291201 Propylene (C3=) Metathesis On MoOx/SBA-15 Catalysts: In Situ Characterization and Active Site Counting

Monday, October 29, 2012
Hall B (Convention Center )
Vuong Nguyen and Soe Lwin, Chemical Engineering, Lehigh University, Bethlehem, PA

Propylene (C3=)  Metathesis on MoOx/SBA-15 catalysts: in situ characterization and active site counting


Vuong Nguyen a, Soe Lwin a, Kazuhiko Amakawa b, Anitha  Patlolla c, Israel E. Wachs a, Robert Schlögl b, Annette Trunschke b , Anatoly I. Frenkel c


a Operando Molecular Spectroscopy and Catalysis Laboratory, Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA

b Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany

c Department of Physics, Yeshiva University, New York, NY 10016, USA

                Olefin metathesis is a very significant industrial reaction which finds applications in producing important petrochemicals, oleochemicals, polymers and specialty chemicals. Mesoporous silica-supported molybdenum oxide (MoOx/SBA-15)  catalysts are favorable over other heterogeneous catalytic systems (W, Re, etc) due to their high selectivity and intermediate operating temperatures.  In this project, the nature of catalytic active sites were studied in situ for the first time  using Raman, UV-Vis, XANES and IR spectroscopic techniques. In situ Raman showed that surface dioxo (O=)2MoO2 species are the dominant MoOx species for supported MoOx/SBA-15 catalysts. The crystalline MoO3 nanoparticles (NPs), which formed at the highest loading of 13.3%, were undesirable due to its strong Bronsted acidity which leads to more side products. In situ UV-Vis along with in situ Raman showed that MoO3 crystals were easiest to be reduced during the reaction, followed by surface dioxo (O=)2MoO2 and mono-oxo O=MoO4 species respectively in that order. In situ IR detected carbonyl (C=O) stretching band at 1650-1700 cm-1 region, implying the possibility of the pseudo- Wittig mechanism en route to the molybdenum carbene (Mo=CHR) species which were also detected. The selectivity of metathesis products (C2= and C4=) was highest for the sample with highest concentration of these surface species, even if the molybdenum concentration was not the highest, indicating that they are the selective catalytic active sites. The number of active sites was counted by the amount of formation of propene-1,1-d2 (CD2=CH-CH3) in the reaction of propene (CH2=CH-CH3)with ethylene-d4 (CD2=CD2 ) and found to be approximately 1.5% of total molybdenum atoms.


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