Project description:The aim of this study was to obtain nanocrystalline mixed metal-oxide-ZrO₂ catalysts via a sonochemically-induced preparation method. The effect of a stabiliser's addition on the catalyst parameters was investigated by several characterisation methods including X-ray Diffraction (XRD), nitrogen adsorption, X-ray fluorescence (XRF), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and µRaman. The sonochemical preparation method allowed us to manufacture the catalysts with uniformly dispersed metal-oxide nanoparticles at the support surface. The catalytic activity was tested in a methane combustion reaction. The activity of the catalysts prepared by the sonochemical method was higher than that of the reference catalysts prepared by the incipient wetness method without ultrasonic irradiation. The cobalt and chromium mixed zirconia catalysts revealed their high activities, which are comparable with those presented in the literature.
Project description:The vital role of ethylenediaminetetraacetic acid on the structure and the oxygen reduction reaction activity of the non-precious-metal-based pyrolyzed catalyst is reported and elaborated. The resultant catalyst can overtake the performance of commercial Pt/C catalyst in an alkaline medium.
Project description:To investigate the effect of catalyst precursors on physicochemical properties and activity of lean methane catalytic combustion, a series of Co3O4 catalysts were prepared via a precipitation method by using four different cobalt precursors: Co(C2H3O2)2, Co(NO3)2, CoCl2, and CoSO4. The catalysts were characterized by BET, XRD, SEM, Raman, XPS, XRF, O2-TPD and H2-TPR techniques. It was found that the different types of cobalt precursor had remarkable effects on the surface area, particle size, reducibility and catalytic performance. In contrast, the Co3O4-Ac catalyst showed a relatively small surface area, but its activity and stability were the highest. XPS, Raman, O2-TPD and H2-TPR results demonstrated that the superior catalytic performance of Co3O4-Ac was associated with its higher Co2+ concentration, more surface active oxygen species and better reducibility. In addition, the activity of the Co3O4-S catalyst reduced significantly due to the residual impurity SO4 2-, which could reduce the concentration of surface adsorbed active oxygen species and inhibit oxygen migration.
Project description:Molecular catalysts that combine high product selectivity and high current density for CO2 electrochemical reduction to CO or other chemical feedstocks are urgently needed. While earth-abundant metal-based molecular electrocatalysts with high selectivity for CO2 to CO conversion are known, they are characterized by current densities that are significantly lower than those obtained with solid-state metal materials. Here, we report that a cobalt phthalocyanine bearing a trimethyl ammonium group appended to the phthalocyanine macrocycle is capable of reducing CO2 to CO in water with high activity over a broad pH range from 4 to 14. In a flow cell configuration operating in basic conditions, CO production occurs with excellent selectivity (ca. 95%), and good stability with a maximum partial current density of 165 mA cm-2 (at -0.92 V vs. RHE), matching the most active noble metal-based nanocatalysts. These results represent state-of-the-art performance for electrolytic carbon dioxide reduction by a molecular catalyst.
Project description:The effect of chlorine on mercury oxidation and nitrogen oxides (NO x ) reduction over selective catalytic reduction (SCR) catalysts was investigated in this study. Commercial SCR catalysts achieved a high Hg0 oxidation efficiency when Cl2 was sprayed into the flue gas. Results indicated that an appropriate concentration of Cl2 was found to promote NO x reduction and Hg0 oxidation significantly. An optimal concentration of Cl2 (25 ppm) was found to significantly promote NO x reduction and Hg0 oxidation. Moreover, we studied the effects of Cl2 on NO x reduction and Hg0 oxidation over SCR catalysts under different concentrations of SO2. The SO2 poisoning effect was decreased by Cl2 when the SO2 concentration was low (below 1500 ppm). However, sulfate gradually covered the catalyst surface over time during the reaction, which limited the impact of Cl2. Finally, different sulfur-poisoned catalysts were examined in the presence of Cl2. The NO x reduction and Hg0 oxidation performances of sulfate-poisoned catalysts improved when Cl2 was added to the flue gas. Mechanisms for NO x reduction and Hg0 oxidation over fresh catalysts and sulfate-poisoned catalysts in the presence of Cl2 were proposed in this study. The mechanism of Cl2-influenced NO x reduction was similar to that for the NH3-SCR process. With Cl2 in the flue gas, the number of Brønsted active sites increased, which improved catalytic activity. Furthermore, Cl2 reoxidized V4+-OH to V5+=O and caused the NH3-SCR process to operate continuously. The Langmuir-Hinshelwood mechanism was followed for Hg0 oxidation by SCR catalysts when Cl2 was in the flue gas. Cl2 increased the number of Lewis active sites, and catalytic activity increased. Hg0 adsorbed on the surface of the catalysts and was then oxidized to HgCl2. Adding Cl2 to the flue gas increased the strength and number of acid sites on sulfate-poisoned catalysts.
Project description:The synergism of the electronic properties of nickel and cobalt enables bimetallic NiCo complexes to process H2. The nickel-cobalt hydride [(dppe)Ni(pdt)(H)CoCp*]+ ([1H]+ ) arising from protonation of the reduced state 1 was found to be an efficient electrocatalyst for H2 evolution with Cl2CHCOOH, and the oxidized [Ni(ii)Co(iii)]2+ form is capable of activating H2 to produce [1H]+ . The features of stereodynamics, acid-base properties, redox chemistry and reactivity of these bimetallic NiCo complexes in processing H2 are potentially related to the active site of [NiFe]-H2ases.
Project description:Exploring non-precious metal-based catalysts for oxygen reduction reactions (ORR) as a substitute for precious metal catalysts has attracted great attention in recent times. In this paper, we report a general methodology for preparing nitrogen-doped reduced graphene oxide (N-rGO)-supported, FeCo alloy (FeCo@N-rGO)-based catalysts for ORR. The structure of the FeCo@N-rGO based catalysts is investigated using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and transition electron microscopy, etc. Results show that the FeCo alloy is supported by the rGO and carbon that derives from the organic ligand of Fe and Co ions. The eletrocatalytic performance is examined by cyclic voltammetry, linear scanning voltammetry, Tafel, electrochemical spectroscopy impedance, rotate disc electrode, and rotate ring disc electrode, etc. Results show that FeCo@N-rGO based catalysts exhibit an onset potential of 0.98 V (vs. RHE) and a half-wave potential of 0.93 V (vs. RHE). The excellent catalytic performance of FeCo@N-rGO is ascribed to its large surface area and the synergistic effect between FeCo alloy and N-rGO, which provides a large number of active sites and a sufficient surface area.
Project description:Evolution of the Pd active centers in size and spatial distribution leads to an irreversible deactivation in many high-temperature catalytic processes. This research demonstrates the use of a defective alumina (Al2O3-x) as catalyst support to anchor Pd atoms and suppress the growth of Pd clusters in catalytic methane oxidation. A combination of operando spectroscopy and density functional theory (DFT) calculations provide insights into the evolution of Pd species and reveals distinct catalytic methane oxidation mechanisms on Pd single atoms, clusters, and nanoparticles (NPs). Among these Pd species, the cluster active centers are found to be the most favorable participants in methane oxidation due to their high dispersion, high content of Pd2+ oxidation state, and resistance to deactivation by carbonates, bicarbonates, and water. The Pd/Al2O3-x catalyst shows increased stability with respect to a Pd/Al2O3 counterpart during simulated aging in alternating reducing and oxidizing conditions due to stronger interactions with the support. This study demonstrates that defect engineering of non-reducible supports can constrain the evolution of active centers, which holds promising potential for widespread utilization across diverse industrial catalytic processes, including various hydrogenation and oxidation reactions.
Project description:Dry reforming of methane is a promising reaction to convert CO2 and combat climate change. However, the reaction is still not feasible in large-scale industrial applications. The thermodynamic need for high temperatures and the potential of carbon deposition leads to high requirements for potential catalyst materials. As shown in previous publications, the Ni-doped perovskite-oxide Nd0.6Ca0.4Fe0.97Ni0.03O3 is a potential candidate as it can exsolve highly active Ni nanoparticles on its surface. This study focused on controlling the particle size by varying the reduction temperature. We found the optimal temperature that allows the Ni nanoparticles to exsolve while not yet enabling the formation of deactivating CaCO3. Furthermore, the exsolution process and the behaviour of the phases during the dry reforming of methane were investigated using in situ XRD measurements at the DESY beamline P02.1 at PETRA III in Hamburg. They revealed that the formed deactivated phases would, at high temperatures, form a brownmillerite phase, thus hinting at a potential self-healing mechanism of these materials.
Project description:The visible light photocatalytic reduction of CO2 to fuel is crucial for the sustainable development of energy resources. In our present work, we report the synthesis of novel reduced graphene oxide (rGO)-supported C3N4 nanoflake (NF) and quantum dot (QD) hybrid materials (GCN) for visible light induced reduction of CO2. The C3N4 NFs and QDs are prepared by acid treatment of C3N4 nanosheets followed by ultrasonication and hydrothermal heating at 130-190 °C for 5-20 h. It is observed that hydrothermal exposure of acid-treated graphitic carbon nitride (g-C3N4) nanosheets at low temperature generated larger NFs, whereas QDs are formed at higher temperatures. The formation of GCN hybrid materials was confirmed by powder X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy (TEM), and UV-vis spectroscopy. High-resolution TEM images clearly show that C3N4 QDs (average diameter of 2-3 nm) and NFs (≈20-45 nm) are distributed on the rGO surface within the GCN hybrid material. Among the as-prepared GCN hybrid materials, GCN-5 QDs exhibit excellent CO2 reductive activity for the generation of formaldehyde, HCHO (10.3 mmol h-1 g-1). Therefore, utilization of metal-free carbon-based GCN hybrid materials could be very promising for CO2 photoreduction because of their excellent activity and environmental sustainability.