Utilization of Greenhouse Gases for Syngas Production by Dry Reforming Process Using Reduced BaNiO3 Perovskite as a Catalyst

For the commercialization of syngas production, the utilization of greenhouse gases and the fabrication of an active catalyst for the dry reforming methane (DRM) process are the biggest challenges because of deactivation by carbon deposition, oxidation, sintering, and loss of active surface sites under high temperature. In the present article, BaNiO3 perovskite was synthesized by the coprecipitation method, and its reduced form (r-BNO) was utilized for syngas production by the DRM reaction. It was found that the r-BNO showed high stability and good resistance against carbon deposition, however, the conversions (CH4 and CO2) have been found to be less than 50%. Many techniques such as TGA, XRD, FT-IR, UV-Vis, BET, SEM, TEM, XPS, TPR, TPO, and TPD were used in order to investigate the physical properties and evaluation conditions for syngas production. From the obtained results, it was revealed that BaNiO3 perovskite possessed a hexagonal crystal structure and perforated–rough surface; in addition, its structure was virtually regenerated by oxidation of the r-BNO catalyst, which provides a convenient way to regenerate the original catalyst in an oxidative atmosphere. Structural and surface alterations of the used catalyst, after the DRM reaction, were characterized by using TGA, TPO, and TEM, and it was found that there was no significant deposition of inert carbons (D and G) and deactivation of the r-BNO catalyst.

Modified Catalysts and Their Fractal Properties

Obtaining high-area catalysts is in demand in heterogeneous catalysis as it influences the ratio between the number of active surface sites and the number of total surface sites of the catalysts. From this point of view, fractal theory seems to be a suitable instrument to characterize catalysts’ surfaces. Moreover, catalysts with higher fractal dimensions will perform better in catalytic reactions. Modifying catalysts to increase their fractal dimension is a constant concern in heterogeneous catalysis. In this paper, scientific results related to oxide catalysts, such as lanthanum cobaltites and ferrites with perovskite structure, and nanoparticle catalysts (such as Pt, Rh, Pt-Cu, etc.) will be reviewed, emphasizing their fractal properties and the influence of their modification on both fractal and catalytic properties. Some of the methods used to compute the fractal dimension of the catalysts (micrograph fractal analysis and the adsorption isotherm method) and the computed fractal dimensions will be presented and discussed.

Importance of Surface Topography in Both Biological Activity and Catalysis of Nanomaterials: Can Catalysis by Design Guide Safe by Design?

It is acknowledged that the physicochemical properties of nanomaterials (NMs) have an impact on their toxicity and, eventually, their pathogenicity. These properties may include the NMs’ surface chemical composition, size, shape, surface charge, surface area, and surface coating with ligands (which can carry different functional groups as well as proteins). Nanotopography, defined as the specific surface features at the nanoscopic scale, is not widely acknowledged as an important physicochemical property. It is known that the size and shape of NMs determine their nanotopography which, in turn, determines their surface area and their active sites. Nanotopography may also influence the extent of dissolution of NMs and their ability to adsorb atoms and molecules such as proteins. Consequently, the surface atoms (due to their nanotopography) can influence the orientation of proteins as well as their denaturation. However, although it is of great importance, the role of surface topography (nanotopography) in nanotoxicity is not much considered. Many of the issues that relate to nanotopography have much in common with the fundamental principles underlying classic catalysis. Although these were developed over many decades, there have been recent important and remarkable improvements in the development and study of catalysts. These have been brought about by new techniques that have allowed for study at the nanoscopic scale. Furthermore, the issue of quantum confinement by nanosized particles is now seen as an important issue in studying nanoparticles (NPs). In catalysis, the manipulation of a surface to create active surface sites that enhance interactions with external molecules and atoms has much in common with the interaction of NP surfaces with proteins, viruses, and bacteria with the same active surface sites of NMs. By reviewing the role that surface nanotopography plays in defining many of the NMs’ surface properties, it reveals the need for its consideration as an important physicochemical property in descriptive and predictive toxicology. Through the manipulation of surface topography, and by using principles developed in catalysis, it may also be possible to make safe-by-design NMs with a reduction of the surface properties which contribute to their toxicity.

Development of hollow δ-FeOOH structures for mercury removal from water

δ-FeOOH, a magnetic iron oxyhydroxide, has a significant number of -OH groups on its surface. These provide an attractive platform for heavy metal species in contaminated water, giving it potential as an adsorbent. Its performance can be improved by increasing the number of active surface sites. δ-FeOOH hollow structures were synthesized on a mesoporous silica surface then treated with NaOH solution. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that structure synthesis was successful. δ-FeOOH, 5,27 nm, hollow crystals were produced with 63 m2 g−1 surface area and 20 nm average pore size. The point of zero charge was 4.72, which is beneficial for Hg(II) adsorption near neutral pH. The maximum Hg(II) adsorption capacity at pH 7 was determined as 89.1 mg g−1. The kinetics data were best fitted by a pseudo-second-order model with k2 equal 0,1151 g mg−1min−1. Finally, a nanomaterial filter was developed and used to remove mercury in water samples from a Brazilian river.

Highly Efficient Adsorption of Cd(II) onto Carboxylated Camelthorn Biomass: Applicability of Three-Parameter Isotherm Models, Kinetics, and Mechanism

A series of malonic acid treated camelthorn (MATC) sorbents were produced via the reaction of camelthorn biomass with malonic acid, and factors affecting the extent of modification were investigated, including malonic acid concentration, dehydration time and temperature. The optimum sorbent, by carboxylic acid content, was subsequently characterised for surface charge behaviour (pHPZC), surface chemical functionalities (FTIR), morphological structure (SEM), and available surface area. The sorbent was subsequently utilised for adsorption of Cd(II) ions from aqueous media, and parameters influencing adsorption at 30 °C, such as sorbent dose, initial solution pH, exposure time, metal concentration, were investigated. Isothermal analyses were performed using eight models, including two and three parameter equations, with appropriateness of fit assessed via non-linear regression analysis. The adsorption data indicated that the Langmuir model gives the most appropriate fit to experimental curves, with the models ordered as Langmuir > Hill > Toth > Sips > Jossens > Khan > Redlich-Peterson > Freundlich. The highest uptake (qmax) of 582.6 mg g−1 was determined at pH 6. The Freundlich constants, KF and n, at 30 °C were found to be 24.94 mg g−1 and 2.33, respectively. The value of n (2.33), being in the range 0–10, indicates that adsorption of Cd(II) ions onto malonic acid treated camelthorn biomass is favourable. Evaluation of a series of kinetic models, allowed elucidation of the adsorption mechanism, as a pseudo-second order model gave the most appropriate fit, indicating that chemisorption processes are involved. Cd(II) ions adsorption onto MATC is enhanced by a higher level of active surface sites but was show to be independent of surface area. The work presented here indicates that this sorbent offers effective adsorption potential for Cd(II) ions from water, with potential in wastewater processing.

Nanoscale oxidation behavior of carbon fibers revealed with in situ gas cell STEM

Thermal protection systems (TPS) are used to protect spacecraft payloads during the extreme conditions of atmospheric entry. The backbone of the composite TPS material used in the NASA Stardust Sample Return Capsule and the Mars 2020 mission is carbon fiber, which oxidizes at these temperatures and atmospheric conditions. This study presents the direct observation of carbon oxidation using in situ Scanning Transmission Electron Microscopy (STEM). A thin section of a commercially-available carbon fiber material containing multiple carbon structures was examined by STEM in a closed-environmental cell in which temperature was raised from 25 to 1050àC under a steady flow of air. Results show that the random polycrystalline carbon structure oxidized more uniformly and rapidly than the single crystallite region, which oxidized more anisotropically. These findings are the first to directly observe the structural dependence of carbon oxidation rates at these length-scales while also giving important insight into the onset of pitting at various active surface sites, important pieces in fundamentally understanding of carbon oxidation.

Interactions of ferro-nanoparticles (hematite and magnetite) with reservoir sandstone: implications for surface adsorption and interfacial tension reduction

There are a few studies on the use of ferro-nanofluids for enhanced oil recovery, despite their magnetic properties; hence, it is needed to study the adsorption of iron oxide (Fe2O3 and Fe3O4) nanoparticles (NPs) on rock surfaces. This is important as the colloidal transport of NPs through the reservoir is subject to particle adsorption on the rock surface. Molecular dynamics simulation was used to determine the interfacial energy (strength) and adsorption of Fe2O3 and Fe3O4 nanofluids infused in reservoir sandstones. Fourier transform infrared spectroscopy and X-ray photon spectroscopy (XPS) were used to monitor interaction of silicate species with Fe2O3 and Fe3O4. The spectral changes show the variation of dominating silicate anions in the solution. Also, the XPS peaks for Si, C and Fe at 190, 285 and 700 eV, respectively, are less distinct in the spectra of sandstone aged in the Fe3O4 nanofluid, suggesting the intense adsorption of the Fe3O4 with the crude oil. The measured IFT for brine/oil, Fe2O3/oil and Fe3O4/oil are 40, 36.17 and 31 mN/m, respectively. Fe3O4 infused with reservoir sandstone exhibits a higher silicate sorption capacity than Fe2O3, due to their larger number of active surface sites and saturation magnetization, which accounts for the effectiveness of Fe3O4 in reducing IFT.