Synthesis of a resorcinol-based derivative as a corrosion inhibitor for low-carbon steel in 0.5 mol L-1 HCl medium: chemical, electrochemical, and theoretical aspects.

This work illustrated the synthesis of a new simple resorcinol derivative, 4,6-dimethoxyisophthalohydrazide (DMIH) and confirmed its structure using 1H-NMR spectroscopy. The inhibiting performance of the DMIH compound in resisting the pitting action of a 0.5 mol L-1 HCl solution on low-carbon steel (LCS) was assessed. The newly synthesized compound had a simple structure and was dissolved in acidic media. The efficiency of the inhibitor was examined using chemical and electrochemical methods. The DMIH compound significantly decreased the rate of dissolution of LCS in HCl solution by adsorption. The adsorption was based on the Langmuir model. The DMIH compound is adsorbed on LCS via both chemisorption and physisorption. The DMIH compound is a mixed-type inhibitor. An inhibition efficiency (IE) of 83.8% was obtained using 300 ppm of the DMIH compound at 298 K. The IE decreased to 72% as the temperature increased to 328 K. When the concentration of DMIH increased from 50 to 300 ppm, the charge transfer resistance (R ct) increased from 134.7 to 404.8 ohm cm2, and the capacitance of the adsorbed layer decreased from 38 × 10-6 to 11 × 10-6 F cm-2. The high IE of the synthesized inhibitor was validated by the quantum characteristics. Monte Carlo (MC) simulations revealed that the DMIH compound adsorbed to the LCS quite well. The presence of a protective film on the LCS specimen was verified by the scanning electron microscopy (SEM) and atomic force microscopy (AFM) results. DMIH has significant potential to function as a corrosion inhibitor, as indicated by the comparative study between its performance and that of previously reported compounds. Although the structure of the DMIH compound is simpler than that of other inhibitors, it has been proven to be more effective.

The electronic structure, surface properties, and in situ N2O decomposition of mechanochemically synthesised LaMnO3.

The use of mechanochemistry to prepare catalytic materials is of significant interest; it offers an environmentally beneficial, solvent-free, route and produces highly complex structures of mixed amorphous and crystalline phases. This study reports on the effect of milling atmosphere, either air or argon, on mechanochemically prepared LaMnO3 and the catalytic performance towards N2O decomposition (deN2O). In this work, high energy resolution fluorescence detection (HERFD), X-ray absorption near edge structure (XANES), X-ray emission, and X-ray photoelectron spectroscopy (XPS) have been used to probe the electronic structural properties of the mechanochemically prepared materials. Moreover, in situ studies using near ambient pressure (NAP)-XPS, to follow the materials during catalysis, and high pressure energy dispersive EXAFS studies, to mimic the preparation conditions, have also been performed. The studies show that there are clear differences between the air and argon milled samples, with the most pronounced changes observed using NAP-XPS. The XPS results find increased levels of active adsorbed oxygen species, linked to the presence of surface oxide vacancies, for the sample prepared in argon. Furthermore, the argon milled LaMnO3 shows improved catalytic activity towards deN2O at lower temperatures compared to the air milled and sol-gel synthesised LaMnO3. Assessing this improved catalytic behaviour during deN2O of argon milled LaMnO3 by in situ NAP-XPS suggests increased interaction of N2O at room temperature within the O 1s region. This study further demonstrates the complexity of mechanochemically prepared materials and through careful choice of characterisation methods how their properties can be understood.

Al-doped Fe2O3 as a support for molybdenum oxide methanol oxidation catalysts.

We have made high surface area catalysts for the selective oxidation of methanol to formaldehyde. This is done in two ways - (i) by doping haematite with Al ions, to increase the surface area of the material, but which itself is unselective and (ii) by surface coating with Mo which induces high selectivity. Temperature programmed desorption (TPD) of methanol shows little difference in surface chemistry of the doped haematite from the undoped material, with the main products being CO2 and CO, but shifted to somewhat higher desorption temperature. However, when Mo is dosed onto the haematite surface, the chemistry changes completely to show mainly the selective product, formaldehyde, with no CO2 production, and this is little changed up to 10% Al loading. But at 15 wt% Al, the chemistry changes to indicate the presence of a strongly acidic function at the surface, with additional dimethyl ether and CO/CO2 production characteristic of the presence of alumina. Structurally, X-ray diffraction (XRD) shows little change over the range 0-20% Al doping, except for some small lattice contraction, while the surface area increases from around 20 to 100 m2 g-1. Using X-ray absorption spectroscopy (XAS) it is clear that, at 5% loading, the Al is incorporated into the Fe2O3 corundum lattice, which has the same structure as α-alumina. By 10% loading then it appears that the alumina starts to nano-crystallise within the haematite lattice into the γ form. At higher loadings, there is evidence of phase separation into separate Al-doped haematite and γ-alumina. If we add 1 monolayer equivalent of Mo to the surface there is already high selectivity to formaldehyde, but little change in structure, because that monolayer is isolated at the surface. However, when three monolayers equivalent of Mo is added, we then see aluminium molybdate type signatures in the XANES spectra at 5% Al loading and above. These appear to be in a sub-surface layer with Fe molybdate, which we interpret as due to Al substitution into ferric molybdate layers immediately beneath the topmost surface layer of molybdena. It seems like the separate γ-alumina phase is not covered by molybdena and is responsible for the appearance of the acid function products in the TPD.