Project description:Semi-hydrogenation of acetylene in excess ethylene is a key industrial process for ethylene purification. Supported Pd catalysts have attracted most attention due to their superior intrinsic activity but often suffer from low selectivity. Pd single-atom catalysts (SACs) are promising to significantly improve the selectivity, but the activity needs to be improved and the feasible preparation of Pd SACs remains a grand challenge. Here, we report a simple strategy to construct Pd1/TiO2 SACs by selectively encapsulating the co-existed small amount of Pd nanoclusters/nanoparticles based on their different strong metal-support interaction (SMSI) occurrence conditions. In addition, photo-thermo catalysis has been applied to this process where a much-improved catalytic activity was obtained. Detailed characterization combined with DFT calculation suggests that photo-induced electrons transferred from TiO2 to the adjacent Pd atoms facilitate the activation of acetylene. This work offers an opportunity to develop highly stable Pd SACs for efficient catalytic semi-hydrogenation process.
Project description:Monometallic catalysts based on Fe, Ni and Pd, as well as bimetallic catalysts based on Fe-Pd and based on Ni-Pd supported on silica, were synthesized using a sol-gel cogelation process. These catalysts were tested in chlorobenzene hydrodechlorination at low conversion to consider a differential reactor. In all samples, the cogelation method allowed very small metallic nanoparticles of 2-3 nm to be dispersed inside the silica matrix. Nevertheless, the presence of some large particles of pure Pd was noted. The catalysts had specific surface areas between 100 and 400 m2/g. In view of the catalytic results obtained, the Pd-Ni catalysts are less active than the monometallic Pd catalyst (<6% of conversion) except for catalysts with a low proportion of Ni (9% of conversion) and for reaction temperatures above 240 °C. In this series of catalysts, increasing the Ni content increases the activity but leads to an amplification of the catalyst deactivation phenomenon compared to Pd alone. On the other hand, Pd-Fe catalysts are more active with a double conversion value compared to a Pd monometallic catalyst (13% vs. 6%). The difference in the results obtained for each of the catalysts in the Pd-Fe series could be explained by the greater presence of the Fe-Pd alloy in the catalyst. Fe would have a cooperative effect when associated with Pd. Although Fe is inactive alone for chlorobenzene hydrodechlorination, when Fe is coupled to another metal from the group VIIIb, such as Pd, it allows the phenomenon of Pd poisoning by HCl to be reduced.
Project description:We investigated the effects of Pd precursors and preparation methods on the physicochemical properties and performance of Pd/TiO2 catalysts in the photocatalytic degradation of methyl violet. To confirm the influence of the precursors, Pd/TiO2 catalysts were prepared via chemical reduction (CR) using four different Pd precursors. Additionally, to determine the effects of preparation methods, Pd/TiO2 catalysts were fabricated using K2PdCl4 precursor via three different methods: CR, deposition-precipitation (DP), and impregnation. The CO chemisorption results showed that the catalyst prepared via DP using the K2PdCl4 precursor, i.e., Pd/TiO2_K_DP, displayed the highest Pd dispersion of 12.42% owing to the stable formation of Pd(OH)2, which strongly interacted with the -OH groups on the TiO2 support. Although the catalyst prepared via CR using the Pd(NH3)4Cl2·H2O (PA) precursor, i.e., Pd/TiO2_PA_CR, had the lowest Pd dispersion of 0.7%, it exhibited the highest absorption of 26% after 30 min in the dark. It was found that high Pd2+/Pd0 ratio in dark conditions adversely affected the absorption of MV owing to electrostatic repulsion between the cationic dyes and metal nanoparticles. However, the Pd dispersion and the specific surface area played a key role in the photocatalytic activity under UV irradiation. Pd/TiO2_K_CR with higher Pd dispersion showed the highest photocatalytic activity and reaction rate of 0.0212 min-1.
Project description:The synthesis, physicochemical, and functional properties of composite solids resulting from the surface spread of oxidized indium species onto nanoplatelets of anatase were investigated. Both the size and the interaction between the indium- and titanium-containing components control the functional properties. In the reduction of CO2 to CO, the best samples have an indium content between ca. 2 and 5 mol % and showed an excess rate over the photo and thermo-alone processes above 33% and an energy efficiency of 1.3%. Subnanometric (monomeric and dimeric) indium species present relatively weak thermal catalytic response but strong thermo-photo promotion of the activity. A gradual change in functional properties was observed with the growth of the indium content of the solids, leading to a progressive increase of thermal activity but lower thermo-photo promotion. The study provides a well-defined structure-activity relationship rationalizing the dual thermo-photo properties of the catalysts and establishes a guide for the development of highly active and stable composite solids for the elimination and valorization of CO2.
Project description:Converting hydrocarbons and greenhouse gases (i.e., carbon dioxide, CO2) directly into electricity through fuel cells at intermediate temperatures (450 to 550 °C) remains a significant challenge, primarily due to the sluggish activation of C-H and C=O bonds. Here, we demonstrated a unique strategy to address this issue, in which light illumination was introduced into the thermal catalytic CO2 reforming of ethane in the anode as a unique thermo-photo anode process for carbonate-superstructured solid fuel cells. The light-enhanced fuel activation led to excellent cell performance with a record-high peak power density of 168 mW cm-2 at an intermediate temperature of 550 °C. Furthermore, no degradation was observed during ~50 h operation. Such a successful integration of photo energy into the fuel cell system provides a new direction for the development of efficient fuel cells.
Project description:The direct synthesis of hydrogen peroxide (H2O2) from molecular H2 and O2 offers an attractive, decentralized alternative to production compared to the current means of production, the anthraquinone process. Herein we evaluate the performance of a 0.5%Pd-4.5%Ni/TiO2 catalyst in batch and flow reactor systems using water as a solvent at ambient temperature. These reaction conditions are considered challenging for the synthesis of high H2O2 concentrations, with the use of sub-ambient temperatures and alcohol co-solvents typical. Catalytic activity was observed to be stable to prolonged use in multiple batch experiments or in a flow system, with selectivities towards H2O2 of 97% and 85%, respectively. This study was carried out in the absence of halide or acid additives that are typically used to inhibit sequential H2O2 degradation reactions showing that this Pd-Ni catalyst has the potential to produce H2O2 selectively. This article is part of a discussion meeting issue 'Science to enable the circular economy'.
Project description:The group "beyond Li-ion" batteries (Na/Mg-ion batteries) have the advantages of abundant reserves and high theoretical specific capacity. However, the sluggish kinetics resulting from large ion radius (Na+) and polarity (Mg2+) seriously limit the battery performance. Herein, we prepared Nb-doped anatase TiO2 with Ti vacancies (Nb-TiO2) through a simple solvothermal and subsequent calcination process. The Nb doping widens the channels for metal ion diffusion, and the cationic vacancies can act as ion storage sites and improve the electrode conductivity. Thus, Nb-TiO2 exhibits improved performance for rechargeable Na/Mg-ion batteries.
Project description:In this work, the (Y0.5Nb0.5)xTi1-xO2 (x = 0.001, 0.01, 0.02, 0.04, 0.06 and 0.1) ceramics (as called YNTO) were fabricated by synthesized through a standard solid-state reaction. As revealed by the X-ray diffraction (XRD) spectra, the YNTOs exhibit tetragonal rutile structure. Meanwhile, the grain size of YNTO ceramics increased and then decreased with the increase of x value, and the largest value reached when x = 0.02. All the YNTO samples display colossal permittivity (~102-105) over a wide temperature and frequency range. Moreover, the optimal ceramic, (Y0.5Nb0.5)0.02Ti0.98O2, exhibits high performance over a broad temperature range from 20 °C to 180 °C; specifically, at 1 kHz, the dielectric constant and dielectric loss are 6.55 × 104 and 0.22 at room temperature, and they are 1.03 × 105 and 0.11 at 180 °C, respectively.
Project description:Palladium complexes with one N-heterocyclic carbene (NHC) and a pyridine ancillary ligand are powerful cross-coupling precatalysts. Herein, we report such complexes with a cyclic (alkyl)(amino)carbene (CAAC) ligand replacing the NHC. We find that the alleged reduced form, (CAAC)Pd(py), disproportionates to the (CAAC)2Pd0 complex and palladium nanoparticles. This notwithstanding, they are potent catalysts in the Buchwald-Hartwig amination with aryl chlorides under mild conditions (60 °C). In the presence of dioxygen, these complexes catalyze the formation of diazenes from anilines. The catalytic activities of the NHC- and CAAC-supported palladium(0) and palladium(II) complexes are similar in the cross-coupling reaction, yet the CAAC complexes are superior for diazene formation.
Project description:For the application of formic acid as a liquid organic hydrogen carrier, development of efficient catalysts for dehydrogenation of formic acid is a challenging topic, and most studies have so far focused on the composition of metals and supports, the size effect of metal nanoparticles, and surface chemistry of supports. Another influential factor is highly desired to overcome the current limitation of heterogeneous catalysis for formic acid decomposition. Here, we first investigated the effect of support pore structure on formic acid decomposition performance at room temperature by using mesoporous silica materials with different pore structures such as KIE-6, MCM-41, and SBA-15, and achieved the excellent catalytic activity (TOF: 593 h-1) by only controlling the pore structure of mesoporous silica supports. In addition, we demonstrated that 3D interconnected pore structure of mesoporous silica supports is more favorable to the mass transfer than 2D cylindrical mesopore structure, and the better mass transfer provides higher catalytic activity in formic acid decomposition. If the pore morphology of catalytic supports such as 3D wormhole or 2D cylinder is identical, large pore size combined with high pore volume is a crucial factor to achieve high catalytic performance.