Effect of carriers on physico-chemical properties and activity of Pd nano-catalyst in n-hexane isomerization

In this work zeolites HY, HZSM-5 and mixes of zeolites with gamma - Al2O3 in different ratios were taken as carriers for 0.8 wt% Pd catalysts. Physico-chemical characteristics of the catalysts were determined by methods of Brunauer-Emmett-Teller (BET)-N-2 adsorption, x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), hydrogen pulse chemisorption (HPC) and NH3 adsorption-desorption. The activity of catalysts was studied at 225-450 degrees C, at 0.1 and 0.7MPa with molar ratio of H-2:n-C6H14 = 5.92 and n-hexane concentration 9.2 mol%. Mixing of gamma-Al2O3 with zeolite made acidity of catalyst weaken and led to a decrease of Pd cluster size, to an increase of Pd dispersity and a reduction of the extent of Pd in the case of catalyst Pd/HY; but for the catalyst Pd/HZSM-5 such mixing led to the reverse effect. That is why the increase of activity in the first case and the decrease of activity in the second case have been observed. It has been found that the optimal ratio of mixed carrier is gamma-Al2O3: HY = 2.5: 1 and the optimal calcined temperature of NH(4)ZSM-5 to obtain HZSM-5 is 500-550 degrees C. An increase of reaction pressure from 0.1 to 0.7MPa remarkably increased the activity, selectivity and stability of Pd-based catalysts.