(61c) Steam-Reforming of Methanol over Zn-Cr Catalysts in a Microreactor

Microreactors are expected to play a major role not only in process intensification but also in catalyst screening. The narrow radial distance enhances heat and mass transfer and thus offers an isothermal operation, which allows to measure intrinsic kinetic properties. The short contact time of reactants allows a quick response to dynamic changes in the inlet conditions and processes can be conducted more safely due to the characteristic dimensions lower than those of the conventional flame resistors. Apart from isothermal operation, rapid response and process security, further benefits in microreactors are fast and cost-saving screening of catalysts. A large number of catalysts can be valuated simultaneously.

Based on above advantages, a microreactor, made of stainless steel, was used to investigate steam-reforming of methanol on Zn-Cr catalysts. The reactor consisted of one chip and two flat stainless slabs. The plate (7.5cmx7.5cmx0.2cm) had 30 parallel rectangular channels and each channel was 1 mm wide, 1.2mm deep and 30mm long. Two flat slabs were used to cover the plate and to form isolated channels. The studies revealed the presence of a nearly uniform temperature, within 2°C, across the entire catalyst bed.

Zn-Cr catalysts with various calcined temperatures and Cr compositions (from 5 to 50%) were prepared by co-precipitation and impregnation methods. Their catalytic performances were investigated under different reaction conditions in the miroreactor and the catalysts calcined at 500°C showed high activity, selectivity and stability. To the catalysts prepared by co-precipitation method, adding Cr content greatly promoted the catalyst activity, but simultaneously increased CO formation significantly. To the catalysts prepared by impregnation method, increasing Cr resulted in declining catalyst activity. At higher Cr composition, the co-precipitation method was superior to the impregnation method. XRD characterization of freshly prepared catalysts confirmed the formation of spinel ZnCr2O4. The sizes of ZnO crystallites are believed to affect the catalytic performance.