Cu(II)-adsorbate interactions in Cu(II)-exchanged K-L zeolite

The interaction of Cu(II) in Cu(II)-exchanged K-L channel-type zeolite with adsorbates containing coordinative nitrogen (ammonia, pyridine, hydrazine, and nitrogen monoxide) and carbon monoxide, benzene, and dimethyl sulfoxide was studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. Adsorption of ammonia produces a complex containing four mulecules of ammonia based on resolved nitrogen superhyperfine and analysis of deuterium modulation. Equilibrium with pyridine also results in a stable complex containing three molecules of pyridine based on resolved nitrogen superhyperfine. However, no resolved nitrogen superhyperfine between hydrazine and Cu(II) and nitrogen monoxide and Cu(II) is seen. Adsorption of nitrogen monoxide on hydrogen-reduced CuK-L samples produces an unstable Cu⁺-NO complex with reversed g value (g_⊥ > g_∥) ESR parameters and results in some reoxidation of reduced copper species back to cupric ions. Adsorption of carbon monoxide, benzene, or dimethyl sulfoxide causes changes in the ESR spectrum of Cu(II), indicating migration of Cu(II) into cation positions in the main channels where adsorbate coordination can occur. Cu(II) forms complexes with one molecule of benzene and dimethyl sulfoxide, respectively, based on ESEM data.