Electron Spin Resonance and Electron Spin Echo Modulation Studies of Adsorbate Interactions with Cupric Ion on the Aluminum Content in Cu−AlMCM-41 Materials

Abstract

Employing electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopy, adsorbate interactions are studied in two types of ion-exchanged Cu−AlMCM-41 materials. One is structurally ordered Cu−AlMCM-41(60)-I, Cu−AlMCM-41(40)-I, Cu−AlMCM-41(20)-I, and the other is less structurally ordered Cu−AlMCM-41(15)-II. Four Cu(II) species are observed by ESR. Species A with ESR parameters g∥A = 2.406, A∥A = 0.0145 cm-1, and g⊥A = 2.081 is assigned to octahedral Cu(II) and is observed in hydrated Cu−AlMCM-41. Species B with g∥B = 2.317, A∥B = 0.0176 cm-1, and g⊥B = 2.076 is assigned to distorted octahedral Cu(II) and is observed in dehydrated samples. Species C with g∥C = 2.430, A∥C = 0.0125 cm-1, and g⊥C = 2.091 is also assigned to octahedral Cu(II) and is observed after adsorption of CH3OD. Species D contains square planar D1 Cu(II) with g∥D1 = 2.280, A∥D1 = 0.0168 cm-1, and g⊥D = 2.058, and distorted octahedral D2 Cu(II) with g∥D2 = 2.249 and A∥D2 = 0.0190 cm-1 after adsorption of ammonia. The...