Green Diesel Production over Nickel-Alumina Nanostructured Catalysts Promoted by Copper

Abstract

A series of nickel–alumina catalysts promoted by copper containing 1, 2, and 5 wt. % Cu and 59, 58, and 55 wt. % Ni, respectively, (symbols: 59Ni1CuAl, 58Ni2CuAl, 55Ni5CuAl) and a non-promoted catalyst containing 60 wt. % Ni (symbol: 60NiAl) were prepared following a one-step co-precipitation method. They were characterized using various techniques (N2 sorption isotherms, XRD, SEM-EDX, XPS, H2-TPR, NH3-TPD) and evaluated in the selective deoxygenation of sunflower oil using a semi-batch reactor (310 °C, 40 bar of hydrogen, 96 mL/min hydrogen flow rate, and 100 mL/1 g reactant to catalyst ratio). The severe control of the co-precipitation procedure and the direct reduction (without previous calcination) of precursor samples resulted in mesoporous nano-structured catalysts (most of the pores in the range 3–5 nm) exhibiting a high surface area (192–285 m2 g−1). The promoting action of copper is demonstrated for the first time for catalysts with a very small Cu/Ni weight ratio (0.02–0.09). The effect is more pronounced in the catalyst with the medium copper content (58Ni2CuAl) where a 17.2% increase of green diesel content in the liquid products has been achieved with respect to the non-promoted catalyst. The copper promoting action was attributed to the increase in the nickel dispersion as well as to the formation of a Ni-Cu alloy being very rich in nickel. A portion of the Ni-Cu alloy nanoparticles is covered by Ni0 and Cu0 nanoparticles in the 59Ni1CuAl and 55Ni5CuAl catalysts, respectively. The maximum promoting action observed in the 58Ni2CuAl catalyst was attributed to the finding that, in this catalyst, there is no considerable masking of the Ni-Cu alloy by Ni0 or Cu0. The relatively low performance of the 55Ni5CuAl catalyst with respect to the other promoted catalysts was attributed, in addition to the partial coverage of Ni-Cu alloy by Cu0, to the remarkably low weak/moderate acidity and relatively high strong acidity exhibited by this catalyst. The former favors selective deoxygenation whereas the latter favors coke formation. Copper addition does not affect the selective-deoxygenation reactions network, which proceeds predominantly via the dehydration-decarbonylation route over all the catalysts studied.

Mineral Montmorillonite Valorization by Developing Ni and Mo–Ni Catalysts for Third-Generation Green Diesel Production

“…The intermediates (fatty acids and fatty acid–fatty alcohol esters) and final products (n-alkanes) are compatible with the SDO network over the nickel catalysts described in detail in the Introduction ( Figure 1 ). Moreover, the reaction kinetics curves (amount of a given product versus time) ( Figure 12 ) pass through a maximum for the intermediate products, whereas they increase monotonically for the n-alkanes, in line with the well-established network over nickel catalysts ( Figure 1 ) [ 11 , 43 ]. This clearly shows that this network is also valid for nickel catalysts supported on mineral montmorillonite.…”

“…Inspection of Figure 14 b shows that an increase in the reaction temperature favors the production of hydrocarbons with an even number of carbon atoms, implying a shift of the SDO pathway from the decarbonylation of the intermediate aldehydes to the dehydration of the intermediate alcohols. Moreover, this can be related to the decrease in the amount of esters with increasing reaction temperature, as the SDO of the intermediate esters favors the production of hydrocarbons with even numbers of carbon atoms (see the SDO network in Figure 1 and [ 22 , 43 ]). The production of C18 and C16 hydrocarbons instead of C17 and C15 hydrocarbons is obviously beneficial from the viewpoint of carbon atom economy.…”

“…TG, TG S , DG S , MG S , PE and ME are the initial triglycerides, the saturated triglycerides, the saturated diglycerides, the saturated monoglycerides, the propyl-esters and the methyl-esters, respectively. The other molecules are represented by their chemical formulas [ 43 ]. (Molecules written in green, red and blue are final, intermediate and gas-phase products, respectively).…”

“…The research development, reviewed up to 2016 by our group [ 11 ], continues intensively today. The SDO proceeds through the following reaction network over the metallic nickel nanoparticles ( Figure 1 ) [ 11 , 22 , 43 ]: the unsaturated side chains of triglycerides are quickly saturated, and this is followed by the rapid progressive decomposition of the O-C bonds on the glycerol backbone side, resulting in di- and mono-glycerides and then propane, releasing one molecule of fatty acid after each decomposition. The fatty acids might then be decarboxylated to n-alkanes and/or hydrogenated/dehydrated to fatty aldehydes, which then are decarbonylated to n-alkanes.…”

Theoretical Investigation of the Deactivation of Ni Supported Catalysts for the Catalytic Deoxygenation of Palm Oil for Green Diesel Production

“…Heterogeneous catalysts are cheaper, less corrosive, environmentally friendly and are easily regenerated, recovered and reused [4]. Nickel-supported catalysts have attracted great attention in recent years for green diesel production [2,3,[5][6][7][8][9][10][11][12][13][14][15][16]. Catalyst deactivation is a troublesome issue when investigating the hydroprocessing of triglycerides.…”