Steam reforming of diethyl ether, ethanol and n-butanol with varied functionality and carbon chain impacts evolution of reaction intermediates and coking behaviors

Molecular structures of organics play key roles in determining the tendency of coking and property of coke through governing reaction intermediates formed. Diethyl ether (DEE) can be produced from etherification of ethanol and has same carbon number with n-butanol (butanol), while they may show distinct coking behaviors in steam reforming (SR). Herein, SR of DEE, ethanol and butanol over Ni/SBA-15 catalyst were performed, aiming to probe impacts of ether functionality and length of carbon chain of the alcohols on coke formation. The results indicated that cracking of DEE formed CxHy* species and unsaturated ketone intermediates, serving as precursors of coke. Dissociative adsorption of butanol formed abundant CxHy* species even from 100 degrees C, due to its longer carbon chain and lower oxygen content. In comparison, abundant oxygen-containing intermediates were generated from degradation of ethanol and reactions with steam. Abundant CxHy* species from DEE and butanol prompted formation of more coke than that from ethanol (60.6 % of coke in the catalyst for DEE, 66.8 % for butanol and 32.9 % for ethanol). Moreover, the coke from SR of ethanol was thermally less stable than that from DEE or butanol, due to the involvement of more oxygen-containing intermediates, which resulted in more aliphatic coke of amorphous form in ethanol reforming. Additionally, the coke from DEE reforming was more defective with carbon nanotube form of thick walls and little internal cavity. The coke produced from butanol reforming was more graphitic and mainly in carbon nanotube form of smooth surface. Varied abundance of CxHy* and ketone species in reforming of DEE and butanol created such a difference.