Korean Chemical Engineering Research

HWAHAK KONGHAK,
Vol.32, No.2, 169-178, 1994

Cr³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ 이온이 지지된 zeolite의 6-R window상에서의 CO 흡착이론(I)

A Theoretical Adsorption Studies of CO on the Cr³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ Ion Exchanged 6-R Window of Zeolites(I)

김종현, 김영훈, 이종렬, 김종택

Faujasite와 A-형 제올라이트의 흡착 site인 6원환상에 Cr³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺등 전이금속이온이 교환될 때 그리고 이들 금속이온상에 CO 분자가 흡착되었을 때의 금속이온의 전하, CO분자와의 결합강도, 결합거리, CO 의 결합강도, 원자전하 등을 CNDO/2 방법에 의하여 6-Ring 모델을 써서 계산하였다. 계산 결과는 6원환에 지지된 상태에서 현장전하가 Cr³⁺는 +3.67, Fe²⁺는 +1.96, Fe³⁺는 3.33, Co²⁺는 +2.60, Ni²⁺는 +1.85, Cu²⁺는 +1.70의 값을 띠고 있었다. 전이금속이온들은 6원환에 지지되었을 때 산소로부터 전자를 받아 T(Si, Al)원자에게 주어 산소의(-) 전하와 T의(+)전하를 동시에 감소시키고 있었다. 그리고 골격 T-O의 결합강도를 증가시켰다. CO의 흡착은 CO→M로의 전자이동이 수반되었고, C-M의 결합차수는 Ni²⁺와Fe²⁺가 약 0.25로 큰 편이었고 CO²⁺가 0.006으로 가장 약했다. 그와 동시에 C-O의 결합차수는 Co²⁺, N²⁺, Fe²⁺의 영향으로 2.15정도로 가장 적었다. 그리고 계산에 의한 흡착 energy의 크기는 Co²⁺>Ni²⁺>Cu²⁺>Fe²⁺>Fe³⁺>Cr³⁺의 차례였다.

Located positions, charges, bond orders, potential energy variations and theoretical adsorption energies of CO on the Cr³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Cu²⁺ exchanged 6-membered ring window model were calculated by means of CNDO/2 method. Significant changes on the charges of cations and of skeletal atoms due to the cation exchanges were noticed; Charges of cation such as Cr³⁺, Fe³⁺ and Co²⁺ increased to +3.67, +3.33 and +2.60 respectively while those of the others decreased. Transition metal cations induced an electron transformation, ruled out by the lowering negative charges of oxygen as well as positive charges of Si and Al atoms in the 6-R. This eventually led to strengthen the bond orders of skeletal atoms. Adsorption of CO took place in due cause of electron donation from CO molecule to the skeletal atoms through the cations Co²⁺ manifested weakest bonding order with CO molecule. The heats of adsorption of CO on the 6-R model were calculated to be following orders : Co²⁺>Ni²⁺>Cu²⁺>Fe²⁺>Fe³⁺>Cr³⁺

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