ELECTRON-SPIN-RESONANCE AND ELECTRON-SPIN ECHO MODULATION STUDIES OF CUPRIC ION LOCATION AND ADSORBATE INTERACTIONS IN THE CU2+-EXCHANGED H-SAPO-11 MOLECULAR-SIEVE

The locations and interactions of cupric ion exchanged into H-SAPO-11 molecular sieve with water, methanol, ethanol, ammonia, ethylene, and pyridine have been studied by electron spin resonance (ESR) and electron spin echo modulation spectroscopies. There is a gradual transition upon dehydration of CuH-SAPO-11 from a Cu2+ species with ESR parameters g(parallel-to) = 2.371 and A(parallel-to) = 159 x 10(-4) cm-1 to a Cu2+ species with g(parallel-to) = 2.302, g(perpendicular-to) = 2.071, A(parallel-to) = 185 x 10(-4) cm-1, and A(perpendicular-to) = 31 x 10(-4) cm-1. All of the samples with adsorbates show a major Cu2+ species with three different g values, which means that the Cu2+ ions lie in a distorted environment. Except for the ammonia-adsorbed sample, they show a weak reversed g value component in the ESR spectra with g(parallel-to) congruent-to 1.94, g(perpendicular-to) congruent-to 2.15, and A(parallel-to) congruent-to 106 x 10(4) cm-1. Equilibration with ethylene was slow compared to the cases of other adsorbates. Adsorption of ammonia produces a complex containing four molecules of ammonia based on resolved superhyperfine. However, no resolved superhyperfine between pyridine and Cu2+ is seen. Adsorption of polar molecules such as water, methanol, ethanol, ammonia, and pyridine leads to the migration of Cu2+ ions to a position where adsorbates can coordinate with the Cu2+ ions. In the hydrated sample, the Cu2+ ions directly coordinate to two water molecules. In the methanol-adsorbed sample, the Cu2+ ions directly coordinate to two methanols and indirectly coordinate to one methanol. In the ethanol-adsorbed sample, the Cu2+ ions directly coordinate to two ethanol molecules.