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Selective Oxidative Dehydrogenation of Light Alkanes over Vanadate Catalysts
Published in Dale W. Blackburn, Catalysis of Organic Reactions, 2020
Mayfair C. Kung, Kimmai Thi Nguyen, Deepak Patel, Harold H. Kung
The formation of alkenes from alkanes involves the breaking of two C-H bonds. It is most likely that the breaking of the first C-H bond to form an alkyl species is the rate-limiting step. Indeed, this has been shown to be the case in the oxidation of butane on vanadyl pyrophosphate, as was shown by kinetic isotope studies.3 Whether this applies to the magnesium orthovanadate catalysts was studied by comparing the rates of reaction of various alkanes. The results are shown in Table 3.4 It can be seen that the rates of reaction decreased as 2-methylpropane > butane > propane > ethane. This trend can be understood if the rate reflects primarily the reaction involving the weakest C-H bond in the molecule. The bond energy of a primary, secondary, and tertiary C-H bond is 410, 395, and 375 kJ/mol, respectively.5 Thus 2-methylpropane, which has a tertiary carbon, reacts the fastest. Butane, which has two secondary carbon atoms, reacts faster than propane which has only one secondary carbon. Ethane, which has only primary carbon, reacts the slowest.
Shape Selective Catalysis
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
Most applications and manifestations of shape-selective catalysis involve acid-catalyzed reactions such as isomerization, cracking, dehydration, etc. Acid-catalyzed reactivities of primary, secondary, and tertiary carbon atoms differ. Tertiary carbon atoms form carbonium ions rather easily; therefore, they react much easier than secondary carbon atoms. Primary carbon atoms do not form carbonium ions under ordinary conditions and therefore do not react. Only secondary carbonium ions can form on normal paraffins; whereas, tertiary carbonium ions can generate on singly branched isoparaffins. Therefore, in most cases isoparaffins crack and isomerize much faster than normal paraffins. This order is reversed in most shape-selective acid catalysis; i.e., normal paraffins react faster than branched ones which sometimes do not react at all.
Engineering Aspects of Bioremediation
Published in Donald L. Wise, Debra J. Trantolo, Remediation of Hazardous Waste Contaminated Soils, 2018
Subrata Bandyopadhyay, Sanjoy K. Bhattacharya, Priyodarshi Majumdar
For effective implementation of in situ bioremediation, the following criteria must be met: The subsurface matrix must be permeable enough to allow perfusion with a solution of oxygen and nutrients.The concentration of substrate or pollutants (primary carbon source) should be higher than the minimum substrate concentration (Smin) for growth of microorganisms. A secondary carbon source needs to be added if the pollutant concentrations are too low to be utilized by microorganisms.Contaminant-degrading microorganisms must be present in the soil media.
Solvent Extraction and Complexation Studies of Pyridine-di-Phosphonates with Lanthanides(III) in Solutions
Published in Solvent Extraction and Ion Exchange, 2023
Ekaterina A. Konopkina, Petr I. Matveev, Anastasia V. Kharcheva, Tsagana B. Sumynova, Anton S. Pozdeev, Daniil A. Novichkov, Alexander L. Trigub, Paulina Kalle, Anna A. Kirsanova, Stepan N. Kalmykov, Vladimir G. Petrov, Nataliya E. Borisova
PyPOcHex extractant is the most effective among the studied ligands. This is explained, on the one hand, by the donor effect of the secondary carbon atom in the substituent and by the low preorganization energy due to the cyclic rigid substituent, as shown in the previous article.[29]