Characterization of zeolite supported mono- and bimetal clusters and their interaction with protons

The objectives of this research are to study the interaction of Pd with zeolitic protons and to characterize bimetal PdCu{dollar}sb{lcub}rm x{rcub}{dollar}, PdFe{dollar}sb{lcub}rm x{rcub}{dollar} and PtFe{dollar}sb{lcub}rm x{rcub}{dollar} clusters in Y zeolite.; Mass spectroscopy and FTIR were used to monitor the isotopic exchange of zeolitic protons with D{dollar}sb2{dollar}. Discrete groups of protons were differentiated from their exchange kinetics. Protons proximal to Pd particles were exchanged with D{dollar}sb2{dollar} as rapidly as H atoms adsorbed on Pd. For more remote protons the exchange rate was lower. Spillover of deuterium atoms from Pd particles over a longer distance was excluded because of the small exchange rate observed with a physical mixture of proton-free Pd/NaY and HY. Zeolitic protons enhanced metal dispersion by "chemically anchoring" small reduced Pd particles. These protons also reduced the propensity of very small Pd clusters to chemisorb hydrogen. The mononuclear Pd proton adduct (Pd-H{dollar}sb{lcub}rm x{rcub}rbracksp{lcub}rm x+{rcub}{dollar} did not catalyze D/H isotope exchange at 21{dollar}spcirc{dollar}C because of its inability to chemisorb H{dollar}sb2{dollar} or D{dollar}sb2{dollar}.; The presence of Pd and Pt enhanced the reducibility of Cu{dollar}sp{lcub}2+{rcub}{dollar} and Fe{dollar}sp{lcub}2+{rcub}{dollar} in Y-zeolites. The extent of Pd-enhanced reduction of Fe{dollar}sp{lcub}2+{rcub}{dollar} to Fe{dollar}spcirc{dollar} decreased with increasing proton concentration in the zeolite.; Bimetal PdCu particles in zeolite Y have been characterized using temperature programmed techniques in conjunction with EXAFS. It was shown that the protons generated from the reduction of Pd{dollar}sp{lcub}2+{rcub}{dollar} and Cu{dollar}sp{lcub}2+{rcub}{dollar} can selectively reoxidize Cu{dollar}spcirc{dollar} to Cu{dollar}sp+{dollar} and Cu{dollar}sp{lcub}2+{rcub}{dollar} at 210{dollar}spcirc{dollar}C and 500{dollar}spcirc{dollar}C, respectively. After complete "leaching" of Cu, the Pd particles were discerned from the alloy particles by their propensity to form hydrides.; The formation of PdFe{dollar}sb{lcub}rm x{rcub}{dollar} and PtFe{dollar}sb{lcub}rm x{rcub}{dollar} alloy clusters in NaY has been verified by TPR, TPD, FMR, FTIR, Mossbauer spectroscopy and CO hydrogenation studies. The extent of Fe reduction and reoxidation by zeolitic protons was quantified by TPR and TPD. An average composition of Pd{dollar}sb{lcub}16{rcub}{dollar}Fe{dollar}sb1{dollar}, Pt{dollar}sb{lcub}10{rcub}{dollar}Fe{dollar}sb1{dollar} and Pd{dollar}sb{lcub}10{rcub}{dollar}Fe{dollar}sb3{dollar} was found for the reduced clusters in PdFe/NaHY, PtFe/NaHY and neutralized PdFe/NaY, respectively. No {dollar}alpha{dollar}-Pd hydride is formed with PdFe{dollar}sb{lcub}rm x{rcub}{dollar} clusters under conditions where this hydride forms readily with Pd clusters. Strong ferromagnetic resonance signals owing to PdFe{dollar}sb{lcub}rm x{rcub}{dollar} or PtFe{dollar}sb{lcub}rm x{rcub}{dollar} particles suggested that Pd and Pt atoms surrounding an Fe atom became polarized. The presence of Fe significantly changed the activity and selectivity of NaY supported Pd and Pt catalysts in the conversion of CO + H{dollar}sb2{dollar}.