Morphology-dependent Catalytic Activity Research Articles

Effect of deposition temperature on topography and electrochemical water oxidation of NiO thin films

The deposition temperature plays a significant role in controlling the crystallinity, morphology, and texture of thin films. Herein, we report the fabrication of nickel oxide thin films on a fluorine-doped tin oxide-coated glass substrate via a single-step aerosol-assisted chemical vapor deposition technique. Variable temperatures from 450 to 525 °C were used for the fabrication of these NiO thin films. The crystalline structure of nickel oxide thin films was determined by X-ray diffraction which showed cubic structure having space group Fm3m, and unit cell lattice parameters of a = b = c = 4.17 Å that crystallize preferentially along (200) plane. While the Raman spectroscopic study revealed the presence of peaks corresponding to nickel oxide structure. The surface chemical composition and oxidation states were investigated by X-ray photoelectron spectroscopy. Moreover, field-emission scanning electron microscopy aided in examining the temperature-dependent topography and microstructure of films. It was observed that when deposition temperature is increased from 450 to 525 °C, the bandgap energy decreased from 3.59 to 3.41 eV. The electrocatalytic activity for the oxygen evolution reaction was performed under alkaline conditions, using linear sweep voltammetry and cyclic voltammetry at different scan rates. Moreover, ohmic drop and charge transfer resistance are estimated by electrochemical impedance spectroscopy. The nickel oxide deposited at 500 °C showed the highest current density and the earliest onset overpotential as compared with other samples at different temperatures. Morphology-dependent catalytic activity is attributed to substrate temperature which significantly affects the growth of nickel oxide. Cyclic voltammetry reveals the Ni redox feature due to the active phase of nickel (oxy)hydroxide (NiOOH) and there was no significant current until 1.5 VRHE. Measurements of activity as a function of substrate temperature were consistent with the hypothesis that different morphology of the electrode exerts different charge transfer activation on nickel oxide. These results suggested that electrocatalysts coupled with controlled morphology can be tuned in terms of high performance, commercial applicability, and water-splitting devices.

Solvent-Directed Morphological Transformation in Covalent Organic Polymers

Synthesis of bi-functional covalent organic polymers in two distinctive morphologies has been accomplished by simply switching the solvent from DMF to DMSO when 1,3,5-tribenzenecarboxyldehyde and 2,5-diaminobenzene sulfonic acid were reacted via Schiff base condensation reaction to afford covalent organic polymers (COPs) encompassing flower (F-COPDMF)- and circular (C-COPDMSO)-type morphologies. Chemical and morphological natures of the synthesized COPs were compared by characterization using TEM, SEM, XRD, FT-IR, and XPS analysis techniques. Besides diverse morphology, both the polymeric materials were found to comprise similar chemical natures bearing protonic acid–SO3H and Lewis base–C=N functionalities. Subsequently, both the COPs were evaluated for the synthesis of hydroxymethylfurfural (HMF) by the dehydration of fructose to investigate their morphology-dependent catalytic activity.

Morphology-dependent catalytic activity of Fe2O3 and its graphene-based nanocomposites on the thermal decomposition of AP

The spherical, hollow and tubular Fe2O3 (s, h and t) and their graphene-based nanocomposites rGO-Fe2O3 (s, h and t) were fabricated using the facile solvothermal methods. The morphologies and compositions of the as-synthesized Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites were systematically characterized by SEM, TEM, XRD, FTIR and XPS methods. Then, the effect of the catalytic performance of Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites on the thermal decomposition of ammonium perchlorate (AP) were studied by DSC method. The DSC results showed that all of the Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites can effectively promote the thermal decomposition of AP. Besides, rGO-Fe2O3(s) nanocomposite has the best catalytic performance, and the high-temperature decomposition exothermic peak of AP was significantly reduced after its mixing with rGO-Fe2O3 (s) nanocomposite. It can be seen that the effects of Fe2O3 on AP decomposition is mainly reflected in the high temperature process, while the effects of rGO-Fe2O3 (s) on AP decomposition is reflected in both high and low temperature stages, and the effect on the high temperature stage is more significant. The excellent catalytic performance of rGO-Fe2O3 (s) nanocomposite can be attributed to the in-situ growth of Fe2O3 on the surface of rGO, which contributes to the low temperature decomposition process of AP.

Support morphology-dependent catalytic activity of the Co/CeO2 catalyst for the aqueous-phase hydrogenation of phenol

The less hydrophilic Co/r-CeO2 catalyst inhibits the adsorption of water and further promotes the adsorption and activation of phenol.

Morphology Controlled CuO Nanostructures for Efficient Catalytic Reduction of 4-Nitrophenol

Catalytic transformation of nitroaromatic compounds in wastewater using nanostructured catalysts is a promising method for wastewater treatment. Here, we report a systematic study on morphology-dependent catalytic activity of CuO nanostructures for efficient reduction of 4-nitrophenol (4-NP) in water. The morphology of CuO nanostructures was controllably varied from nanorods, nanosheets and hierarchical 3D flower-like structures by simply varying ammonia concentration in a simple wet chemical approach. Catalytic transformation of toxic 4-NP into useful 4-aminophenol by the prepared nanostructured CuO samples were investigated. The impact of morphology on the catalytic activity of nanostructured CuO catalysts was examined. It was observed that hierarchical 3D flower-like CuO catalysts show enhanced catalytic activity as compared to nanorods and nanosheets. The origin of this morphology-dependent catalytic activity of CuO nanostructures is discussed.

Morphology-Dependent Catalytic Activity of Ru/CeO₂ in Dry Reforming of Methane.

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.

Effect of the morphology on the vapor phase benzene catalytic hydrogenation over Pd/CeO2 catalyst

CeO2 nanorods and nanocubes, which were used as supports to Pd (3.0 wt.%)/CeO2 catalysts, which were prepared by hydrothermal method. TEM, HRTEM, XRD, and H2-TPD were used to study the physic-chemical properties of the Pd/CeO2 catalysts. The Pd/CeO2 catalysts were applied to investigate the vapor phase benzene catalytic hydrogenation reaction under atmospheric pressure at the temperature of 100–200 °C. Results show that the Pd/CeO2 catalysts exhibit morphology-dependent catalytic activity. The Pd/CeO2 nanorod catalyst (PC100) has a superior vapor phase benzene catalytic hydrogenation performance. The benzene catalytic hydrogenation conversion and cyclohexane selectivity are 96.4% and 100% at 200 °C, respectively.

Morphology-dependent catalytic activity of plasmonic MoO3−x for hydrolytic dehydrogenation of ammonia borane

Series of plasmonic MoO[Formula: see text] particles have been prepared by a facile solvothermal method to produce hydrogen via hydrolytic dehydrogenation of ammonia borane. Interestingly, the as-prepared MoO[Formula: see text] particles present various morphologies, i.e. flower, schistose and nanorod by simply tuning the reaction temperature and solvent volume ratio of distilled water and acetic acid. More importantly, these MoO[Formula: see text] particles with different morphologies exhibit various catalytic performances of NH3BH3 under the irradiation of visible light. Particularly, the flower-like MoO[Formula: see text] microstructure possesses the best catalytic activity for hydrogen production probably owing to the relatively large surface area and strong LSPR in the visible region.

Heterogeneous catalysis with a coordination modulation synthesized MOF: morphology-dependent catalytic activity

We report control over morphology of a micro-porous three-fold interpenetration amide-functionalized Zn(ii)-based MOF, [Zn2(oba)2(bpta)]·(DMF)3, TMU-22, for Knoevenagel condensation through coordination modulation growth.

First-principles investigation of the dissociation and coupling of methane on small copper clusters: Interplay of collision dynamics and geometric and electronic effects.

Small metal clusters exhibit unique size and morphology dependent catalytic activity. The search for alternate minimum energy pathways and catalysts to transform methane to more useful chemicals and carbon nanomaterials led us to investigate collision induced dissociation of methane on small Cu clusters. We report here for the first time, the free energy barriers for the collision induced activation, dissociation, and coupling of methane on small Cu clusters (Cun where n = 2-12) using ab initio molecular dynamics and metadynamics simulations. The collision induced activation of the stretching and bending vibrations of methane significantly reduces the free energy barrier for its dissociation. Increase in the cluster size reduces the barrier for dissociation of methane due to the corresponding increase in delocalisation of electron density within the cluster, as demonstrated using the electron localisation function topology analysis. This enables higher probability of favourable alignment of the C-H stretching vibration of methane towards regions of high electron density within the cluster and makes higher number of sites available for the chemisorption of CH3 and H upon dissociation. These characteristics contribute in lowering the barrier for dissociation of methane. Distortion and reorganisation of cluster geometry due to high temperature collision dynamics disturb electron delocalisation within them and increase the barrier for dissociation. Coupling reactions of CHx (x = 1-3) species and recombination of H with CHx have free energy barriers significantly lower than complete dehydrogenation of methane to carbon. Thus, competition favours the former reactions at high hydrogen saturation on the clusters.

Self-Assembly of Novel Mesoporous Manganese Oxide Nanostructures and Their Application in Oxidative Decomposition of Formaldehyde

Monodisperse manganese oxide honeycomb and hollow nanospheres have been prepared facilely at room temperature by varying the molar ratio of KMnO4 and oleic acid. These new nanomaterials were characterized by XRD, SEM, EDS, TEM, and BET measurements. They had robust nanostructures and were stable even after ultrasonic treatment (40 kHz, 120 W) for 30 min. A plausible mechanism of the formation of manganese oxide nanostructures was proposed. The manganese oxide nanomaterials showed high catalytic activities for oxidative decomposition of formaldehyde at low temperatures. Complete conversion of formaldehyde to CO2 and H2O could be achieved, and harmful byproducts were not detected in effluent gases. The catalytic activity of manganese oxide hollow nanospheres was much higher than that of honeycomb nanospheres, although the surface area of the latter was nearly 2 times as high as that of the former. The mechanism of such morphology-dependent catalytic activity was discussed in detail. The catalytic activities of the obtained manganese oxide nanospheres were also significantly higher than those of previously reported manganese oxide octahedral molecular sieve (OMS-2) nanorods, MnOx powders, and alumina-supported manganese-palladium oxide catalysts. Potential applications and future research efforts were proposed.