Electron spin resonance and electron spin echo modulation spectroscopic analysis of palladium(I)-adsorbate interactions in PdH-SAPO-11 molecular sieve

Palladium(II) exchanged into H-SAPO-11 molecular sieve can be activated to form some Pd(I) which shows strong interactions with oxygen, water, ammonia, carbon dioxide, carbon monoxide, hydrazine, benzene and ethylene. The complexes have been studied by electron spin resonance and electron spin echo modulation spectroscopies. Pd(I) reacts with water vapor or molecular oxygen to form Pd(II)-O₂^-, indicating decomposition of water Long-term (12h) equilibration of an activated sample with water vapor results in a new Pd(I) species directly coordinated to two water molecules. Adsorption of ammonia produces two new Pd(I) complexes containing one and four molecules of ammonia based upon resolved nitrogen superhyperfine coupling. Hydrazine forms two weak complexes with Pd(I), but no nitrogen superhyperfine coupling is seen. Exposure to benzene also results in two weak complexes with Pd(I). Adsorption of carbon monoxide results in a single complex containing two molecules of carbon monoxide based upon resolved ¹³C superhyperfine coupling. Exposure to ethylene leads to room temperature ethylene dimerization to produce a Pd(I) complex with butene. These Pd(I) adsorbate interactions form a basis for potential catalytic applications of PdH-SAPO-11 molecular sieves.