%, respectively. As a result, the H2 yield increases significantly when compared to the unpromoted catalyst. The study investigates the influence of process parameters, specifically the reaction temperature (700–900℃), CO2 ratio (0.2–1), and gas hourly space velocity (GHSV) (16–36 L g cat−1 hr−1), on the conversion of CH4 and CO2, as well as the H2/CO ratio. The optimization study finds that the highest conversion rates for CH4 and CO2 are 78.32% and 72.45%, respectively, when the reaction temperature is 800 °C, the CO2 ratio is 0.6, and the gas hourly space velocity (GHSV) is 26 L g cat−1 hr−1. The optimum conditions result in the highest syngas ratio of 1.77. The results of the optimization are then assessed using the mean errors. The H2/CO ratio, as well as the average errors for CH4 and CO2 conversions, are discovered to be 0.15%, 0.95%, and 0%, respectively