Surface Polymeric Phosphate Ligand Modification Of Nickel Oxide Nanoparticles And Their Catalytic Applications

Surface ligand modification has emerged as an effective and elegant strategy to tune the catalytic reaction of metal nanoparticles(NPs).It can potentially alter the electronic and steric properties of the catalyst surface by modification to affect the adsorption property of substance,which is regarded as an important method to tune the catalytic activity,selectivity or stability of catalyst.To the best of our knowledge,there is no report about utilizing ligand modification to regulate the catalytic reaction of high-temperature(>300 ?)gas-phase reactions due to the volatility and limited thermal stability of traditional organic ligands.Thus in the field of nanocatalysis,it is of great importance to discover thermal-stable ligands and extend this effective modification strategy to more reaction system to tune the catalytic reaction.In this paper,we demonstrate polymeric phosphate(SPP)as an efficient and stable ligand which is successfully modified on the NiO NPs,and futher apply them in oxidative dehydrogenation of propane and methane combustion in which the reaction selectivity and sulfur tolerance are well-controlled,respectively.Polymeric phosphate as a thermal-stable ligand is introduced to surface ligand modification strategy to synthesis the nanocatalyst.Polymeric phosphate modified NiO is prepared by a post-treatment of NiO NPs in phosphate solution,followed by a high-temperature calcination to in situ generate polymeric phosphate on the catalyst surface.The surface polymeric phosphate succeed modification on NiO was evidenced by FT-IR and XPS characterizations.NiO-based catalysts have been recognized as great catalysts in oxidative dehydrogenation of propane(PODH)because of its excellent activity at low temperature.However,propane is easy to be over oxidized on the pure NiO and the propene selectivity is difficult to control especially in higher reaction temperature or conversion in PODH,thus the propene selectivity remains to be improved.In an attempt to control the selectivity,the as-synthesized polymeric phosphate modified NiO were used in this reaction.Experimental results and DFT calculations showed NiO-SPP was great effective in suppressing the adsorption of propene,therefore exhibiting a selectivity 2?3 times higher than NiO towards propene under the same conversion.Besides,NiO-SPP catalyst showed excellent catalytic stability.Resistance to sulfur poisoning of catalysts is an important yet challenging problem in methane combustion from the sulfur-containing exhaust.There is problem of sulfur poisoning over most Pd-based and metal oxides(NiO,Co3O4,et al.)catalysts with great activity.Although PtPd system catalyst can suppress of sulfur poisoning to some extent,the cost is large and the sulfur tolerance remains to be improved.Here NiO-SPP was prepared for methane combustion in the presence of SO2 and H2O.Catalytic results showed NiO-SPP was great sulfur tolerance with considerable activity.NiO-SPP plays two roles in the reaction.First,the enhanced NiO-polymeric phosphate interfacial action stabilizes the NiO NPs with great antisintering property.Second,surface polymeric phosphate suppresses the SOx adsorption during the reaction thus the formation of sulfates on NiO surface can be restricted after modification,thereby showing outstanding sulfur tolerance.These were confirmed by FT-IR,XPS,SEM,EDX-mapping characterizations and DFT calculations.