No abstract

The Rh-1.5P catalyst exhibited the highest activity among the investigated catalysts. ► Rh2P was easily formed in catalysts with a higher P loading. ► Higher P loadings and higher reduction temperatures led to aggregation of Rh species. ► RhP2 exhibits lower catalytic activity than Rh2P. ► High HDS activity was caused by small Rh2P formation at lower reduction temperature.

Preparat ion o f no ble met al (NM) (Rh, Pd, Ru, Pt) phosphide species and t heir cat alyt ic act ivit ies for hydrodesulfur izat ion (HDS) of t hiophene w er e invest igat ed. Noble met al phosphides (NM X P Y) cat alyst s were prepared by reduct ion o f Padded NM (NM-P) support ed on silica (S iO 2) wit h hydrogen. Hydrogen co nsumpt io n peaks at around 350−700 °C, which wer e at t ribut ed t o t he for mat io n o f NM X P Y , were obser ved in t emper at ure-programmed reduct io n (TPR) spect ra of al l NM-P/S iO 2. Furt her more, X-ray diffr act ion (XRD) pat t erns o f NM-P/S iO 2 indicat e t hat NM X P Y (Rh 2 P, Pd 4. 8 P, Ru 2 P, Pt P 2) were for med by hydrogen reduct ion at high t emperat ure. The reduct ion t emperat ure st rongly affect ed HDS act ivit ies o f NM-P/S iO 2 cat alyst s. The NM-P/S iO 2 cat alyst s, ot her t han Pt , showed higher HDS act ivit ies t han NM/S iO 2 cat alyst s. The HDS act ivit y o f t he Rh-P/S iO 2 cat alyst was t he highest amo ng t hose o f NM-P/S iO 2 cat alyst s. This act ivit y was higher than that of the NiP catalyst and was t he same as t hat of pre-sulfided CoMoP/Al 2 O 3 cat alyst. Furt her more, t he Rh-P/S iO 2 cat alyst showed st able act ivit y even aft er react ion for 30 h. The XRD, t ransmiss io n elect ron microscopy (TEM), and energy disper sive X-ray spect roscopy (EDS) result s revealed t hat t he for mat io n o f sma ll Rh 2 P part icles and suit able P addit io n t o for m Rh 2 P caused t he high HDS act ivit y o f t he Rh-P cat alyst .

A two-stage catalytic degradation of polyethylene using amorphous silica−alumina and HZSM-5 zeolite catalysts in series has been developed for converting the polymer into high-quality gasoline-range fuels. Compared with the one-stage degradation over each catalyst, the two-stage method provides some advantages. They are an improved gasoline yield and a high octane number despite low aromatics content. Significant results were obtained when silica−alumina and HZSM-5 were used in a weight ratio of 9:1 as upper and lower catalysts, respectively, in a flow reactor. The reverse sequence of catalysts showed no advantage. It was suggested that large pores and moderate acidity of the silica−alumina loaded in the upper layer operated favorably to catalyze the degradation of polyethylene into liquid hydrocarbons. The resulting oils showed low quality, and they were transformed into high-quality gasoline on the strongly acidic sites of the HZSM-5 loaded in the lower layer at the expense of oil yield. Increases in concentration of isoparaffins and aromatics contributed to the upgrading.

For chemical recycling of waste plastics, HZSM-5, HY, and H-mordenite zeolites and silica−alumina were examined as catalysts for the degradation of polyethylene in a fixed-bed flow reactor system, and their activities and deactivation behaviors caused by coke deposition were studied. HZSM-5 catalyst was found to be very effective for the production of gasoline-range fuel oils mainly consisting of isoparaffins and aromatics and showed no deactivation due to a very low yield of coke deposited on the catalyst surface, whereas in the degradation of polystyrene a marked deactivation was observed (Uemichi et al. Kobunshi Ronbunshu 1993, 50, 887). Silica−alumina gradually deactivated as time on stream increased, but the degree of deactivation was less than expected from the deposition of a significant amount of coke, probably because the coke deposition in the large pores of the catalyst caused no marked influence on the diffusion of the decomposed fragments involved in the reaction. On the other hand, deactivations of HY and H-mordenite were striking; the latter was most abruptly deactivated, resulting in a marked decrease in the liquid yield. From the surface area measurements of the used catalysts, it was suggested that the pores of HY were sufficiently filled out with coke, while pore blocking by coke occurred in the unidimensional channels of H-mordenite.