Pulsed-spray Evaporation Chemical Vapor Deposition Research Articles

Insight into one-step synthesis of active amorphous La-Co thin films for catalytic oxidation of CO

Active amorphous lanthanum-based thin films were synthesized through one-step pulsed spray evaporation chemical vapor deposition (PSE-CVD) technique at 320 °C for CO oxidation. The obtained films were characterized in terms of phase, composition and morphological properties. X-ray diffraction (XRD) analysis revealed an amorphous nature of the deposited catalysts; and scanning electron microscope (SEM) showed a transition of morphology due to Co doping from sharp to round shaped edges. Chemical composition analysed by EDS and XPS disclose similar trends in amount of cobalt increment and lanthanum decrement. XPS deconvolution revealed pure lanthanum sample (La100) constitutes mainly of lanthanum oxide and lanthanum hydroxide; while, doping with 10% of cobalt (La90Co10) introduces formation of cobalt ions (Co3+ and Co2+) together with La3+ions and low formation of oxygen lattice. Increment of Co to 20% (La80Co20) resulted increasing of Co2+/Co3+, CO32−/OH−formation ratios and oxygen lattice (Olat) content, which may play a key role in the catalytic activity. Complete oxidation of CO was evaluated by online-FTIR. Based on light-off curves, La80Co20 catalyst exhibited the most efficient catalytic activity with T90 of 203 °C, due to increment of lattice oxygen (Olat), Co2+/Co3+ and CO32−/OH−; while, La90Co10 catalyst exhibited lowest catalytic activity which is linked to low Olat and inhibited catalytic effect of water formed at the surface. Thus, the doping strategy of La by Co at low temperature is a good approach for CO abatement. Moreover, DFT calculations demonstrated that amorphous lanthanum oxide is very feasible for CO adsorption.

Support effect on the catalytic activity and stability of non-crystal ternary oxides

Supported film catalysts based oxides were reported as very performant catalysts, and their interactions with the support can enhance the catalytic performance. Here, we report the effect of quite inactive and active substrates on the catalytic activity and stability of non-crystal Fe-Cu-Co ternary thin film oxides deposited on stainless steel mesh (SSM) and copper mesh (CuM) by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) technique, was investigated for CO oxidation. The Fe-Cu-Co ternary oxides thin film was thoroughly characterized in terms of structure, morphology, chemical composition, ionic state and optical properties. The obtained results showed that the catalytic performance and stability depended on the nature of the interphase between the metal substrate and the deposited thin film ternary oxides. The physicochemical properties disclosed the formation of needle-like shaped morphology, which leads to sufficient contact area for surface oxygenated species of ternary oxides, which provided abundant sites for oxygen evolution. Moreover, metallic species (Fe3+, Co3+, Co2+ and Cu2+) and electrophilic oxygenated species (O22− or O-) were confirmed to co-exist at the surface and offered effectual synergetic effects on oxidation reaction with better reducibility. The open porosity of nano-grains, abundance of surface metallic and reactive oxygen species, thermal and electrical conductivities, high reducibility at low temperature due to low optical bandgap energies played together a crucial role in the catalytic oxidation reaction. The ternary oxides exhibited attractive performance towards the total oxidation of CO with a high gas hourly space velocity of 81,818 mL·g-1·h-1. The light-off curves shifted towards lower temperature, when ternary oxides thin film deposited on CuM and used in the reaction. Therefore, the doping strategy of active substrate (in the absence of any other oxygen promoter and noble metals support) is used to adapt highly active transition-metal ternary oxides at low temperature, which could further be a very promising way to significantly increase the activity of ternary oxides for catalytic applications.

Role of copper grid mesh in the catalytic oxidation of CO over one-step synthesized Cu-Fe-Co ternary oxides thin film

The effective valuation of catalyst supports in the catalytic oxidation makes the contribution to understand the support effect of great interest. Here, the role of active substrate in the performance and stability of Cu-Fe-Co ternary oxides was studied towards the complete catalytic oxidation of CO. The Cu-Fe-Co oxide thin films were deposited on copper grid mesh (CUGM) using one-step pulsed-spray evaporation chemical vapor deposition method. Crystalline structure and morphology analyses revealed nano-crystallite sizes and dome-top-like morphology. Synergistic effects between Cu, Fe and Co, which affect the surface Cu2+, Fe3+, Co3+ and chemisorbed oxygen species (O2− and OH−) of thin films over the active support and thus result in better reducibility. The thin film catalysts supported on CUGM exhibited attractive catalytic activity compared to the ternary oxides supported on inert grid mesh at a high gas hourly space velocity. Moreover, the stability in time-on-stream of the ternary oxides on CUGM was evaluated in the CO oxidation for 30 h. The adopted deposition strategy of ternary oxides on CUGM presents an excessive amount of adsorbed active oxygen species that play an important role in the complete CO oxidation. The catalysts supported on CUGM showed better catalytic conversion than that on inert grid mesh and some literature-reported noble metal oxides as well as transition metal oxides counterparts, revealing the beneficial effect of the CUGM support in the improvement of the catalytic performance.

Enhanced property of thin cuprous oxide film prepared through green synthetic route

Thin cuprous oxide films have been prepared by chemical vapor deposition (pulsed spray evaporation-chemical vapor deposition) method without post-treatment. The synthesis of cuprous oxide was produced by applying a water strategy effect. Then, the effect of water on the morphology, topology, structure, optical properties and surface composition of the obtained films has been comprehensively investigated. The results reveal that a pure phase of Cu2O was obtained. The introduction of a small quantity of water in the liquid feedstock lowers the band gap energy from 2.16 eV to 2.04 eV. This finding was mainly related to the decrease of crystallite size due to the effect of water. The topology analyses, by using atomic force microscope, also revealed that surface roughness decreases with water addition, namely more uniform covered surface. Moreover, theoretical calculations based on density functional theory method were performed to understand the adsorption and reaction behaviors of water and ethanol on the Cu2O thin film surface. Formation mechanism of the Cu2O thin film was also suggested and discussed.

Cu-Promoted Cobalt Oxide Film Catalyst for Efficient Gas Emissions Abatement

Thin film catalysts have been recently reported as promising catalysts owing to their good catalytic activity and reduced material amount, leading to low-cost efficient catalysts for gaseous emissions control. Here, we report the slight loading of Cu in cobalt spinel using a one-step pulsed-spray evaporation chemical vapor deposition (PSE-CVD) synthesis technique for efficient short-chain volatile organic compounds (VOCs) emissions treatment. Crystalline structure and morphology analyses revealed nano-crystallite sizes and open-like morphology. The catalytic performance was evaluated through the complete oxidation of C3H6, as a short-chain representative model of VOCs, at a high gas hourly space velocity (GHSV). Very good activity was obtained towards the complete abatement of C3H6 at low temperature and no carbon monoxide (CO) was formed during the oxidation process. Slightly-promoted Co3O4 catalyst with Cu introduction resulted in high catalytic activity comparing to the performance of the catalysts in the literature, due to the high dispersion of Cu and high active surface oxygen amount. Moreover, to evaluate the capability of the used catalysts under near realistic reaction conditions, CO2 effect on the catalytic activity was performed and the catalyst exhibited very good results. Thus, the adopted slightly-doping strategy to tailor a high active catalyst at low temperature could establish a very promising route to strongly enhance the activity of such other catalysts towards gas emissions abatement at low temperature.

CVD synthesis of Cu-doped cobalt spinel thin film catalysts for kinetic study of propene oxidation

A series of Co-Cu binary oxides dispersed homogenously on an inert support were prepared by pulsed-spray evaporation chemical vapor deposition for kinetic study of catalytic combustion. The physicochemical properties of the as-prepared samples were comprehensively characterized in terms of structure, morphology and composition. The results disclosed the formation of cubic binary oxides with amorphous surface. With the progressive introduction of copper into the cobalt spinel, the crystallite size tended to increase due to the incorporation of large Cu2+ ionic radius. Co3+, Co2+, Cu2+, lattice and adsorbed oxygen species were confirmed to co-exist at the surfaces of the binary oxides. The obtained samples exhibited excellent performance for C3H6 oxidation with a high gas hourly space velocity of 150,000 mL·g−1·h−1. The light-off curves shifted towards lower temperature with more Cu incorporation, which was linked to the increase in Co3+/Co2+, and the rearrangement and synergetic effects of Co, Cu and lattice oxygen. The reaction rate increases linearly with the increase in C3H6 concentration by following r=1.12*[C3H6]0.27, without reaching kinetic limitation stage. Moreover, an attractive durability of the binary oxides was observed in the C3H6 oxidation during 50 h. This work provides an inspiration and attractive strategy to develop efficient Co-Cu binary oxides for catalytic applications.

CVD synthesis of cobalt spinel for bio-butanol combustion

As potential substitutes for precious metals, cobalt spinel has been considered as a promising alternative catalyst for the low-temperature catalytic oxidation of biofuels. This work reports the one-step synthesis of cobalt spinel by a more elaborated approach named pulsed-spray evaporation chemical vapor deposition with a new feedstock of Co(acac)3 and toluene. The obtained samples were comprehensively characterized in terms of structure and morphology (XRD, FTIR, Raman and SEM), chemical composition (XPS and EDS) and the redox properties (TPR/TPO). The structural and morphological analysis indicates that the synthesized thin films are pure cubic Co3O4 with homogeneous matrix with well-defined facets and straight edges. Compared to the commonly used feedstock of Co(acac)2/ethanol, Co(acac)3/toluene could result in a much higher growth rate, more lattice oxygen on the surface and better re-oxidation property. The Co3O4 film exhibits attractive performance towards the deep oxidation of n-butanol by preventing the formation of CO and acetaldehyde. The relationship between the peculiar structure and properties of Co3O4 is highlighted. The surface basic sites, specific morphology and the redox properties are proposed to play synergistic roles in the reaction sequence.

SnS2 Nanowall Arrays toward High-Performance Sodium Storage.

Cost-effective sodium ion batteries (SIBs) are emerging as a desirable alternative choice to lithium ion batteries in terms of application in large-scale energy storage devices. SnS2 is regarded as a potential anode material for SIBs because of its unique layered structure and high theoretical specific capacity. However, the development of SnS2 was hindered by the sluggish kinetics of the diffusion process and the inevitable volume change during repeated sodiation-desodiation processes. In this work, SnS2 with a unique nanowall array (NWA) structure is fabricated by one-step pulsed spray evaporation chemical vapor deposition (PSE-CVD), which could be used directly as binder-free and carbon-free anodes for SIBs. The SnS2 NWA electrode achieves a high reversible capacity of 576 mAh g-1 at 500 mA g-1 and enhanced cycling stability. Attractively, an excellent rate capability is demonstrated with ∼370 mAh g-1 at 5 A g-1, corresponding to a capacity retention of 64.2% at 500 mA g-1. The superior sodium storage capability of the SnS2 NWA electrode could be attributed to outstanding electrode design and a rational growth process, which favor fast electron and Na-ion transport, as well as provide steady structure for elongated cycling.

Innovative CVD synthesis of Cu2O catalysts for CO oxidation

The present work reports on a one-step synthesis of thin Cu2O films deposited at 250°C using pulsed-spray evaporation chemical vapor deposition (PSE-CVD). Of interest, water addition (0, 2.5 and 5vol.%) in the liquid feedstock of Cu(acac)2 and ethanol was found to have a significant effect on the catalytic performance of these films towards CO oxidation. The obtained films were comprehensively characterized with X-ray diffraction (XRD), Helium ion microscopy (HIM), X-ray photoelectron spectroscopy (XPS) and Ultraviolet–visible (UV–vis) spectrometry. Both the surface composition and optical properties exhibited good correlation with the catalytic activity. The adopted empirical catalytic screening based on light-off curves measurement demonstrated that Cu2O prepared with 5vol.% of water in the reactant feedstock exhibited the best performance with respect to complete oxidation of CO at 175°C. This finding is reproducible and tentatively attributed to reduced crystallite grain size and more surface oxygen species generated when water was added in the feedstock. Accordingly, the innovative combination of water addition in the feedstock and the use of PSE-CVD technique is expected to assist further synthesis of new efficient thin films paving the way for catalytic applications.

Cobalt-iron oxides made by CVD for low temperature catalytic application

Thin films of cobalt-iron oxides (CoFe2O4) with spinel-type structure were prepared by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) using Fe(acac)3 and Co(acac)3 as precursors. The optimal depositions of CVD-type growth have been established and such growth can be achieved at 400 °C. The obtained films have been systematically characterized in terms of structure (XRD and Raman), surface, and bulk composition (XPS and EDS) as well as morphology (SEM). CoFe2O4 has been successfully tested as an active catalyst toward total oxidation of CO, C3H6, dimethyl ether (DME), and n-C4H8. The results indicate that both the lattice and adsorbed oxygen presented at the surface of the catalyst play determinant roles in the catalytic oxidation process.

CVD synthesis and catalytic combustion application of chromium oxide films

AbstractChromiumoxide (Cr2O3) thin films were controllably synthesized by pulsed‐spray evaporation chemical vapor deposition (PSE‐CVD) for deep oxidation of propene. The effect of substrate temperature on the growth kinetics and morphology of the films was investigated. The prepared samples were comprehensively characterized with respect to structure, morphology and surface composition with XRD, SEM and XPS, respectively. An in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was involved to reveal the surface mechanism occurred on Cr2O3. The growth rate exhibited a linear behavior when the temperature increase from 300 to 450 °C. The structural analysis indicated that a pure phase of Cr2O3 was obtained at 425 °C. The catalytic tests showed that Cr2O3 films prepared on flexible substrates exhibited advantages for the catalytic oxidation of C3H6. Based on the DRIFTS observations, the Langmuir‐Hinshelwood (L‐H) mechanism was proposed for C3H6 over Cr2O3 films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

CVD synthesis of Cu2O films for catalytic application

Pure Cu2O was synthesized at 270 °C by pulsed-spray evaporation chemical vapor deposition.

Tailored synthesis of CoOX thin films for catalytic application

Cobalt oxide thin films were systematically synthesized on an inert carrier by pulsed-spray evaporation chemical vapor deposition (PSE-CVD).

In situ characterization of Cu-Co oxides for catalytic application.

In situ emission and absorption FTIR methods were employed to characterize the spatially resolved structure of binary Co-Cu oxides for low-temperature oxidation of CO and propene. Co-Cu oxide catalysts were controllably synthesized by pulsed-spray evaporation chemical vapor deposition. XRD, FTIR, XPS, UV-vis and helium ion microscopy (HIM) were employed to characterize the as-prepared thin films in terms of structure, composition, optical and thermal properties as well as morphology. In situ emission FTIR spectroscopy indicates that Co3O4, CuCo2O4 and CuO are thermally stable at 650, 655 and 450 °C, respectively. The catalytic tests with absorption FTIR display that the involvement of Co-Cu oxides can initiate CO and C3H6 oxidation at lower temperatures. The results indicate that in situ emission and absorption FTIR are useful techniques to explore the thermal properties and catalytic performance of functional materials, allowing many potential applications in tailoring their temporally and spatially resolved structure-property relationships.

Low-temperature deep oxidation of olefins and DME over cobalt ferrite

This work reports the facile synthesis of cobalt ferrite catalysts by pulsed spray evaporation chemical vapor deposition (PSE-CVD) for low-temperature oxidation of dimethyl ether and olefin exhaust emission. To better understand the structure–performance relationship, the prepared thin films were comprehensively characterized in terms of phases, surfaces and redox properties. A well-crystallized inverse spinel structure was revealed by both XRD and Raman analyses. Helium ion microscopy (HIM) images show that the obtained films have cauliflower structure with apparent open porosity. The catalytic performance of the as-prepared cobalt ferrite was evaluated with a fixed-bed quartz reactor–FTIR system. The results indicate that the cobalt ferrites were very active for the total oxidation of propene, n-butene and DME at low temperature and no CO was observed during the oxidation processes. The attractive performance of cobalt ferrite catalysts is attributed to a redox mechanism which involves the synergistic effect of the morphology, reducibility, and lattice oxygen mobility.

Facile synthesis of catalytically active copper oxide from pulsed-spray evaporation CVD

Copper oxide thin films were controllably synthesized by pulsed-spray evaporation chemical vapor deposition (PSE-CVD). The growth kinetics was investigated by considering the pressure effect. X-ray diffraction, in situ emission Fourier transform infrared spectroscopy, Helium ion microscopy (HIM) and ultraviolet-visible (UV-Vis) spectroscopy were employed to investigate the physicochemical properties of the deposited thin films. A pure phase CuO was confirmed by the structural investigations. The growth rate exhibited a linear increase when the deposition pressure was lower than 24mbar, while further increase of the pressure to 50mbar was observed to have a negligible effect on the growth rate. The optical bandgap energy was estimated to be 1.81±0.05eV. The catalytic performance of copper oxide was evaluated for the deep oxidation of propene with online FTIR as the monitoring technique. The catalytic tests show that CuO films prepared on flexible substrates such as stainless steel mesh exhibit advantages for the catalytic oxidation of propene.

Pulsed-spray evaporation CVD synthesis of hematite thin films for catalytic conversion of CO

Catalytically active thin films of hematite (α-Fe2O3) were synthesized by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) with Fe(acac)3 as the precursor. The obtained films were comprehensively characterized with X-ray diffraction (XRD), emission Fourier transform infrared (FTIR) and Raman spectroscopy, Scanning electron microscopy (SEM), Helium ion microscopy (HIM), Energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and Ultraviolet–Visible (UV–Vis) spectrometry. The catalytic behavior of the prepared α-Fe2O3 thin film towards total oxidation of CO was investigated in a plug-flow reactor. The structural analysis revealed that only the single-phase inverse spinel type α-Fe2O3 was obtained at the deposition temperature of 300°C. The optical band gap energy was estimated to be 2.16±0.05eV. The results showed that α-Fe2O3 can initiate CO oxidation at 230°C, enabling the production of CO2 at much lower temperature compared to the reaction performed without catalyst. It also demonstrated that the hematite thin films prepared here can be competitive to catalysts described in the literature. Both the lattice and adsorbed oxygen detected by XPS were proposed to be consistent with the Eley–Rideal mechanism for CO conversion.

Synthesis of the Catalytically Active Mn3O4 Spinel and Its Thermal Properties

Tetragonal hausmannite (Mn3O4) was synthesized by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) at moderate temperatures. The thermal properties of the obtained Mn3O4 thin films were evaluated with a newly developed in situ emission FTIR method. The performance of Mn3O4 grown on flexible stainless steel mesh substrates was investigated toward the oxidation of CO and C3H6. X-ray diffraction (XRD) patterns, FTIR, and Raman spectroscopy reveal that only the single-phase tetragonal Mn3O4 spinel structure was obtained within the temperature range of 350–500 °C. The as-deposited Mn3O4 is thermally stable up to 800 °C, and its reduction plays a determinant role in the catalytic process. Compared to conventional powder catalysts, the combination of PSE-CVD, in situ emission FTIR, and the flexible substrate provides a novel tool for catalyst synthesis and the evaluation of the thermal properties and catalytic performance.

Structure sensitivity of propene oxidation over Co-Mn spinels

Single-phase cobalt–manganese spinel oxides (Co3−nMnnO4, CMO) were studied for the catalytic oxidation of propene in a systematic optimization strategy. CMO films were synthesized by pulsed-spray evaporation chemical vapor deposition (PSE–CVD) and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman and Ultraviolet–Visible (UV–Vis) spectroscopy. The effect of Co/Mn ratio in the mixed oxide systems on their catalytic activity was investigated in a fixed-bed reactor at T=100–800°C, with a space velocity of 90,000mL/gcath and a feed of 2% C3H6/20% O2/78% Ar. XRD patterns, FTIR and Raman spectroscopy reveal that a cubic single-phase spinel structure is obtained for n⩽1.23, while a tetragonal spinel structure is observed for n>1.23. With increasing of the manganese content, the temperature–programmed analysis demonstrates a lower reducibility, a general decrease of the temperature required for the reduced samples to be re-oxidized and increasing thermal stability. The catalytic tests show that the involvement of cobalt–manganese oxides in propene oxidation suppresses the formation of reaction intermediates, favoring the selectivity toward CO2 at low temperatures. Co2.35Mn0.65O4 exhibits the best catalytic performance, which follows in line with its better reducibility compared with the other compositions in the series of CMO oxides. These results show the great potential of CMO for future industrial application as a low-temperature catalytic system which does not rely on precious metals.

Catalytic oxidation of VOCs over mixed Co–Mn oxides

This work reports the synthesis and characterization of single-phase cobalt manganese oxide (CMO) spinels Co3−xMnxO4 (0≤x≤0.34) prepared by the pulsed-spray evaporation chemical vapor deposition (PSE–CVD) method. Structure and cationic distribution of the obtained films were characterized by XRD, FTIR, XPS and Raman spectroscopy. Temperature-programmed reduction/re-oxidation (TPR/TPO) was used to elucidate the redox properties of the deposited films. The electrical resistivity was measured in the temperature range of 27–450°C. XRD, FTIR and Raman spectra reveal the formation of single-phase cubic spinel structures up to x=0.34. With the substitution of cobalt cations with Mn3+ and Mn4+ ions, the unit cell of the cubic spinel shows a linear increase; the TPR results indicate a lower reducibility while the TPO results display no evident change; also, the ratio Co3+/Co2+ decreased and both electrical resistivity and thermal stability showed increasing trends. The observed behavior is attributed to the progressive incorporation of manganese, which induces structural defects favoring the formation of anionic vacancies and the restriction of the oxygen mobility. The catalytic activities of the doped spinels were investigated for the deep oxidation of unsaturated hydrocarbons (C2H2 and C3H6). The introduction of a slight amount of manganese shifted the light-off curves toward lower temperatures. Based on the XPS results, the enhanced catalytic activity is thought to benefit from the abundant presence of oxygen vacancies in the doped oxide.