MCM41 and silica supported MoVTe mixed oxide catalysts for direct oxidation of propane to acrolein

摘要

Bulk Mo_(1.3)V_(0.3)Te_(0.3) mixed oxide and MCM41 and amorphous silica supported Mo_(1.3)V_(0.3)Te_(0.3) mixed oxide (3 and 8 mol%,i.e.6 and 15% monolayer coverage on MCM41 and 19 and 51 % monolayer coverage on silica,respectively) catalysts have been synthesized and studied for direct oxidation of propane (DOP) to acrolein (ACR).After calcination at 853 K for 2 h under flowing nitrogen,characterization results (XRD,Raman and TEM-EDX) show that Mo species,MoV,MoTe and VTe mixed oxides with various compositions are present in the samples before and after testing,but after testing the EDX analyses indicate more domains rich in Mo when using a narrow electron beam (phi approx 5-10 nm in size),particularly for bulk and 8 mol% supported samples.At variance,broad electron beam (phi approx 50-100 nm in size) EDX analyses give values close to chemical compositions.This shows that under catalytic conditions,solid-state reaction has occurred leading to restructuring of several phases present in the samples,with extraction of some volatile MoO_3.Catalytic study at reaction temperature 773 K shows that amorphous silica and MCM41 supports exhibit catalytic activity in DOP to ACR,respectively.This means that homogeneous reaction occurs in the gas phase under the studied conditions after initiation on the solid surface.Mo_(1.3)V_(0.3)Te_(0.3) mixed oxide is shown to be highly dispersed on MCM41 and silica supports,particularly for low mixed oxide content (3 mol%) leading to higher selectivity and yield in ACR obtained than that for bulk samples,in particular for MCM41 support.This is indicated to arise from a better dispersion of the active phases,which favors redox properties of the catalytic materials and prevents deep oxidation of propane.