Effect of Surface and Oxygen Coverage on Ethylene Epoxidation

Ozbek M. O., ÖNAL I., van Santen R. A.

TOPICS IN CATALYSIS, cilt.55, ss.710-717, 2012 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 55
  • Basım Tarihi: 2012
  • Doi Numarası: 10.1007/s11244-012-9870-7
  • Dergi Adı: TOPICS IN CATALYSIS
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Sayfa Sayıları: ss.710-717
  • Anahtar Kelimeler: Alkene, Epoxidation, Ethylene, Oxide, Silver, Gold, Copper, CATALYZED SELECTIVE OXIDATION, ADSORBED SPECIES PRESENT, ETHENE EPOXIDATION, SUBSURFACE OXYGEN, SILVER CATALYSTS, AG(111), OXIDE, MECHANISM, ADSORPTION, CHLORINE
  • Orta Doğu Teknik Üniversitesi Adresli: Evet

Özet

Ethylene epoxidation was studied as a function of oxygen coverage; for three different surfaces (111), (100) and (110) of three different IB metals using periodical DFT calculations. Oxygen coverage dependence was tested for 11, 25 and 33 % surface oxygen on Ag(111) surface. Calculations showed that increasing oxygen amount increased the exothermicity of the reaction while lowering the activation barriers. At studied oxygen ratios ethylene oxide and acetaldehyde formations proceed through OMC intermediate. In agreement with earlier studies, predicted selectivity is independent of surface structure. Generally the activation barriers for aldehyde formation are lower than those for epoxide formation on the studied surfaces. On copper surfaces the high stability of the precursor intermediates caused high activation barriers for the product formations. Also, epoxide formation is endothermic with respect to pre-oxygenated copper surfaces. On the other hand gold surfaces showed the smallest activation barriers for the product formations. Ag surfaces did not show conclusive differences for the activation barriers for epoxide versus aldehyde formation, which is in agreement with the 50 % EO selectivity of the un-promoted metallic silver.