Preparation And Application Of Hydrophobic Activated Carbon Supported Acid-resistant Nickel-based Catalysts

Nickel catalysts are commonly applied into all kinds of reactions such as steam reforming,decomposition of ammonia,catalytic oxidation,catalytic hydrogenation,et al,owing to their low price and high catalytic activity.As industrial catalysts,the high stability of the catalysts is important besides excellent activity.Nickel catalysts generally show excellent catalytic activity for the hydrogenation of acidic substances,however,their stability is very poor due to being oxided quickly by the acidic substances and reaction water.Therefore,it is necessary and promising to develop acid-resistant nickel-based catalysts.In the present paper,hydrophobic activated carbon supported Ni catalysts doped with Fe,Mn and Mo were prepared by incipient wetness impregnation method.The liquid phase selective hydrogenation of phthalic anhydride to phthalide was applied for investigating the activity,selectivity and stability of the catalysts.The effects of promoters,nickel loading and the treatment of activited carbon on the catalytic performance of nickel-based catalysts were investigated.The catalysts were characterized by using BET,XRD,SEM,TEM,XPS and TG techniques.The resuts showed that among the catalysts studied,NaBH₄ pretreated activated carbon supported 15Ni-5Fe catalyst?named as 15Ni-5Fe/AC-NaBH₄.which contains 5 wt.%of Fe and 15 wt.%of Ni?showed the best catalytic for hydrogenation of phthalic anhydride to phthalide.The conversion of phthalic anhydrides and the selectivity to phthalide were 100%and 95.2%,respectively,at 180? and 4.0 MPa.Moreover,the 15Ni-5Fe/AC-NaBH₄ catalyst could be recycled for more than 8 times with less decrease in activity,which was much superior to those of the commercial Raney Ni and the Ni/activated carbon catalyst without hydrophobilization.The high recyclability of the 15Ni-5Fe/AC-NaBH₄ catalyst could be contributed to the reasons as follows:?1?the addition of Fe could disperse the electron clouds around Ni atoms,which might stabilize the catalyst;?2?the application of the reduced activated carbon as a hydrophobic support could rule out reaction water from the metal surface,which might reduee the eorrosion of Ni as the activity of the HT concentration decreases.In order to futher investigate the acid-resistence of the catalyst,the 15Ni-5Fe/AC-NaBH₄ catalyst was used to the liquid hydrogenation of levulinic acid?LA?,succinic acid?SA?,maleic acid?MA?and trimellitic anhydride?TMA?.The results showed that 15Ni-5Fe/AC-NaBH₄ catalyst could reuse five times in the hydrogenation of LA?T=140?,P=4.0 MPa,t=6.0 h,methanol as solvent?,keeping 100%of conversion and 80%of selectivity to ?-valerolactone.Moreover,the catalyst showed high stability for the hydrogenation of MA and SA?reaction condition:T=200?,P=4.0 MPa,t=4.0 h?,with 100%of conversion and above 70%of selectivity to ?-butyrolactone after being reused 5 times.In solvent-free hydrogenation of TMA,the activity of the 15Ni-5Fe/AC-NaBH₄ catalyst gradually decreased with the reuse time,and the color of the reation solution turned from black to gray,which indicated that nickel was oxided.The deactivation of the 15Ni-5Fe/AC-NaBH₄ catalyst was mainly ascribed to the leaching of active nickels corroded by H⁺ from TMA.