Studies On Mo(V)BiTeO/SiO₂ Catalysts For Selective Oxidation Of Propane To Acrolein

The selective oxidation of propane to acrolein is an important reaction for the utilizationof light alkanes and has been attracting a lot of attention in both academia and industry. Thisprocess, however, is usually accompanied by many difficulties resulting from the higherreactivity of acrolein than propane under the reaction conditions. A better understanding of theroles of the constituent elements and the relationship between the structure and performanceof catalyst is the key for the design of the active and selective catalysts.In the present work, a series of SiO₂ supported Mo oxide catalysts containing Bi and/orTe were prepared and studied for selective oxidation of propane to acrolein. In order to revealthe relationship of the catalytic performance with its physicochemical properties, the catalystswere characterized by XRD, Raman, in-situ Raman, XPS, H₂-TPR, NH₃-TPD and IRtechniques. Furthermore, the effect of V on the catalytic performance and structure ofMoBiTeO/SiO₂ catalyst were also investigated. The main results are summarized as follows:The addition of right amount Bi and Te to MoO/SiO₂ catalyst could greatly promote thecatalytic performance for selective oxidation of propane to acrolein. Under the optimizedreaction conditions (550℃, C₃H₈/O₂/N₂=1.2/1/4, 7200 mL·(g-cat)^-1·h^-1, 8 mm diameterreactor), MoBi_0.05Te_0.05/SiO₂ catalyst exhibited the best catalytic performance (Y_ACR.=12.3%).The characterization results indicated that there existed strong interaction between Mo oxideand Te oxide in MoBiTeO/SiO₂ catalyst. By the Mo-O-Te bond the formed Te-polymolybdatespecies improved the dispersion of Mo oxide active center. Besides, Te showed the ability ofα-H abstracting of propene and O-insertion to allyl. Bi component was supposed to dope inTe-polymolybdate species and some of Te⁴⁺ sites were replaced by Bi³⁺ cations, whichpromoted the mobility of lattice oxygen and catalytic performance.The active surface reconstruction was observed on MoBi_0.05Te₁/SiO₂ during propanepartial oxidation to acrolein after a period of reaction time at 570℃, correspondingly, bothpropane conversion and acrolein selectivity increased. The characterizations showed thatsome of tellurium was volatilized during reaction and such volatilization caused the activesurface reconstructed, namely part of Te-polymolybdate was destroyed and some of MoO₃formed. The synergy effect between Te-polymolybdate and MoO₃ might be the reason of theincreased catalytic performance. The study of the reference system (Te₂MoO₇ or TeMo₅O₁₆,MoO₃) indicated the synergy effect might due to MoO₃ facilitate the adsorption ofintermediate propene and the subsequent conversion to acrolein. Besides, MoO₃ also couldactivate propane.