Aromatic Hydrogenation Catalysis: A Review

High aromatic content in diesel fuel has been recognized both to lower the fuel quality and to contribute significantly to the formation of undesired emissions in exhaust gases [1, 2]. Because of the health hazards associated with these emissions, environmental regulations governing the composition of diesel fuels are being tightened in both Europe and the United States, leading to limitations on aromatics [3, 4].     

Multifunctional Nanochemistry: Ambient,Electroless, Template-Based Synthesis and Characterization of Segmented Bimetallic Pd/Au and Pd/Pt Nanowires as High-Performance Electrocatalysts and Nanomotors

Segmented noble-metal nanowires (NWs) represent an exciting, multifunctional, one-dimensional, structural architecture with a variety of potential applications. However, the widespread use of electrodeposition in the preparation of these systems has limited their potential to be produced on a large scale, since this protocol is costly and requires complex processes and caustic reaction media. Given the inherent limitations of electrodeposition, we report, for the first time, an ambient, surfactantless, template-based approach that is not only sustainable but also efficient for the reliable production of Pd/Pt and Pd/Au segmented NWs, possessing two spatially separated, chemically distinctive, but elementally pure, axial subunits. Our simple two-step synthetic approach allows for direct and predictable control over the relative segment lengths in these nanomaterials. Moreover, thorough structural characterization of these as-prepared samples confirms that our segmented NWs maintain high-quality, crystalline, elementally pure subunits with a well-defined interface between the constituent metals. In the context of preparing segmented NWs as multifunctional nanostructures, we demonstrate that these as-prepared NWs achieve high levels of performance when employed as both electrocatalysts and nanomotors.     

The usage of high metal feedstock for the determination of metal capacity of ARDS catalyst system by accelerated aging tests

For residue hydrotreating catalysts that are deactivated mainly by pore blockage due to deposition of metals, the capacity for accommodation of the deposited metals is an important parameter in determining its stability and life. The primary objective of the present work is to determine the maximum metal capacity of different catalysts that are used in different reactors of atmospheric residue desulfurization (ARDS) units by accelerated aging tests in a short duration. A feedstock with high metals content, namely, Boscan crude, was used for the tests in a multireactor pilot plant to cause complete deactivation of the catalysts by metal accumulation in a shorter period. The influence of operating temperature and LHSV on the rate of catalyst deactivation was also examined for the high metal feed. Catalyst deactivation rate was found to be more than five times faster for the high metal Boscan feed compared to the conventional atmospheric residue from Kuwait export crude. It was possible to determine MMOC of an ARDS catalyst system within 45–50 days by accelerated deactivation test using a high metal feed (e.g., Boscan crude).     

Environmentally friendly methodologies of nanostructure synthesis

Environmentally friendly synthetic methodologies have gradually been implemented as viable techniques in the synthesis of a range of nanostructures. In this work, we focus on the application of green-chemistry principles to the synthesis of complex metal oxide and fluoride nanostructures. In particular, we describe advances in the use of the molten-salt synthetic methods, hydrothermal protocols, and template-directed techniques as environmentally sound, socially responsible, and cost-effective methodologies that allow us to generate nanomaterials without the need to sacrifice sample quality, purity, and crystallinity, while allowing control over size, shape, and morphology.     

Water‐Dispersible,Multifunctional, Magnetic,Luminescent Silica‐Encapsulated Composite Nanotubes

A multifunctional one‐dimensional nanostructure incorporating both CdSe quantum dots (QDs) and Fe₃O₄ nanoparticles (NPs) within a SiO₂‐nanotube matrix is successfully synthesized based on the self‐assembly of preformed functional NPs, allowing for control over the size and amount of NPs contained within the composite nanostructures. This specific nanostructure is distinctive because both the favorable photoluminescent and magnetic properties of QD and NP building blocks are incorporated and retained within the final silica‐based composite, thus rendering it susceptible to both magnetic guidance and optical tracking. Moreover, the resulting hydrophilic nanocomposites are found to easily enter into the interiors of HeLa cells without damage, thereby highlighting their capability not only as fluorescent probes but also as possible drug‐delivery vehicles of interest in nanobiotechnology.     

SULFUR COMPOUND TYPE DISTRIBUTION IN NAPHTHA AND GAS OIL FRACTIONS OF KUWAITI CRUDE

ABSTRACT

The need for detailed information on the types of sulfur compounds present in various petroleum cuts has been well recognized by refiners and environmentalists worldwide. This need is growing in recent years in view of the current environmental regulations that limit the sulfur content of transportation fuels to very low levels. In the present work we have studied the distribution of different kinds of sulfur compounds present in light and middle distillates of Kuwait crude oil. A representative sample of Kuwait crude oil was fractionated into naphtha (15-160°C) and 10-15°C cuts in the gas oil boiling range (210-340°C) using an 80L capacity autodistillation unit “AUTODEST-800” according to ASTM 2892. The distribution of various types of sulfur compounds in each of these cuts was quantitatively estimated by capillary gas chromatography equipped with a sulfur chemiluminescence detector. Thiophene and its alkyl derivatives constituted about 60% of the total sulfur compounds in the naphtha fraction. The remaining 40% was composed of mercaptanes and alkyl sulfides. In the gas oil boiling range (210-340) two groups of sulfur compounds, namely, alkyl benzothiophenes and alkyl dibenzothiophenes were present. A major portion of the alkyl benzothiophenes was found in the fraction boiling in the narrow range 235-257°C. Among the alkyl dibenzothiophenes, the concentration of C, and C₂ DBTs decreased while that of higher alkyl DBTs (< C₃-DBTs) increased with increasing temperature. The C₁ and C₂ alkyl DBTs were highly concentrated in a fraction boiling between 280-325°C and these sulfur compounds were absent in the fraction boiling above 330°C. The industrial implications of these results are discussed.     

Functional Covalent Chemistry of Carbon Nanotube Surfaces

In this Progress Report, we update covalent chemical strategies commonly used for the focused functionalization of single‐walled carbon nanotube (SWNT) surfaces. In recent years, SWNTs have been treated as legitimate nanoscale chemical reagents. Hence, herein we seek to understand, from a structural and mechanistic perspective, the breadth and types of controlled covalent reactions SWNTs can undergo in solution phase, not only at ends and defect sites but also along sidewalls. We explore advances in the formation of nanotube derivatives that essentially maintain and even enhance their performance metrics after precise chemical modification. We especially highlight molecular insights (and corresponding correlation with properties) into the binding of functional moieties onto carbon nanotube surfaces. Controllable chemical functionalization suggests that the unique optical, electronic, and mechanical properties of SWNTs can be much more readily tuned than ever before, with key implications for the generation of truly functional nanoscale working devices.     

Modeling the crop transpiration using an optimality-based approach

Evapotranspiration constitutes more than 80% of the long-term water balance in Northern China. In this area, crop transpiration due to large areas of agriculture and irrigation is responsible for the majority of evapotranspiration. A model for crop transpiration is therefore essential for estimating the agricultural water consumption and understanding its feedback to the environment. However, most existing hydrological models usually calculate transpiration by relying on parameter calibration against local observations, and do not take into account crop feedback to the ambient environment. This study presents an optimality-based ecohydrology model that couples an ecological hypothesis, the photosynthetic process, stomatal movement, water balance, root water uptake and crop senescence, with the aim of predicting crop characteristics, CO₂ assimilation and water balance based only on given meteorological data. Field experiments were conducted in the Weishan Irrigation District of Northern China to evaluate performance of the model. Agreement between simulation and measurement was achieved for CO₂ assimilation, evapotranspiration and soil moisture content. The vegetation optimality was proven valid for crops and the model was applicable for both C ₃ and C ₄ plants. Due to the simple scheme of the optimality-based approach as well as its capability for modeling dynamic interactions between crops and the water cycle without prior vegetation information, this methodology is potentially useful to couple with the distributed hydrological model for application at the watershed scale.

     

Studies on rejuvenation of spent residue hydroprocessing catalysts by leaching of foulant metals: influence of inorganic salt additives on the leaching efficiency of organic acids

A comparative study has been made on the efficiency of oxalic, malonic and acetic acids for selective removal of metal foulants (e.g. vanadium) from spent residue hydrotreating catalysts in the presence and absence of aluminium nitrate. The influence of concentration of the added salt (aluminium nitrate) on the leaching efficiency of the three acids was also studied. The treated catalysts were characterized and the improvements in surface area, pore volume and HDS activity as a result of leaching with each reagent compared. The studies revealed that addition of aluminium nitrate enhanced the leaching efficiency of each acid to a different degree. The rate of vanadium leaching by oxalic acid was increased substantially by aluminium nitrate addition whereas for acetic acid there was only a moderate enhancement in leaching rate. The enhanced leaching by the aluminium nitrate-organic acid system may be explained in terms of a synergistic mechanism involving oxidizing and complexing reactions. The improvement in surface area and pore volume achieved on rejuvenation were related to the extent of removal of vanadium from the catalyst. The HDS activity of the catalyst was also increased significantly by leaching of the deposited metals. The selectivity for vanadium leaching (V/Mo ratio) was found to be an important factor for HDS activity recovery.