Effects of incorporated lead and chlorine on the oxidation of ethane on strontium hydroxyapatites

Facile Formation of the Partial Oxidation and Oxidative-Coupling Products from the Oxidation of Methane on Barium Hydroxyapatites with Tetrachloromethane

“…The atomic ratios of Ba/P and O/P in the near-surface region of the catalysts used were smaller than the expected values (1.67 and 4.00, respectively) for the stoichiometric chlorapatite, while those of Cl/P were greater than the expected value (0.33), and the Ba/P ratios were also smaller than those found by ICP (1.91−1.99), indicating significant differences between the compositions in the surface and bulk phases (Table ). The greater than expected Cl/P ratios may signal the formation of additional chlorinated species, such as the corresponding chloride observed in CaHAp and SrHAp, , and/or the existence of nonstructural chlorine in the surface. It is of interest to note that the composition of the near-surface region of BaHAp shows little or no dependence on the pressure of TCM (first three columns of Table ), suggesting that the surface may become saturated with chlorine, in whatever form, at the lowest partial pressure of TCM used in the present work.…”

Isomorphous Substitutions of Rare Earth Elements for Calcium in Synthetic Hydroxyapatites

“…21 Calcium hydroxyapatite and its derivatives are also used in gas sensors, 22,23 luminescent 24,25 and laser materials, 27,28 mercury tubes, 29 catalysts in organic reactions involving conversion of methane, dehydration of alcohol, hydrolysis of chlorobenzene, and others. [30][31][32][33][34][35][36][37][38][39][40][41][42][43] They can also be effectively used for nuclear waste disposal. 44 Hydroxyapatites modified by substitution of their constituents for atoms of other elements have better catalytic (Pb, Cu), [30][31][32][33][34] sensor (Na), 22 and antimicrobial properties (Ag) 35 than does pure hydroxyapatite.…”

“…For example, in luminescent and laser materials the concentration of dopant is about 1% and lower, 27 while in a strontium hydroxyapatite catalyst modified by lead, the concentration of Pb is 33%. 43 Substitutions also change interatomic distances in the structure and thereby affect adsorptive, catalytic, and sensor properties. According to Balandin's geometrical theory of catalysis, atomic arrangements on the contact surfaces in a case of chemosorption have to be in agreement with the geometry of adsorbed molecules of reactants.…”

“…phases. − They are also used as adsorbents in chromatography, including separation of proteins and nucleic acids, and also have application in the purification of human proteins . Calcium hydroxyapatite and its derivatives are also used in gas sensors, , luminescent , and laser materials, , mercury tubes, catalysts in organic reactions involving conversion of methane, dehydration of alcohol, hydrolysis of chlorobenzene, and others. − They can also be effectively used for nuclear waste disposal …”

Oxidative Coupling of Methane on Calcium-Lead and Barium-Lead Hydroxyapatites

“…3 It has been suggested that hydrogen-abstraction from methane to methyl radical proceeds on SrHAp, followed by the stabilization of the radical on PbHAp. 3,4 Since, on various catalysts consisting of alkaline earth metal cations, the activities for the oxidation of methane are strongly influenced by those divalent cations,' the effect of the introduction of PbHAp into calcium and barium hydroxyapatites (CaHAp:…”