Nitrogen resistant paraffin hydroisomerization catalysts

A process for paraffin isomerization of a distillate range hydrocarbon feedstock having a boiling range of from about 330.degree. F.-650.degree. F. and a paraffinic content of molecules with not more than about 20 carbon atoms, and containing nitrogen impurities of at least 20 ppm, comprising:

• contacting said paraffin-containing feedstock with a catalyst including a crystalline zeolite catalyst having pore openings defined by:
• (1) a ratio of sorption of n-hexane to o-xylene, on a volume percent basis, of greater than about 3, which sorption is determined at a P/P.sub.o of 0.1 and at a temperature of 50.degree. C. for n-hexane and 80.degree. C. for o-xylene and (2) by the ability of selectively cracking 3-methylpentane (3MP) in preference to the doubly branched 2,3dimethylbutane (DMB) at 1000.degree. F. and 1 atmosphere pressure from a 1/1/1 weight ratio mixture of n-hexane/3-methyl-pentane-2,3dimethylbutane, with the ratio of rate constants k.sub.3MP /k.sub.DMB determined at a temperature of 1000.degree. F. being in excess of about 2, said catalyst including a Group VIII metal, and having a zeolite SiO.sub.2 /Al.sub.2 O.sub.3 ratio of at least about 20:1, said contacting made at a temperature of from about 390.degree. F. to about 850.degree. F. and a pressure of from about 100 psig to about 1,000 psig.