Synergism in the actions of a transition metal cation and a Lewis acid in the liquid- and gas-phase catalytic conversion of alkanes over modified ZSM-5 zeolites under mild conditions

Unusual coordination state of cobalt ions in zeolites modified by aluminum chloride

“…DRIFT spectra of the Co-Z-ac and Al-Co-Z-ac were identified in earlier publication. 5 The impact of zeolite modification using cobalt acetate and aluminum chloride on hydroxyl cover of the support was very similar to the ones observed using cobalt chloride.…”

“…It should be noted that there is no such absorption band in the spectra of parent H-ZSM-5 zeolite modified only by AlCl 3 (Al-Z) without the Co introduction. 5 Thus, the spectra of the cobalt carbonyl complexes ( Fig. 2 and 3) indicate that the introduction of aluminum chloride generates new coordination states of the transition metal.…”

“…The FTIR spectra of the parent H-ZSM-5 zeolite and the cobalt containing samples prepared from cobalt chloride (Сo-Z-0.9-cl) and additionally modified with aluminum chloride (Al-Co-Z-0.9-cl) are compared in Fig observed changes likely arise from the formation of (-O-)AlCl x (х = 1 or 2) fragments bonded to silicon or aluminum atoms on the support surface via reaction (1). 5,31 In particular, the 3713 cm -1 band is assignable to vibrations of terminal Si-OH groups whose oxygen atom interacts with the extraframework Al atom of a (-O-)AlCl x fragment anchored to adjacent Si or Al atoms. A similar coordination of terminal Si-OH groups with extraframework aluminum atoms shows itself in the spectrum of HZSM-5.…”

“…CO adsorption on the acid sites of HZSM-5, as we have shown early5 , was observed in DRIFT spectra at RT only at pressures more than 0.7 kPa, including a band at 2169 cm -1 , which is due to the Hcomplexes of carbon monoxide with bridging protons of acidic Si-OH-Al groups[23][24][25][26] , and weak bands at 2189 and 2221 cm -1…”

“…3,4 It was found recently that highsilica zeolites modified with cobalt salts and aluminum chloride were one order of magnitude more active and selective for paraffin conversion in the liquid phase at medium temperatures (130-190 °C) than the parent support. 5 The synergistic action of Lewis acids and transition metal salts is also known for the catalytic isomerization of alkanes, the alkylation of unsaturated and aromatic compounds, and in the cracking of heavy paraffins. [6][7][8][9] This effect is commonly attributed to the formation of complexes that are more acidic than the initial Lewis acid.…”