Novel approach to rhenium oxide catalysts for selective oxidation of methanol to DMM

In situ electrochemical redox tuning of Pd-Co hybrid electrocatalysts for high-performance methanol oxidation: Strong metal-support interaction

Construction of strong metal-support interaction (SMSI) is of fundamental interest in the preparation of supported metal nanoparticle catalysts with enhanced catalytic activity. Herein, we report a facile in situ electrochemical redox tuning approach to build strong interactions between metals and supports. As for a typical example, a composite electrocatalyst of Pd-Co hybrid nanoparticles directly developed on Ni substrate is found to follow a distinct surface self-reconstruction process in alkaline media via an in situ electrochemical redox procedure, which results in structural transition from the original nanoparticles (NPs) to nanosheets (NSs) coupled with a phase transformation of the Co component, Co → CoO/Co(OH)₂. The SMSI is observed in the electrochemically tuned Pd-Co hybrid system and leads to significantly enhanced catalytic activity for methanol oxidation reaction (MOR) due to the modified atomic/electronic structure, increased surface area, and more exposed electroactive sites. Compared with commercial Pd/C catalyst, the electrochemically tuned Pd-Co hybrid catalyst with SMSI exhibits superior catalytic activity (2330 mA∙mg_Pd^-1) and much better stability (remains 503 mA∙mg_Pd^-1 after 1000 cycles and 172 mA∙mg_Pd^-1 after 5000 s), and therefore has great potential in practical applications.

Thermal exfoliation of electrochemically synthesized graphite intercalation compound with perrhenic acid

In present work, we describe the synthesis of graphite intercalation compounds with perrhenic acid (HReO4-GIC) through the anodic oxidation of graphite in aqueous perrhenic acid solution and their thermal exfoliation. Due to electrochemical treatment of graphite in perrhenic acid solution, ReO4− ions are intercalated into interlayer spaces of graphite. Anodic oxidation of graphite in HReO4 solution leads to the formation of 3-stage GIC. Simultaneously, some amount of perrhenic acid becomes deposited on the graphite surface and edges. In the next step, thermal treatment of the previously synthesized GIC was performed, causing both the exfoliation of graphitic structure and transformation of perrhenic acid into rhenium oxides on the surface of graphene layers. The yielded product was exfoliated graphite-ReO2/ReO3 composite. The obtained composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. Additionally, specific surface area of the exfoliated materials was measured.

Self-passivating (Re,Al)B2 coatings synthesized by magnetron sputtering

(Re_0.67Al_0.10)B₂ and (Re_0.74Al_0.11)B₂ solid solution as well as Re_0.85B₂ thin films were deposited by hybrid RF-DC magnetron sputtering. X-ray diffraction (XRD) showed that all films exhibit the ReB₂ (P6₃/mmc) crystal structure. X-ray photoelectron spectroscopy (XPS) analyses performed on atmosphere exposed thin film surfaces suggest that ReB₂ corrodes, consistent with literature, by forming perrhenic acid (HReO₄) already after two days, while (Re_0.74Al_0.11)B₂ forms a self-passivating Al-oxide layer preventing corrosion in a time period ≥ 60 days. Hence, it is evident that Al additions to ReB₂ significantly increase the chemical stability during atmosphere exposure.

One-pot 1,1-dimethoxymethane synthesis from methanol: a promising pathway over bifunctional catalysts

Dimethoxymethane or DMM is a versatile chemical with applications in many industries such as paints, perfume, pharmacy, and fuel additives.

Application of modified CNTs with Ti(SO4)2 in selective oxidation of dimethyl ether

The possible reaction pathway of DME oxidation to DMM₂ over Ti(SO₄)₂/CNTs.

Reaction mechanism of methanol to formaldehyde over Fe- and FeO-modified graphene

We employed periodic DFT calculations (PBE-D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O-H cleavage. As a result, a methoxo-containing intermediate is formed. Subsequently, H-transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H2O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol(-1).

Platinum particles supported on mesoporous carbons: fabrication and electrocatalytic performance in methanol-tolerant oxygen-reduction reactions

In this report, we describe the preparation and electrochemical characterization of a Pt electrocatalyst, which was synthesized from hexachloroplatinic acid, using the incipient wetness impregnation method. This carbon mesoporous materials (Pt-CMMs) electrocatalyst was used for catalyzing the oxidation of methanol and its oxygen-reduction reaction. The electrocatalytic oxidation of methanol was studied using linear-sweep voltammograms (LSV), polarization and chronoamperometric measurements. Phase characterizations and morphological analyses were performed using 3D excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption measurements, and X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM) techniques; the ESEM system was equipped with an energy-dispersive spectrometer (EDS). The oxidation capacity measured using a LSV might explain the high activity exhibited by the Pt-CMM electrocatalysts in methanol-tolerant oxygen reduction, and the results demonstrated that the potential and current density of the main reaction peak of the Pt-CMMs electrocatalyst changed during the reaction. Moreover, EEFM spectroscopy and XRD were determined to be appropriate and effective methods for characterizing Pt clusters that enhance their intrinsic emission from Pt-CMMs electrocatalysts in electrocatalytic-treatment systems. Furthermore, the ESEM-EDS results showed that fresh Pt nanoparticles were highly dispersed on CMMs and featured a 20 nm diameter and a narrow particle-size distribution.