Reliable procedure for the synthesis of Ni-SAPO-34 as a highly selective catalyst for methanol to ethylene conversion

A reliable synthetic procedure of Ni-SAPO-34 crystals having the catalytic performance for methanol to ethylene with a selectivity as high as 88% was investigated. The focus of the study was put on the increase in homogeneity of the mixed gel as the precursor of crystallites. Proper treatments of the mixed gel such as application of ultrasonic waves, addition of a proper amount of the seed crystals and milling were found to be important to obtain a high crystallinity and a sharp distribution of crystal size. Incorporations of the crystal ingredients, P, Si, and Ni, into the framework of SAPO-34 were observed for those crystallites. The crystallites, which were 0.85 +/- 0.05 mu m in size and had a solid acid density 4 mu mol/m(2) distributed inside the crystallites, exhibited the highest ethylene selectivity, 88%. The total conversion level of methanol was observed at a medium reaction temperature around 425 degrees C. These crystallites exhibited a minor deactivation due to the lower amounts of coke formation. (C) 1997 Elsevier Science B.V.