Insights into a Multifunctional Hybrid Catalyst Composed of Co/SiO2 and Pd/Beta for Isoparaffin Production from Syngas

The direct production of gasoline-range isoparaffins from synthesis gas (CO + H 2, syngas) via the Fischer−Tropsch (FT) route was investigated over a hybrid catalyst composed of Co/SiO 2 and Pd/β under the conditions of P = 1.0 MPa, W / F = 7.9 g·h·mol -1 and reaction temperatures of 503−513 K. Results indicate that the contact state between the Co/SiO 2 and the Pd/β particles in the hybrid catalyst (powdery mixture and granular mixture) had a clear effect on both the activity toward CO hydrogenation and the product distribution. Interestingly, the granular hybrid catalyst showed much higher performance in the case of isoparaffin selectivity than the powdery hybrid catalyst at the initial stage of the reaction. Furthermore, irrespective of the reaction conditions applied, the powdery hybrid catalyst gave apparently lower CO conversion and obviously higher CH 4 selectivity than the granular hybrid catalyst. Irrespective of the catalyst used, the total selectivity of isoparaffins (I/C 4 +) noticeably decreased with TOS due to the increase of selectivity of normal paraffins, the decrease of selectivity of isoparaffins, and less cracking of long-chain FT hydrocarbons. In the case of the powdery hybrid catalyst, a synergistic effect of the FT reaction over Co/SiO 2 and the hydroconversion reaction over Pd/β was suggested from the reaction results. A mechanistic model based on the migration of hydrogen species at the interfaces of the different particles was developed, and the reaction results were extensively discussed based on the proposed model.