## 1 Introduction  
The conversion of bio-ethanol to butanol as additive for gasoline has been recently investigated in order to upgrade one of the products of (Acetone Butanol Ethanol) ABE fermentation of biomass into a higher fuel-soluble alcohol with a greater calorific value [1]. Coupling of ethanol takes place according to the Guerbet reaction, generally through a catalytic pathway [2]. Catalysts proposed for the Guerbet reaction are supported metals (Ru, Rh, Pd, Pt, Au, Ni, Ag), hydroxyapatite (HAP), and basic oxides as MgO [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13]. Our preliminary studies [14] highlighted the key role of basic sites and high surface area of the catalyst to obtain better performance. In agreement with this finding, [PERSON] et al. [15] proposed that strong basic sites facilitate the formation of butanol, presumably through a coupling reaction giving the aldol condensation, while inhibiting the C-C coupling reactions to C6 and heavier compounds that deactivates the catalyst at high temperature. [PERSON] et al. [16] reported that dehydrogenation is the first step of the Guerbet coupling over MgO forming a carbonyl intermediate. [PERSON] et al. [17] proposed that, in the absence of metal promoters, ethanol dehydrogenation on basic metal oxides proceeds through an E1 cB mechanism described as an initial dissociative adsorption of the alcohol on weak Lewis acid-strong Bronsted base pairs (Mg(A)-O) which break the OH bond forming a surface alkoxide intermediate [13]. In a recent paper [18], we demonstrated that dispersion of unpromoted or metal-promoted MgO on high surface area alumina pellets provided better results compared to the corresponding metal/MgO powder catalysts showing a lower surface area. The increase of surface area of MgO dispersed on \(\gamma\)-Al\({}_{2}\)O\({}_{3}\) was also associated with a greater number of basic sites evaluated through CO\({}_{2}\) Temperature Programmed Desorption (TPD) tests. All these results suggest that a higher dispersion of MgO and, consequently, a higher exposure of hydroxyl groups, can increase the number of sites activating the ethanol molecule thus improving conversion. To this purpose, in this work, dispersion of MgO on a support with a larger surface area was proposed in order to further improve the catalytic performance. A cheap and easily available support, such as activated carbon (AC), was chosen to limit the costs of the overall process of production of butanol from bio-ethanol which also includes distillation of ABE mixture. To the best of our knowledge, activated carbons have never been used for the Guerbet reaction whereas MgO dispersed on activated carbons has been proposed as sorbent for different gaseous species, such as CO\({}_{2}\)[19], H\({}_{2}\)S [20; 21], and organics [22; 23] strongly increasing the adsorption capacity of the raw activated carbon. Another issue related to the use of catalysts for Guerbet reaction is their possible deactivation in the presence of water. This represents an important concern for catalysts operating directly on the ABE mixture but also for systems proposed for the use downstream the separation of ethanol from the other components of the ABE mixture. Indeed, under real conditions, in order to limit costs, the azeotropic mixture (96% ethanol, 4% water) produced after distillation of ABE mixture can reasonably represent the feed. [PERSON] et al. [24] proposed a water-tolerant catalyst based on Ni/MgO/SiO\({}_{2}\) for ABE conversion into high-value bio-fuels as C\({}_{5}\)-C\({}_{15}\) ketones and alcohols due to the high stability of magnesium silicate structure compared to that of hydrol calcite, more commonly used for this reaction. Nevertheless, in all studies focused on the Guerbet reaction, the feed consisted of dry ethanol/inert gas mixture.