Oxidative conversion of propane to acrylic acid and acetic acid over mixed oxide catalysts

The oxidative conversion of propane to acrylic acid and acetic acid over Mo? V? Sb? R? O (R?La, Ce, Nd and Sm) catalysts at different reaction conditions (viz. temperature, C₃H₈/O₂ ratio, H₂O/C₃H₈ ratio, space velocity, etc.) was investigated. The catalytic activity and selectivity of the Mo? V? Sb catalyst are strongly influenced by the addition of rare earth metals to the catalyst. The addition of water vapour to the feed of propane and oxygen enhances greatly the formation of oxygenated products, particularly acrylic acid and acetic acid. The ratio of selectivities of acrylic acid to acetic acid was found to depend on the rare earth metal used in the catalyst's preparation and the reaction conditions. High contact times, i.e. high degrees of propane conversion, are detrimental to the formation of acrylic acid but beneficial for acetic acid formation. Copyright © 2005 Society of Chemical Industry     

Thermodynamic analysis of the inequality of the cohesive energy density and internal pressure of polymers

With a simple thermodynamic analysis, we show that polymers do not satisfy the two major criteria that are required for establishing a unique relationship between cohesion energy density (CED) and internal pressure (IP). Since IP can take values independently of CED, we contend that the IP/CED ratio cannot be established a priori, as the ratio depends on the thermodynamic variables (temperature, pressure, etc.) and the system of interest. POLYM. ENG. SCI. 45:798–800, 2005. © 2005 Society of Plastics Engineers     

Comparison of the single-bubble-class and modified two-bubble-class models of bubble column reactors

Gas phase conversions and product selectivities predicted by the single-bubble-class and modified two-bubble-class models of bubble column reactors are compared for a multistep gas-liquid reaction involving series/parallel steps. A situation is considered where the first reaction step is fast and occurs in the interfacial region while the other reaction steps are slow and occur only in the liquid bulk. Equivalent hydrodynamic and transport parameters provide a common basis for the comparison. The differences in the gas phase conversions predicted by these models are insignificant. However, the two models predict very different values of selectivities for the intermediate products. This analysis enables us to judge the range of applicability of the single-bubble-class model in design and scale-up of bubble column reactors.     

Growth factor receptor tyrosine kinases acutely regulate neuronal sodium channels through the src signaling pathway

Growth factor receptor tyrosine kinase (RTK)-activated signaling pathways are well established regulators of neuronal growth and development, but whether these signals provide mechanisms for acute modulation of neuronal activity is just beginning to be addressed. We show in pheochromocytoma (PC12) cells that acute application of ligands for both endogenous RTKs [trkA, basic FGF (bFGF) receptor, and epidermal growth factor (EGF) receptor] and ectopically expressed platelet-derived growth factor (PDGF) receptors rapidly inhibits whole-cell sodium channel currents, coincident with a hyperpolarizing shift in the voltage dependence of inactivation. Sodium channel inhibition by trkA and PDGF receptors is mutually occlusive, suggestive of a common signal transduction mechanism. Furthermore, specific inhibitors for trkA and PDGF RTK activities abrogate sodium channel inhibition in response to NGF and PDGF, respectively, showing that the intrinsic RTK activity of these receptors is necessary for sodium channel inhibition. Use of PDGF receptor mutants deficient for specific signaling activities demonstrated that this inhibition is dependent on RTK interaction with Src but not with other RTK-associated signaling molecules. Inhibition was also compromised in cells expressing dominant-negative Ras. These results suggest a possible mechanism for acute physiological actions of RTKs, and they indicate regulatory functions for Ras and Src that may complement the roles of these signaling proteins in long-term neuronal regulation.     

Antimicrobial properties of uncapped silver nanoparticles synthesized by DC arc thermal plasma technique

We, herein, report the antimicrobial properties of uncapped silver nanoparticles for a Gram positive model organism, Bacillus subtilis. Uncapped silver nanoparticles have been prepared using less-explored DC arc thermal plasma technique by considering its large scale generation capability. It is observed that the resultant nanoparticles show size as well as optical property dependent antimicrobial effect.     

Field emission and photo-catalytic investigations on hierarchical nanostructures of copper doped CdS synthesized by kitchen-chemistry approach

We herein report an economical and facile technique for the synthesis of hierarchical nanostructures of Cu doped CdS nanostructures by microwave assisted solvothermal technique using a household microwave oven. We attempted to establish the effect of variation of solvents ratio on the morphological and optical properties of the obtained nanoscale structures. The field emission characteristics of the copper doped CdS nanoarchitecture have been studied and the turn on field is found to be 2.8 V/microm for an emission current density of approximately 0.1 microA/cm2. Emission current stability is determined at the preset current of approximately 1 microA and approximately 10 microA for the stable duration of approximately 4 hrs. The observed field emission results envisage the possibility of using the present emitter in the field emission sources. We believe that this is a unique report on the synthesis as well as field emission studies of copper doped CdS nanostructures. Photocatalytic dye degradation ability of the Cu doped CdS nanostructures is observed to be less than the undoped CdS counterparts.     

Cracking of n-heptane over Brønsted acid sites and Lewis acid Ga sites in ZSM-5 zeolite

A series of gallium-containing ZSM-5 zeolites prepared by wet impregnation, ion-exchange and chemical vapor deposition (CVD) methods are compared in the cracking of n-heptane. Impregnation results in the dispersion of some of the gallium oxide clusters into the zeolite pore network as charge-compensating Ga species after calcination. Reduction of impregnated Ga/HZSM-5 catalysts leads to complete transformation of the oxidic Ga precursors to charge-compensating Ga⁺ and GaH²⁺ species. A small amount of divalent GaH²⁺ species can be stabilized; however, with increasing Ga/Al ratio monovalent cations dominate. While a model Ga/HZSM-5 catalyst prepared by CVD of Ga(CH₃)₃ containing mainly charge-compensating Ga cations displays high selectivity to dehydrogenated products (olefins, toluene and coke), catalysts with a lower Ga/Al ratio display improved activity with a product mixture resulting from contributions of Ga sites (dehydrogenation, aromatization, olefin cracking) and of Brønsted acid sites (protolytic cracking, olefin cracking). The synergy between Ga dehydrogenation sites and Brønsted acid sites is proposed to improve the dehydrogenation rate: the high acidity of the zeolitic proton facilitates hydrogen recombination and concomitant removal of product olefin from the Ga active sites. Ion-exchanged Ga/HZSM-5 catalyst which combines a difficult to reduce gallium oxide phase and high Brønsted acidity has the highest activity with relatively weak coke formation.