A hydrocarbon conversion catalyst composition, useful for paraffin-olefin alkylation, can comprise a three dimensional crystalline zeolite molecular sieve having a pore size large enough to adsorb 2,2,3-trimethylpentane and having a composition expressed in terms of mole ratios of oxides as [equation included]
wherein I represents a monovalent metal cation; II represents a divalent metal cation; III represents a trivalent metal cation; IV represents a tetravalent cation; a has a value of from zero to 0.15; b has a value of from zero to 0.75; c and d each have values of from zero to 1; e has a value of from 2 to 20; with the proviso that when e has a value of from 2 to 3, the value of ((b+c)=0.75 to 1 and d=0; and with the proviso that when e has a value of > 3 to 4, the value of (b+c+d)=0.6 to 1.0; and with the further proviso that when e has a value of > 4 to 20, the value of (b+c+d)=0.25 to 1.0. In one embodiment said zeolite contains less than about 60 percent of its maximum OH exhibiting infrared absorption in the region of 3480 to 3670 cm..sup.-1 ; however in a slurry-reaction process the preferred catalysts have been activated at a temperature in the range of 400.degree.-500.degree. C. and contain about said maximum OH absorption. In the above catalyst, protons and/or ammoniumions can be present to preserve electronic equivalency. The degree of conversion of olefins and paraffins to saturated products can be increased by incorporation into the catalyst of a halide adjuvant containing bromine, chlorine or fluorine. One preferred catalyst can be represented, by the above formula as [equation included]
where I is Na.sup.+ and III is a trivalent rare earth metal, such as Ce.sup.+3. More precisely, this catalyst can be represented as 0.1(Na.sub.2 O):0.2(H.sub.2 O):0.7(III.sub.2/3 O):Al.sub.2 O.sub.3 :4.7SiO.sub.2.