Ethanol conversion into 1,3-butadiene over a mixed Hf-Zn catalyst: A study of the reaction pathway and catalyst deactivation

•A detailed reaction network for one-step ethanol-to-1,3-butadiene conversion on mixed Hf-Zn catalyst is obtained.•Catalyst deactivation by deposition of aromatic-type coke and reduction of Zn2+ sites to Zn0 with TOS.•Zn2+ reduction induces Zn2+/Hf4+ site misbalance, altering catalyst selectivity with TOS.•Calcination with air removes coke and re-oxidizes part of Zn0 back to Zn2+ but Zn2+/Hf4+ site balance is not re-established.•The suitability of by-product recycling for process design is assessed by experiments co-feeding by-products and ethanol.