The electronic and structural differences of anatase TiO2 (TiO2-A) and rutile TiO2 (TiO2-R) supported Ni catalysts are studied to understand the distinctively different catalytic pathways in guaiacol hydrodeoxygenation over Ni/TiO2-A and Ni/TiO2-R catalysts. Temperature programmed reduction profiles of NiO/TiO2-A and NiO/TiO2-R reveal two types of metal–support interactions. NiO on TiO2-R requires much higher temperature to reduce than NiO on TiO2-A by hydrogen reduction. Surface TiO2-A is partially reduced together with NiO at low temperature driven by strong interaction between reduced Ni and the reducible TiO2-A surface. In situ X-ray photoelectron spectroscopy (XPS), high resolution TEM (HRTEM), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of adsorbed CO reveal two types of reduced Ni species on Ni/TiO2-A: Ni0 particles and atomically dispersed electron-rich Niδ− atoms. While Ni0 particles are formed only at high Ni loadings, they are fully encapsulated by an overlayer of partially reduced TiOx, making the surface of Ni particles totally inaccessible to CO and to reactants. The electron-rich Niδ− atoms are favorably formed at all Ni loadings on the TiO2-A surface and show only linearly adsorbed CO in the DRIFT spectra. Electron transfer from Ti and O on the TiO2-A surface to atomically dispersed Ni is indicated by the observation of dominant electron-rich Niδ− species in conjunction with Ti(4+δ)+ and O(2−δ)− on Ni/TiO2-A following H2 reduction. In contrast, the chemical states of metallic Ni0 and Ti4+ remain unchanged on Ni/TiO2-R after H2 reduction. The atomically dispersed Niδ− species, formed only on the Ni/TiO2-A surface, is proposed as the active site responsible for the selective hydrodeoxygenation of guaiacol to phenolics. In contrast, the metallic Ni0 particles formed on the Ni/TiO2-R surface catalyze the typical catalytic hydrogenation, preferentially saturating the aromatic ring.
Renzhi Xiong,Fangde Liu,Xiao Xiao,Yanhe Xiao,Baochang Cheng,Shuijin Lei
The photocatalytic reduction of CO 2 over CdS faces significant challenges due to dominant hydrogen evolution competition and inefficient CO 2 activation. Herein, a magnetic cobalt-doping strategy is proposed that fundamentally restructures the surface reaction dynamics of CdS, effectively switching the photocatalytic pathway from H 2 evolution to CO 2 reduction. It is demonstrated that cobalt incorporation markedly suppresses charge recombination while increasing the population of photogenerated electrons available for CO 2 activation. Density functional theory calculations uncover two critical doping effects: an upshifted d-band center that optimizes CO 2 adsorption and activation energetics, and a substantially reduced energy barrier for the formation of rate-determining COOH* intermediate. Crucially, the introduced cobalt species induce pronounced spin polarization, which facilitates the separation of charge carriers. This spin effect can be further amplified under an external magnetic field to improve photocatalytic performance. The synergistic interplay of these effects endows Co-doped CdS with an exceptional CO production rate of 2322.8 μmol g −1 h −1 under visible light irradiation and magnetic field application – a 10.9-fold enhancement over pristine CdS. This work pioneers a novel paradigm that concurrently addressing thermodynamic (reaction pathway), kinetic (energy barrier), and electronic-spin (charge separation) factors, providing new design principles for breaking activity-selectivity trade-offs in photocatalytic CO 2 reduction systems.
The introduction of single-atom catalysts (SACs) into Fenton-like oxidation promises ultrafast water pollutant elimination, but the limited access to pollutants and oxidant by surface catalytic sites and the intensive oxidant consumption still severely restrict the decontamination performance. While nanoconfinement of SACs allows drastically enhanced decontamination reaction kinetics, the detailed regulatory mechanisms remain elusive. Here, we unveil that, apart from local enrichment of reactants, the catalytic pathway shift is also an important cause for the reactivity enhancement of nanoconfined SACs. The surface electronic structure of cobalt site is altered by confining it within the nanopores of mesostructured silica particles, which triggers a fundamental transition from singlet oxygen to electron transfer pathway for 4-chlorophenol oxidation. The changed pathway and accelerated interfacial mass transfer render the nanoconfined system up to 34.7-fold higher pollutant degradation rate and drastically raised peroxymonosulfate utilization efficiency (from 61.8% to 96.6%) relative to the unconfined control. It also demonstrates superior reactivity for the degradation of other electron-rich phenolic compounds, good environment robustness, and high stability for treating real lake water. Our findings deepen the knowledge of nanoconfined catalysis and may inspire innovations in low-carbon water purification technologies and other heterogeneous catalytic applications.
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