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

Abstract

In this work zeolites HY, HZSM-5 and mixes of zeolites with γ-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)–N2 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 °C, at 0.1 and 0.7 MPa with molar ratio of H2:n-C6H14 = 5.92 and n-hexane concentration 9.2 mol%. Mixing of γ-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 γ-Al2O3:HY = 2.5:1 and the optimal calcined temperature of NH4ZSM-5 to obtain HZSM-5 is 500–550 °C. An increase of reaction pressure from 0.1 to 0.7 MPa remarkably increased the activity, selectivity and stability of Pd-based catalysts.

n-Hexane hydro-isomerization over promoted Pd/HZSM-5 catalysts

“…(NH 4 )ZSM-5 zeolite (CBV3024E, SiO 2 /Al 2 O 3 = 30 was distributed by Zeolyst International, USA) was calcined at 500 °C for 3 h to obtain HZSM-5. 0.8 wt%Pd/HZSM-5 catalyst was prepared by impregnation method using the procedure described in our previous work [3]. Bi-metallic catalyst was synthesized by sequential impregnations: the first impregnation with an aqueous solution of the additive metal salt, Co(NO 3 ) 2 .6H 2 O (Merck), Ni(NO 3 ) 2 .6H 2 O (Merck), Fe (NO 3 ) 3 .9H 2 O (Merck), ReNO 3 .H 2 O (Aldrich), or Cu (NO 3 ) 2 .3H 2 O (Merck), followed by the second impregnation with palladium nitrate dihydrate to give 0.8 wt% Pd + 1.0 wt% of Co, Ni, Fe, Re, or Cu catalysts.…”

“…Although being very active and can be operated at moderate temperature, this type of catalyst requires complicated operation, causes corrosion, and being very sensitive to impurities like sulphur compounds and water [2]. In our previous studies [3,4], catalysts on the basis of Pt and Pd supported on HZSM-5 were developed and tested for n-hexane isomerization. The result indicated that 0.8%Pd/HZSM-5 catalyst exhibited comparable activity but less stable than 0.35%Pt/ HZSM-5 one.…”