Study of Pd(I) adsorbate interactions in PdH-SAPO-5 molecular sieves by electron spin resonance and electron spin echo modulation

The locations and interactions of palladium ion in H-SAPO-5 molecular sieves with oxygen, water, benzene, ammonia, carbon dioxide, carbon monoxide, pyridine, and hydrazine have been studied by electron spin resonance (ESR) and electron spin echo modulation spectroscopies. Equilibration with benzene results in several new species due to benzene interaction with Pd(I). Adsorption of ammonia produces a complex containing two molecules of ammonia based upon resolved nitrogen superhyperfine. However, no resolved superhyperfine between pyridine and Pd(I) and hydrazine and Pd(I) is seen. The overall ESR spectrum of the complex between hydrazine and Pd(I) is similar to that of the ammonia-Pd(I) complex, which suggests that both nitrogens of one hydrazine molecule coordinate to Pd(I) to form a complex. Upon adsorption of carbon dioxide, only a weak interaction between carbon dioxide with Pd(I) is observed. However, adsorption of carbon monoxide results in a stable complex containing two molecules of carbon monoxide based upon resolved ¹³C superhyperfine. Adsorption of various molecules such as water, ammonia, pyridine, hydrazine, and even benzene and carbon monoxide leads to a change in the ESR spectrum which indicates the migration of Pd(I) ions to a position where the adsorbate can coordinate with them.