Preparation Of Nickel Phosphides By Hydrogen Plasma Reduction And Their Catalytic Performance In Hydrotreatment

Transition metal phosphide has excellent physical and chemical properties,as a new type of semiconductor material,it has been widely used in optical,magnetic,catalytic and other fields.It received much attention in hydrogenation catalysis for its high activity and stability,however,the preparation of transition metal phosphide catalyst usually need harsh conditions,which limited their application.Therefore,many efforts has been put in optimizing the synthetic conditions.In this work,hydrogen plasma reduction method?PR?was used to prepare the unsupported Ni₂P and supported nickel phosphide catalysts?Ni₂P/SiO₂?the synthetic parameters were systematically studied.;The hydrorefining performance of the prepared metal phosphide catalysts was investigated using benzothiophene?DBT?and quinoline as the model compounds.The structure of the prepared metal phosphide catalystswere characterized by means of XRD,N₂ physical adsorption,XPS?HRTEM,CO CO chemisorption,thermo-gravimetric analyzer,TPR and ICP.A preliminary study was carried out on the catalytic hydrogenation reaction mechanism of the unsupported and supported transition metal phosphide catalyst prepared by PR method.With the diammonium phosphate and nickel nitrate as the precursor?Ni/P mole ratio=2?,through the calcination or none-calcination method,Ni₂P and Ni₂P/SiO₂ catalyst were prepared by hydrogen plasma?PR?as well as temperature programmed reduction?TPR?.The results showed that Ni₂O catalyst prepared by PR showed higher hydrodesulfurization activity than the Ni₂P catalyst prepared by TPR,this may due to the relatively low reduction temperature provided by PR method can improve the dispersion of the active species,thus improving the catalytic activity.The Ni₂O catalyst prepared by PR showed good stability,as shown in the continuous operation of 100 h HDS and 40 h HDN reaction,the catalyst shows rather stable activity,and the structure unchanged after the reaction.As for the Ni₂P/SiO₂ prepared by TPR,more Ni remains on the surface,which helped to improve the catalytic hydrogenation activity.With NaH₂PO₂ and NH₄H₂PO₂ as phosphide source respectively,both supported and unsupported Ni₂O catalyst were prepared successfully by PR method.The results showed that,with NaH₂PO₂ as the phosphide sourse,when Ni/P molar ratio of the precursor is 2,both unsupported Ni₂P and Ni₂P/SiO₂ can be synthesized by PR method.When NH₄H₂PO₂ as phosphide source,Ni₂P can not be synthesized in pure phase under similar condition.TGA analysis showed that under thermal treatment,NH₄H₂PO₂ are more easily to decompose and disproportionate,which may lead to a fast release of PH₃,thus unable to react further with Ni species to produce Ni₂P.Through the introduction of additives to the NH₄H₂PO₂ precursor?NaCl,KCl and P₂O₅?,can control the release of the volatile phosphide species during the thermal decomposition and disproportion of NH₄H₂PO₂,so that the pure Ni₂P can be successfully prepared.We further investigated the Ni₂P preparation condition by PR method,with Ni?OH?₂ and H₃PO₃ as raw material.The result showed that during the preparation of precursor,Ni?OH?₂ and H₃PO₃ can first react to form a stable Ni?PO₃?₂,which made the further preparation condition more difficult.Only under the large excess of P sourse?Ni/P=0.8?,pure Ni₂P can be successfully prepared in both supported and unsupported catalyst.