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Correlation of surface processes with characteristic sensing responses of PdO thin films to ethanol
摘要： Gas sensing characteristics of PdO nanoflake thin films exposed to ethanol (EtOH) at temperatures below 250 °C was studied. The PdO thin film responds distinctly to 0.15 ppm EtOH in dry air at temperatures above 100 °C. A characteristic valley-shaped response feature develops in the early stage of the exposure to EtOH at 150 °C and above. Formation of the valley feature is a result of the combined effects of two types of surface processes, which successively modify the sensor conductance in the opposite way. Dehydrogenation of adsorbed EtOH induces reduction of preadsorbed oxygen anions and the PdO substrate, resulting in the drop of the conductance. On the other hand, subsequent adsorption of EtOH and oxygen on newly growing Pd nanoclusters, which develop due to the reduction of the PdO substrate, causes the increase in the conductance. The Pd nanoclusters can be later reoxidized in the EtOH gas mixture, thereby modifying the sensing behavior of the PdO sensor. X-ray photoelectron spectroscopy (XPS), diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption (TPD) were used to study adspecies and gaseous species formed in the EtOH gas sensing reactions. On the basis of the characteristic electrical response and chemical characterizations, we proposed the formation mechanism for the characteristic response feature.
关键词： Pd nanoclusters,Dehydrogenation,Reduction,PdO,Ethanol,MOS gas sensor
更新于2025-09-23 15:23:52
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Sequential activation of methane by Ir+: An IRMPD and theoretical investigation
摘要： The sequential activation of up to 4 CH4 molecules by Ir+ is investigated through a gas-phase infrared multiple photon dissociation (IRMPD) experiment and theoretical calculations. A molecular beam apparatus was used to generate Ir+ by laser ablation and expose it to controlled amounts of CH4. Product ions were irradiated with IR light from a free electron laser over the 500–1800 cm?1 spectral range and photodissociation was monitored using a time-of-flight mass spectrometer. Experimental spectra were obtained for five distinct species: [Ir,3C,8 H]+, [Ir,3C,10 H]+, [Ir,4C,10 H]+, [Ir,4C,12 H]+, and [Ir,O,3C,12 H]+. To identify these species, B3LYP/def2-TZVPPD geometry optimizations were performed on a variety of possible structures, with computed IR spectra compared to the experimental IRMPD spectra. This has led to the following assignments: [Ir,3C,8 H]+ = IrCH2(CH3)2+, [Ir,3C,10 H]+ = HIr(CH3)3+, [Ir,4C,10 H]+ = Ir(CH3)2(C2H4)+, [Ir,4C,12 H]+ = a mixture of HIr(CH3)(C2H4)+(CH4), HIr(CH3)2(C2H5)+, Ir(CH3)4+, and (H2)Ir(CH3)2(C2H4)+, and [Ir,O,3C,12 H]+ = (H2O)HIr(CH3)3+. Notably, evidence for C C coupling is observed upon reaction with a fourth methane. Mechanisms for the formation of the observed products were also explored computationally by examining the reaction coordinate pathways for the reactions of methane with HIrCH+, IrCH2+, Ir(CH3)2+, HIrCH2(CH3)+, HIr(CH3)3+, and IrCH2(CH3)2+.
关键词： Iridium,Carbon-carbon coupling,Methane activation,Dehydrogenation,Infrared multiple photon dissociation,Reaction coordinate pathway
更新于2025-09-23 15:22:29
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Towards a comprehensive understanding of the Si(100)-2×1 surface termination through hydrogen passivation using methylamine and methanol: a theoretical approach
摘要： Using density functional theory, we explored the termination process of Si (100)-2 × 1 reconstructed surface mechanistically through the dehydrogenation of small molecules, considering methyl amine and methanol as terminating reagents. At first, both the terminating reagents form two types of adduct through adsorption on the Si (100)-2 × 1 surface, one in chemisorption mode and the other via physisorption, from which the dehydrogenation process is initiated. By analyzing the activation barriers, it was observed that termination of the Si-surface through the dehydrogenation is kinetically almost equally feasible using either reagent. We further examined in detail the mechanism for each termination process by analyzing geometrical parameters and natural population analysis charges. From bonding evaluation, it is evident that hydrogen abstraction from adsorbates on the Si-surface is asymmetric in nature, where one hydrogen is abstracted as hydride by the electrophilic surface Si and the other hydrogen is abstracted as proton by the neucleophilic surface Si. Moreover, it was also observed that hydride transfer from adsorbate to the Si-surface occurs first followed by proton transfer. Overall, our theoretical interpretation provides a mechanistic understanding of the Si (100)-2 × 1 reconstructed surface termination by amine and alcohol that will further motivate researchers to design different types of decorated semiconductor devices.
关键词： Bonding evaluation,Si(100)-2 × 1 reconstructed surface,Dehydrogenation,Potential energy surface,Surface termination
更新于2025-09-23 15:21:01
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Synthesis and Characterization of DPP-Based Conjugated Polymers via Dehydrogenative Direct Alkenylation Polycondensation
摘要： Two π-conjugated polymers were successfully synthesized by polycondensation via dehydrogenative direct alkenylation with Pd(II) catalyst (Pd(OAc)2) without directing groups in an atom- and step-economical and eco-friendly manner. Using the Pd(OAc)2/pyridine catalytic system, C-H activation of the C-5 position on the thiophene moiety of 3,6-di(thiophen-2'-yl)diketopyrrolopyrrole derivative was regioselective and the cross-coupled products were readily formed with trans-configuration. The optical, electrochemical, and thermal properties of the synthesized polymers were studied to investigate their potential applicability to semiconducting materials.
关键词： direct alkenylation,palladium,dehydrogenation,diketopyrrolopyrrole,polycondensation
更新于2025-09-19 17:15:36
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Tailoring the surface structure of silicon carbide support for copper catalyzed ethanol dehydrogenation
摘要： The production of acetaldehyde through biomass-derived ethanol dehydrogenation is a sustainable alternative compared to the fossil-feedstock based process, for which Cu-based catalysts are considered to be the most efficient. Herein, we modified the surface of silicon carbide (SiC) to alter the properties of the interface from SiO2-rich to C-rich, and we prepared a series of Cu-supported catalysts (Cu/SiC, Cu/SiO2/SiC, and Cu/C/SiC) with the aim of insight into the effect of the interface structure and composition on catalytic dehydrogenation of ethanol. At 280 °C, the Cu/SiO2/SiC catalyst exhibits high ethanol conversion due to the excellent dispersion of Cu nanoparticles promoted by SiO2-rich interface. In contrast, Cu nanoparticles dispersed on C/SiC shows somewhat lower activity but excellent acetaldehyde selectivity with trace amounts of by-products under identical reaction conditions. This difference is attributed to the fast removal of acetaldehyde because of its low affinity for the relatively inert C-rich interface (C/SiC). This work provides an in-depth understanding of Cu-Si-C multi-interfacial structure and the ethanol dehydrogenation behavior, which may shed light on the design of novel catalysts with tailored interfacial structures.
关键词： dehydrogenation,ethanol,SiC,copper,surface structure
更新于2025-09-10 09:29:36
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Adsorption and decomposition of metal decorated phosphorene toward H2S, HCN and NH3 molecules
摘要： We have studied the adsorption and decomposition of several poisonous gases (H2S, HCN and NH3) on metal (Li, Mg, Al, Ni and Pt) absorbed phosphorene by means of density functional theory. The results indicate Pt-decorated phosphorene has the strongest adsorption capacity for H2S due to the maximum adsorption energy of -1.101 eV in all possible structures of H2S on metal-decorated phosphorene. HCN and NH3 could be e?ectively captured by Al and Ni-decorated phosphorene with large adsorption energies of -2.166 and -1.284 eV, respectively. Considering the low price and more friendly environment of Al light metal, the strong adsorption ability of HCN shows that Al-decorated phosphorene is very promising to remove toxic gases. The energy barrier of the ?rst dehydrogenation for poisonous gases on metal decorated phosphorene is relatively low, which shows the dissociation process is favorable, while the second dehydrogenation has a higher energy barrier, suggesting the decomposition process is di?cult to occur.
关键词： The second dehydrogenation,The ?rst dehydrogenation,Toxic gases
更新于2025-09-04 15:30:14
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Mobility Enhancement in Polycrystalline Silicon Thin Film Transistors due to the Dehydrogenation Mechanism
摘要： We investigated the mechanism of mobility enhancement after the dehydrogenation process in polycrystalline silicon (poly-Si) thin films. The dehydrogenation process was performed by using an in-situ CVD chamber in a N2 ambient or an ex-situ furnace in air ambient. We observed that the dehydrogenated poly-Si in a N2 ambient had a lower oxygen concentration than the dehydrogenated poly-Si annealed in an air ambient. The in-situ dehydrogenation increased the (111) preferred orientation of poly-Si and reduced the oxygen concentration in poly-Si thin films, leading to a reduction of the trap density near the valence band. This phenomenon gave rise to an increase of the field-effect mobility of the poly-Si thin film transistor.
关键词： Low-temperature poly silicon,Crystallization,Dehydrogenation,Thin film transistor
更新于2025-09-04 15:30:14