从大木尺度现象看柳林香严寺毗卢殿建造年代之复杂性*

采用共沉淀法制备了高分散80%Ni/Al_2O_3催化剂,经350℃焙烧,得高分散NiO/Al_2O_3(NiO粒径～3 nm),将其以CS_2硫化(310℃, 4 h)或PPh_3磷化(320℃, 36 h),分别获得了高分散的硫化镍(Ni_3S_2和Ni_3S_4, 5.8 nm)和Ni_2P(7.0nm),在二苯并噻吩(DBT)的加氢脱硫(HDS)反应中, Ni_2P的活性远高于NiS_x(360℃时DBT的转化率分别为100%和75%).若将NiS_x用PPh_3磷化,则NiS_x全部转化为Ni_2P(13.3 nm),其HDS活性远高于原来的NiS_x且与直接磷化获得的Ni_2P(7.0 nm)相当.反之,若将Ni_2P用CS_2硫化,则Ni_2P物相不变,粒径也没有长大,表明Ni_2P物相远比NiS_x稳定,且其HDS活性高于直接磷化的Ni_2P,表明其Ni_2P表面可能生成了HDS活性更高的某种Ni-P-S物种.

Stability and Activity of Ni2P and NiSx for the Hydrotreating Reactions

A highly dispersed 80%Ni/Al2O3 catalyst was prepared by the co-precipitation method, which was calcined in air at 623 K to obtain a highly dispersed NiO/Al2O3 with NiO particles of about 3 nm. The NiO/Al2O3 was then sulfided with CS2 at 583 K to nickel sulfides (Ni3S2 and Ni3S4 of about 5.8 nm), or phosphided with PPh3 at 593 K to Ni2P (7.0 nm). The NiSx phases were completely converted into Ni2P (13.3 nm) when phosphided with PPh3 at 593 K, which was as active as the directly phosphided Ni2P (7.0 nm). In contrast, the phase and particle size of Ni2P did not change when treated with CS2 even at 633 K, indicating that the Ni2P was much more stable than the NiSx (Ni3S2 and Ni3S4). Moreover, the Ni2P/Al2O3 treated with CS2 at 583 K was more active than the directly phosphided Ni2P for the hydrodesulfication (HDS) reaction, indicating that the incorporation of S into Ni2P might generate some Ni-P-S species that were more active than the Ni-P surface species for the HDS reactions.