Reactions of ammonia with porous glass surfaces

Abstract

Infrared spectra of NH3 sorbed on highly dehydroxylated, deuterated, and fluoridated porous glass were recorded. Two pairs of bands at 3409 and 3320 cm-1 and at 3330 and 3308 cm-1 were attributed to physically adsorbed NH3, hydrogen bonded to the SiOH and BOH groups of the glass surface, respectively. Bands at 3368 and 3282 cm-1 were ascribed to a =B-NH3 complex. Two pairs of bands at 3569 and 3479 cm-1 and at 3543 and 3459 cm-1 were ascribed to =BNH2 and =SiNH2 groups, respectively. A single band at 3455 cm-1 was tentatively assigned to the N-H stretching vibration of a secondary amine, the nitrogen atom being bonded to two surface boron atoms.There have been numerous reports dealing with the sorption of NH3 on porous glass.1-15 A variety of experimental techniques has been used and there seems to be a general agreement about the role of surface silanol groups as sites for a weakly bonded NH3 adsorption. A strong adsorption requiring sites other than silanols has also been reported. Folman and Yates suggested that the strong sites were silicon or oxygen atoms.1 2345However, Cant and Little pointed out that porous glass contained 3% B203 and stated that it was not impossible that strongly bound NH3 was adsorbed on electron-deficient surface boron atoms themselves.12 Chapman and Hair similarly concluded that strong NH3 adsorption occurred on (1) D.

Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

“…We speculate that the N 2 formed in the blank reactions is generated by the reaction of t Bu 3 ArO . , with adsorbed NH 3 on the surface of the reaction vessels, as analogous blank reactions using TEMPO . (TEMPO .…”

“…We speculate that the N 2 formed in the blank reactions is generated by the reaction of t Bu 3 ArOC,with adsorbed NH 3 on the surface of the reaction vessels, [43] as analogous blank reactions using TEMPOC (TEMPOC = 2,2'-6,6'-tetramethylpiperidine-1-oxyl radical;B DFE of TEMPO-H = 65.2 kcal mol À1 in benzene) [13] with 14 NH 3 did not produce N 2 gas as determined by GC.I narigorous effort to eliminate the background N 2 formation, reactions were performed in quartz and Te flon flasks of identical size.H owever, all compositions tested yielded nearly the same amounts of N 2 (see Table S3;S I). Of the solvents screened for catalysis, t Bu 3 ArOC persists the longest in DME, which was chosen as asolvent for the catalytic trials.Catalytic turnover was determined by quantifying the liberated N 2 gas in the headspace of the flask by GC.I mportantly,control reactions were performed by reacting t Bu 3 ArOC with anhydrous 14 NH 3 in the absence of [Ru 15 NH 3 ] + .W ew ere surprised to detect aquantifiable amount (ca.…”

Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

“…3-5 10 À6 mol) of N 2 gas that was consistently produced in blank reactions with no Ru present. We speculate that the N 2 formed in the blank reactions is generated by the reaction of t Bu 3 ArOC,with adsorbed NH 3 on the surface of the reaction vessels, [43] as analogous blank reactions using TEMPOC (TEMPOC = 2,2'-6,6'-tetramethylpiperidine-1-oxyl radical;B DFE of TEMPO-H = 65.2 kcal mol À1 in benzene) [13] with 14 NH 3 did not produce N 2 gas as determined by GC.I narigorous effort to eliminate the background N 2 formation, reactions were performed in quartz and Te flon flasks of identical size.H owever, all compositions tested yielded nearly the same amounts of N 2 (see Table S3;S I). Consequently,t he N 2 quantified from blank reactions is subtracted from the total N 2 produced in the catalytic runs.Aturnover number (TON) (TON = mol N 2 mol À1 catalyst) is reported as the average of three catalytic runs after the blank subtraction.…”

Chemisorption sites on porous silica glass and on mixed-oxide catalysts

“…This band has been assigned (9,20) to a secondary amine group such as N o evidence of bands due to primary amine groups =B-NH, or =Si-NH, was found. Figure 2 shows the corresponding spectra for ammonia adsorbed on aerosil impregnated with zirconia.…”