The catalytic cracking process involves the presence of acid catalysts (usually solid acids such as silica-alumina and zeolites), which promote a heterolytic (asymmetric) breakage of bonds yielding pairs of ions of opposite charges, usually a carbocation and the very unstable hydride anion.
ðə kˌæɾɐlˈɪɾɪk kɹˈækɪŋ pɹˈɑːsɛs ɪnvˈɑːlvz ðə pɹˈɛzəns ʌv ˈæsɪd kˈæɾɐlˌɪsts jˈuːʒuːəli sˈɑːlɪd ˈæsɪdz sˈʌtʃ ɐz sˈɪlɪkəɐlˈuːmɪnə ænd zɪˈɑːlaɪts, wˌɪtʃ pɹəmˈoʊt ɐ hˌɛɾɚɹəlˈɪɾɪk ˌeɪsɪmˈɛtɹɪk bɹˈeɪkɪdʒ ʌv bˈɑːndz jˈiːldɪŋ pˈɛɹz ʌv ˈaɪɑːnz ʌv ˈɑːpəzˌɪt tʃˈɑːɹdʒᵻz, jˈuːʒuːəli ɐ kˌɑːɹbəkˈeɪʃən ænd ðə vˈɛɹi ʌnstˈeɪbəl hˈaɪdɹaɪd ˈænaɪən.