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Deposition of Pd, Pt, and PdPt Nanoparticles on TiOsub.2 Powder Using Supercritical Fluid Reactive Deposition: Application in the Direct Synthesis of Hsub.2Osub.2
In this study, we investigated the catalytic properties of mono- and bimetallic palladium (Pd) and platinum (Pt) nanoparticles deposited via supercritical fluid reactive deposition (SFRD) on titanium dioxide (TiO[sub.2]) powder. Transmission electron microscopy analyses verified that SFRD experiments performed at 353 K and 15.6 MPa enabled the deposition of uniform mono- and bimetallic nanoparticles smaller than 3 nm on TiO[sub.2]. Electron-dispersive X-ray spectroscopy demonstrated the formation of alloy-type structures for the bimetallic PdPt nanoparticles. H[sub.2]O[sub.2] is an excellent oxidizing reagent for the production of fine and bulk chemicals. However, until today, the design and preparation of catalysts with high H[sub.2]O[sub.2] selectivity and productivity remain a great challenge. The focus of this study was on answering the questions of (a) whether the catalysts produced are suitable for the direct synthesis of hydrogen peroxide (H[sub.2]O[sub.2]) in the liquid phase and (b) how the metal type affects the catalytic properties. It was found that the metal type (Pd or Pt) influenced the catalytic performance strongly; the mean productivity of the mono- and bimetallic catalysts decreased in the following order: Pd > PdPt > Pt. Furthermore, all catalysts prepared by SFRD showed a significantly higher mean productivity compared to the catalyst prepared by incipient wetness impregnation.
Journal Article
Applied homogeneous catalysis
Adopting a didactic approach at an advanced, masters level, 'Applied Homogeneous Catalysis' provides an array of questions and answers, and features numerous industrial case studies and examples.
Book
Phosphorus Modification of Iron: Mechanistic Insights into Ammonia Synthesis on Fesub.2P Catalyst
Ammonia (NH[sub.3]) is a critical chemical for fertilizer production and a potential future energy carrier within a sustainable hydrogen economy. The industrial Haber–Bosch process, though effective, operates under harsh conditions due to the high thermodynamic stability of the nitrogen molecule (N[sub.2]). This motivates the search for alternative catalysts that facilitate ammonia synthesis at milder temperatures and pressures. Theoretical and experimental studies suggest that circumventing the trade-off between N–N activation and subsequent NHx hydrogenation, governed by the Brønsted–Evans–Polanyi (BEP) relationship, is key to achieving this goal. Recent studies indicate metal phosphides as promising catalyst materials. In this work, a comprehensive density functional theory (DFT) study comparing the mechanisms and potential reaction pathways for ammonia synthesis on Fe(110) and Fe[sub.2]P(001) is presented. The results reveal substantial differences in the adsorption strengths of NHx intermediates, with Fe[sub.2]P(001) exhibiting weaker binding compared to Fe(110). For N–N bond cleavage, multiple competing pathways become viable on Fe[sub.2]P(001), including routes involving the pre-hydrogenation of adsorbed N[sub.2] (e.g., through *NNH*). Analysis of DFT-derived turnover rates as a function of hydrogen pressure (H[sub.2]) highlights the increased importance of these hydrogenated intermediates on Fe[sub.2]P(001) compared to Fe(110) where direct N[sub.2] dissociation dominates. These findings suggest that phosphorus incorporation modifies the ammonia synthesis mechanism, offering alternative pathways that may circumvent the limitations of traditional transition metal catalysts. This work provides theoretical insights for the rational design of Fe-based catalysts and motivates further exploration of phosphide-based materials for sustainable ammonia production.
Journal Article
Improving Visible Light Photocatalysis Using Optical Defects in CoOsub.x-TiOsub.2 Photonic Crystals
The rational design of photonic crystal photocatalysts has attracted significant interest in order to improve their light harvesting and photocatalytic performances. In this work, an advanced approach to enhance slow light propagation and visible light photocatalysis is demonstrated for the first time by integrating a planar defect into CoO[sub.x]-TiO[sub.2] inverse opals. Trilayer photonic crystal films were fabricated through the successive deposition of an inverse opal TiO[sub.2] underlayer, a thin titania interlayer, and a photonic top layer, whose visible light activation was implemented through surface modification with CoO[sub.x] nanoscale complexes. Optical measurements showed the formation of “donor”-like localized states within the photonic band gap, which reduced the Bragg reflection and expanded the slow photon spectral range. The optimization of CoO[sub.x] loading and photonic band gap tuning resulted in a markedly improved photocatalytic performance for salicylic acid degradation and photocurrent generation compared to the additive effects of the constituent monolayers, indicative of light localization in the defect layer. The electrochemical impedance results showed reduced recombination kinetics, corroborating that the introduction of an optical defect into inverse opal photocatalysts provides a versatile and effective strategy for boosting the photonic amplification effects in visible light photocatalysis by evading the constraints imposed by narrow slow photon spectral regions.
Journal Article
Engineering the Electronic Structure towards Visible Lights Photocatalysis of CaTiOsub.3 Perovskites by Cation Co-Doping: A First-Principles Study
Cation-anion co-doping has proven to be an effective method of improving the photocatalytic performances of CaTiO[sub.3] perovskites. In this regard, (La/Ce-N/S) co-doped CaTiO[sub.3] models were investigated for the first time using first-principles calculations based on a supercell of 2 × 2 × 2 with La/Ce concentrations of 0.125, 0.25, and 0.375. The energy band structure, density of states, charge differential density, electron-hole effective masses, optical properties, and the water redox potential were calculated for various models. According to our results, (La-S)-doped CaTiO[sub.3] with a doping ratio of 0.25 (LCOS1-0.25) has superior photocatalytic hydrolysis properties due to the synergistic performances of its narrow band gap, fast carrier mobility, and superb ability to absorb visible light. Apart from the reduction of the band gap, the introduction of intermediate energy levels by La and Ce within the band gap also facilitates the transition of excited electrons from valence to the conduction band. Our calculations and findings provide theoretical insights and solid predictions for discovering CaTiO[sub.3] perovskites with excellent photocatalysis performances.
Journal Article