Biomimetic Au/CeO2 Catalysts Decorated with Hemin or Ferrous Phthalocyanine for Improved CO Oxidation via Local Synergistic Effects.
ABSTRACT: Biomimetic catalysts have drawn broad research interest owing to both high specificity and excellent catalytic activity. Herein, we report a series of biomimetic catalysts by the integration of biomolecules (hemin or ferrous phthalocyanine) onto well-defined Au/CeO2, which leads to the high-performance CO oxidation catalysts. Strong electronic interactions among the biomolecule, Au, and CeO2 were confirmed, and the CO uptake over hemin-Au/CeO2 was roughly about 8 times greater than Au/CeO2. Based on the Au/CeO2(111) and hemin-Au/CeO2(111) models, the density functional theory calculations reveal the mechanisms of the biomolecules-assisted catalysis process. The theoretical prediction suggests that CO and O2 molecules preferentially bind to the surface of noncontacting Au atoms (low-coordinated sites) rather than the biomolecule sites, and the accelerating oxidation of Au-bound CO occurs via either the Langmuir-Hinshelwood mechanism or the Mars-van Krevelen mechanism. Accordingly, the findings provide useful insights into developing biomimetic catalysts with low cost and high activity.
Project description:Three morphology-controlled CeO₂, namely nanorods (NRs), nanocubes (NCs), and nanopolyhedra (NPs), with different mainly exposed crystal facets of (110), (100), and (111), respectively, have been used as supports to prepare Ru (3 wt.%) nanoparticle-loaded catalysts. The catalysts were characterized by H₂-temperature programmed reduction (H₂-TPR), CO⁻ temperature programmed desorption (CO-TPD), N₂ adsorption⁻desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (XDS). The characterization results showed that CeO₂-NRs, CeO₂-NCs, and CeO₂-NPs mainly expose (110), (100) and (111) facets, respectively. Moreover, CeO₂-NRs and CeO₂-NCs present higher oxygen vacancy concentration than CeO₂-NPs. In the CO₂ reforming of methane reaction, Ru/CeO₂-NR and Ru/CeO₂-NC catalysts showed better catalytic performance than Ru/CeO₂-NPs, indicating that the catalysts with high oxygen vacancy concentration are beneficial for promoting catalytic activity.
Project description:The redox pretreatment of samples is one of the crucial ways of altering the catalytic properties of the supported noble metal materials in many heterogeneous reactions. Here, H?-reducing pretreatment is reported to enhance the thermal stability of Au-CeO? catalysts prepared by the deposition?precipitation method and calcination at 600 °C for CO oxidation. In order to understand the improved activity and thermal stability, a series of techniques were used to characterize the physico-chemical changes of the catalyst samples. H? pretreatment may lead to: (i) a strong metal?support interaction (SMSI) between Au nanoparticles (NPs) and CeO?, evidenced by the particular coverage of Au NPs by CeO?, electronic interactions and CO adsorption changes. (ii) the production of surface bicarbonates which can accelerate CO oxidation. As a result, the H? pretreatment makes the Au NPs more resistant to sintering at high temperature and enhances the CO oxidation activity. Furthermore, this reduction pretreatment strategy may provide a potential approach to enhance the thermal-stability of other supported noble metal catalysts.
Project description:Here, we synthesized a series of Cu/CeO<sub>2</sub> catalysts with different morphology and size, including Cu/CeO<sub>2</sub> nanospheres (Cu/CeO<sub>2</sub>-S), Cu/CeO<sub>2</sub> nanoparticles (Cu/CeO<sub>2</sub>-P), Cu/CeO<sub>2</sub> nanorods (Cu/CeO<sub>2</sub>-R) and flower-like Cu/CeO<sub>2</sub> microspheres (Cu/CeO<sub>2</sub>-F) to systematically explore the structure-activity relationship in CO oxidation. Crucially, the effect of morphology, crystal size, Ce<sup>4+</sup>/Ce<sup>3+</sup> species, oxygen vacancies derived from the removal of lattice oxygen (O<sub>latt</sub>) species in CeO<sub>2</sub> and lattice defect sites on CO activity was revealed through various characterizations. It was clearly discovered that the activity of these catalysts was as follows: Cu/CeO<sub>2</sub>-R?>?Cu/CeO<sub>2</sub>-P?>?Cu/CeO<sub>2</sub>-S?>?Cu/CeO<sub>2</sub>-F, and the Cu/CeO<sub>2</sub>-R catalyst preferentially showed the best catalytic performance with a 90% conversion of CO even at 58?°C, owned the smaller particles size of CeO<sub>2</sub> and CuO, and exhibited the higher concentration of O<sub>latt</sub> species and oxygen vacancies. Besides, it is also verified that the Cu/CeO<sub>2</sub>-F sample exhibited the larger CeO<sub>2</sub> crystal size (17.14?nm), which led to the lower Cu dispersion and CO conversion, even at 121?°C (T<sub>90</sub>). Most importantly, we discovered that the amount of surface lattice defect sites was positively related to the reaction rate of CO. Simultaneously, DFT calculation also demonstrated that the introduced oxygen vacancies in CeO<sub>2</sub> could accelerate the oxidation of CO by the alteration of CO adsorption energy. Therefore, the morphology, the crystal size, the content of oxygen vacancies, as well as lattice defects of Cu/CeO<sub>2</sub> catalyst might work together for CO oxidation reaction.
Project description:Gold (Au) catalysts exhibit a significant size effect, but its origin has been puzzling for a long time. It is generally believed that supported Au clusters are more or less rigid in working condition, which inevitably leads to the general speculation that the active sites are immobile. Here, by using atomic resolution in situ environmental transmission electron microscopy, we report size-dependent structure dynamics of single Au nanoparticles on ceria (CeO<sub>2</sub>) in CO oxidation reaction condition at room temperature. While large Au nanoparticles remain rigid in the catalytic working condition, ultrasmall Au clusters lose their intrinsic structures and become disordered, featuring vigorous structural rearrangements and formation of dynamic low-coordinated atoms on surface. Ab initio molecular-dynamics simulations reveal that the interaction between ultrasmall Au cluster and CO molecules leads to the dynamic structural responses, demonstrating that the shape of the catalytic particle under the working condition may totally differ from the shape under the static condition. The present observation provides insight on the origin of superior catalytic properties of ultrasmall gold clusters.
Project description:Ultrafine Pt nanoparticles loaded on ceria (CeO<sub>2</sub>) are promising nanostructured catalysts for many important reactions. However, such catalysts often suffer from thermal instability due to coarsening of Pt nanoparticles at elevated temperatures, especially for those with high Pt loading, which leads to severe deterioration of catalytic performances. Here, a facile strategy is developed to improve the thermal stability of ultrafine (1-2 nm)-Pt/CeO<sub>2</sub> catalysts with high Pt content (?14 wt%) by partially embedding Pt nanoparticles at the surface of CeO<sub>2</sub> through the redox reaction at the solid-solution interface. Ex situ heating studies demonstrate the significant increase in thermal stability of such embedded nanostructures compared to the conventional loaded catalysts. The microscopic pathways for interparticle coarsening of Pt embedded or loaded on CeO<sub>2</sub> are further investigated by in situ electron microscopy at elevated temperatures. Their morphology and size evolution with heating temperature indicate that migration and coalescence of Pt nanoparticles are remarkably suppressed in the embedded structure up to about 450 °C, which may account for the improved thermal stability compared to the conventional loaded structure.
Project description:The growth morphology and structure of ceria nano-islands on a stepped Au(788) surface has been investigated by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Within the concept of physical vapor deposition, different kinetic routes have been employed to design ceria-Au inverse model catalysts with different ceria nanoparticle shapes and arrangements. A two-dimensional superlattice of ceria nano-islands with a relatively narrow size distribution (5 ± 2 nm²) has been generated on the Au(788) surface by the postoxidation method. This reflects the periodic anisotropy of the template surface and has been ascribed to the pinning of ceria clusters and thus nucleation on the fcc domains of the herringbone reconstruction on the Au terraces. In contrast, the reactive evaporation method yields ceria islands elongated in [01-1] direction, i.e., parallel to the step edges, with high aspect ratios (~6). Diffusion along the Au step edges of ceria clusters and their limited step crossing in conjunction with a growth front perpendicular to the step edges is tentatively proposed to control the ceria growth under reactive evaporation conditions. Both deposition recipes generate two-dimensional islands of CeO₂(111)-type O-Ce-O single and double trilayer structures for submonolayer coverages.
Project description:We investigate the possibility of functionalizing Au tips by N<sub>2</sub>O molecules deposited on a Au(111) surface and their further use for imaging with submolecular resolution. First, we characterize the adsorption of the N<sub>2</sub>O species on Au(111) by means of atomic force microscopy with CO-functionalized tips and density functional theory (DFT) simulations. Subsequently we devise a method of attaching a single N<sub>2</sub>O to a metal tip apex and benchmark its high-resolution imaging and spectroscopic capabilities using FePc molecules. Our results demonstrate the feasibility of high-resolution imaging. However, we find an inherent asymmetry of the N<sub>2</sub>O probe-particle adsorption on the tip apex, in contrast to a CO tip reference. These findings are consistent with DFT calculations of the N<sub>2</sub>O- and CO tip apexes.
Project description:Nanoparticle (NP) catalysts are widely used for removal of dyes for single use, but there is an acute need for developing catalysts with high efficiency and reusability for mixed dyes. Here we first optimized the process (reactant proportion, temperature, time, and pH) for biosynthesis of monometallic Ag, Au and bimetallic Au-Ag alloy NP catalysts using Polyalthia longifolia leaf extract. The biosynthesized NP catalysts were characterized by UV-vis, DLS, Zeta potential, TEM and EDX study while the probable biomolecules responsible for biosynthesis were identified by FTIR and GC-MS/MS analysis. The NPs are found to be mostly spherical in shape (size 5-20?nm) with prolonged stability. We evaluated their chemo-catalytic performance through degradation of dyes (methyl orange, methyl violet, methylene blue) in individual and ternary mixture in presence of NaBH<sub>4</sub>. The degradation percentage (80.06-96.59% within 5?min), degradation kinetics (k?=?0.361-1.518?min<sup>-1</sup>), half-life (T<sub>50</sub>?=?0.457-1.920?min) and 80% degradation (T<sub>80</sub>?=?1.060-4.458?min) of dyes indicated highest catalytic activity of alloy in ternary mixture. Here we report a unique vacuum filtration system using alloy coated beads with excellent catalytic activity which could be reused thrice for removal of hazardous ternary mixed dyes with great promise for environmental remediation.
Project description:A biomimetic nanochannel coated with a self-assembled monolayer (SAM) can be used for sensing and analyzing biomolecules. The interaction between a transported biomolecule and a SAM governs the mechanically or electrically driven motion of the molecule. To investigate the translocation dynamics of a biomolecule, we performed all-atom molecular dynamics simulations on a single-stranded DNA in a solid-state nanochannel coated with a SAM that consists of octane or octanol polymers. Simulation results demonstrate that the interaction between DNA and a hydrophobic or a hydrophilic SAM is effectively repulsive or adhesive, respectively, resulting in different translocation dynamics of DNA. Therefore, with proper designs of SAMs coated on a channel surface, it is possible to control the translocation dynamics of a biomolecule. This work also demonstrates that traditional tribology methods can be deployed to study a biological or biomimetic transport process.
Project description:In this work, CeO<sub>2</sub> nanosheets decorated with Ag<sub>2</sub>O and AgBr are successfully fabricated via a simple sediment-precipitation method. The as-prepared ternary Ag<sub>2</sub>O/AgBr-CeO<sub>2</sub> composite with double Z-scheme construction was analyzed by various analytical techniques. Ag nanoparticles (NPs) used as the electron medium could reduce the recombination of photoelectrons and holes, thus leading to the improvement of photocatalytic performance of these catalysts. Due to the unique structure and composite advantages, the optimal Ag<sub>2</sub>O/AgBr-CeO<sub>2</sub> photocatalysts exhibit the superior tetracycline (TC) degradation efficiency of 93.23% and favorable stability with near-initial capacity under visible light irradiation. This ternary Z-scheme structure materials will be the well-promising photocatalysts or the purification of antibiotic wastewater.