Experimental studies of strong dipolar interparticle interaction in monodisperse Fe3O4 nanoparticles

Interparticle interaction of monodisperse Fe3 O4 nanoparticles has been experimentally investigated by dispersing the nanoparticles in solvents. With increasing the interparticle distances to larger than 100 nm in a controlled manner, the authors found that the blocking temperature (TB) of the nanoparticles drops continuously and eventually gets saturated with a total drop in TB of 7-17 K observed for 3, 5, and 7 nm samples, compared with their respective nanopowder samples. By carefully studying the dependence of TB on the interparticle distance, the authors could demonstrate that the experimental dependence of TB follows the theoretical curve of the dipole-dipole interaction. © 2007 American Institute of Physics.open313

Zeolitic Imidazolate Framework Decorated Molybdenum Carbide Catalysts for Hydrodeoxygenation of Guaiacol to Phenol

Bimetallic zeolitic imidazolate framework (BMZIF)-decorated Mo carbide catalysts were designed for the catalytic hydrodeoxygenation of guaiacol to produce phenol with high selectivity. A uniform layer of BMZIF was systematically coated onto the surface of the MoO3 nanorods. During carbonization at 700 degrees C for 4 h, BMZIF generated active species (ZnO, CoO) on highly dispersed N-doped carbons, creating a porous shell structure. Simultaneously, the MoO3 nanorod was transformed into the Mo2C phase. The resulting core@shell type Mo2C@BMZIF-700 degrees C (4 h) catalyst promoted a 97% guaiacol conversion and 70% phenol selectivity under 4 MPa of H-2 at 330 degrees C for 4 h, which was not achieved by other supported catalysts. The catalyst also showed excellent selective cleavage of the methoxy group of lignin derivatives (syringol and vanillin), which makes it suitable for selective demethoxylation in future biomass catalysis. Moreover, it exhibits excellent recyclability and stability without changing the structure or active species

Boosting hot electron flux and catalytic activity at metal-oxide interfaces of PtCo bimetallic nanoparticles

Despite numerous studies, the origin of the enhanced catalytic performance of bimetallic nanoparticles (NPs) remains elusive because of the ever-changing surface structures, compositions, and oxidation states of NPs under reaction conditions. An effective strategy for obtaining critical clues for the phenomenon is real-time quantitative detection of hot electrons induced by a chemical reaction on the catalysts. Here, we investigate hot electrons excited on PtCo bimetallic NPs during H-2 oxidation by measuring the chemicurrent on a catalytic nanodiode while changing the Pt composition of the NPs. We reveal that the presence of a CoO/Pt interface enables efficient transport of electrons and higher catalytic activity for PtCo NPs. These results are consistent with theoretical calculations suggesting that lower activation energy and higher exothermicity are required for the reaction at the CoO/Pt interfac

Selective phase transformation of layered double hydroxides into mixed metal oxides for catalytic CO oxidation

Phase transformation from layered double hydroxides (LDHs) into mixed metal oxides (MMOs) has been widely used in various catalytic applications owing to its numerous advantages over conventional synthesis methods. Herein we report the results of selective phase transformation of LDHs into spinels and delafossites for the preparation of phase-pure MMO catalysts. Pure cuprous delafossites and cupric spinels were selectively obtained through heat treatment of Cu-based LDHs followed by post-treatments. This enabled the study of the crystalline-phase-dependent CO oxidation activity of the MMO catalysts and their physicochemical properties. The spinel catalysts exhibited higher CO oxidation activities, in comparison with those of the delafossites, with greater redox properties and improved active sites for CO adsorption. Although the crystalline phases were derived from the same LDH precursors, the catalytic properties of the end product were greatly influenced by their crystal structures

Determination of active site in mesoporous oxides for catalytic furfural hydrogenation

Determining the active site on the catalyst surface and describing the relevant reaction mechanism is crucial for the development of a better catalyst. Knowing what phase plays a crucial role in the activity and selectivity of the reaction is of paramount importance, especially as the phase can change easily in catalytic reactions at various temperature and pressure conditions. Catalytic hydrogenation is essential for the conversion of biomass derivatives into biofuels and high-value-added chemicals. Herein, we prepared mesoporous transition metal oxides (Co3O4, CuO, and CuCo) as a strong candidate for noble metal-free catalyst for furfural hydrogenation. The crystal structure, porosity, and oxidation state of mesoporous oxide catalysts were characterized to determine which active species played a crucial role in catalytic performance

Nanomaterials for heterogeneous catalytic reaction study in ga-sphase

In recent heterogeneous catalysis, much effort has been made in understanding how the size, shape, and composition of nanoparticles and oxide-metal interfaces affect catalytic performance at the molecular level. In this presentation, gas-phase heterogeneous catalytic reactions are addressed including benzene, toluene, and hexane hydrogenation and carbon monoxide oxidation. It is demonstrated the highest reaction yield, product selectivity, and process stability in catalytic reactions are achieved by determining the critical size, shape, and composition of nanoparticles and by choosing the appropriate oxide support, In situ surface characterization techniques including Near Edge X-ray Absorption Fine Structure (NEXAFS) and Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) are utilized for real-time monitoring of nanoparticle catalysts under reaction conditions, in order to identify molecular factors affecting catalytic activity, selectivity, and stability

Catalytic CO2 Hydrogenation Using Cobalt Ferrite Nanoparticles for Selective Production of Light Olefins

The steady increase of CO2 in the atmosphere owing to the excessive use of fossil fuels is seriously threatening the future of humankind by accelerating climate change. However, catalytic chemistry can turn this harmful greenhouse gas into a renewable source of carbon to provide an alternative feedstock for producing high-value hydrocarbon fuels, chemicals, and polymers as a carbon capture and utilization (CCU) strategy. Among the proposed CCU options, catalytic CO2 hydrogenation is attractive because the process is very similar to the well-established CO hydrogenation. The CO2 hydrogenation process usually involves two consecutive steps: the reverse water???gas shift (RWGS) and subsequent CO hydrogenation reactions. In CO2 hydrogenation over Fe-based catalysts, the Fe3O4 phase catalyzes the RWGS reaction, and its reduced form, the Ha??gg iron carbide (??-Fe5C2) phase, provides active sites for CO hydrogenation and chain growth. To increase the CO2 conversion and light olefin selectivity, various strategies have been used to control the electronic and structural properties of Fe-based catalysts. Here, we synthesized monodisperse Fe3O4 and CoFe2O4 nanoparticles (NPs) with a size of 10???20 nm by the thermal decomposition of metal???oleate complexes and supported them on carbon nanotubes (CNTs). It was found that the Na and Co promoters played decisive roles in controlling the reaction rates and product selectivity of catalytic CO2 hydrogenation over these reduced CoFe2O4 NP/CNT catalysts