The Role of Copper in the Upgrading of Bioalcohols

Some recent results on Guerbet reactions are reported and a short review on dehydrogenative coupling of alcohols (DHC) is presented. The focus of this Minireview is on the role of acidic and basic sites and, in particular, on the role of Cu if it is present in the catalyst, taking into account that the two processes share the first step, namely alcohol dehydrogenation, whereas the second one is determining in driving selectivity towards self-coupling or symmetrical ester formation. The main type of catalysts for the Guerbet reaction are based on hydrotalcites, hydroxyapatite and supported metal systems, whereas the catalysts for DHC are copper catalysts on different supports. The role of acidic and basic sites in determining activity and selectivity to Guerbet alcohols has been investigated and quite stringent requirements for the selectivity of the reaction have been highlighted. For DHC, we have focused on the role of the interaction of copper with the support, which in turn influences the distribution of acidic and basic sites. The morphology of the metallic phase has been suggested as a distinctive factor in promoting C-C coupling or C-O coupling in the second step for Cu-containing catalysts.