The Effects of Dopants on the Cu–ZrO₂ Catalyzed Hydrogenation of Levulinic Acid

Abstract

Catalytic hydrogenation of levulinic acid to form γ-valerolactone was studied over Cu-ZrO2 catalysts doped with metal oxides from the first row transition metals. The Cu-ZrO2 material was prepared by oxalate gel co-precipitation and dopants were added by an incipient wetness approach. The addition of 1% Mn into Cu-ZrO2 significantly increases the yield of γ-valerolactone and the catalytic activity of Mn/Cu-ZrO2 was found to be 1.6 times higher than that of the undoped Cu-ZrO2 catalyst. Catalyst characterization suggests that the Mn dopant improves the dispersion of Cu on the surface of ZrO2. Kinetic studies show that the reaction order with respect to the substrate concentration is approximately zero. However, the order of reaction with respect to the partial pressure of H2 is different for the Mn/Cu-ZrO2 and Cu-ZrO2 catalysts. Comparison of reaction products from reactions carried out in H2O and D2O solvents using 1 H NMR and 13 C NMR show that there is a pre-equilibrium keto-enol isomerisation step under our reaction conditions. DFT calculations show that the enol isomers have a higher affinity for the Cu surface which may improve the availability of the substrate in the hydrogenation step of the reaction.

The hydrogenation of levulinic acid to γ-valerolactone over Cu–ZrO2 catalysts prepared by a pH-gradient methodology

“…Even so, additional cycling experiments ( Fig. 4 b) confirmed that the catalytic performance of the 30 mol% catalyst remained reasonably constant for up to 4 uses, which is a marked improvement compared with other Cu-ZrO 2 catalysts we have investigated previously (activity drop of up to 30% after 1 use) [28,32] . Perhaps most interestingly, SEM confirmed that there was severe change in the surface morphology of the catalyst upon subsequent uses, see Fig.…”

“…Another study reported that the deposition of Pd onto a Cu-ZrO 2 could result in sequential reaction to produce 1,4-pentanediol and 2-methyl tetrahydrofuran [27] . We too have investigated how the doping of a secondary transition metal onto a Cu-ZrO 2 catalysts affects the performance [28] . Of the metals tested, only Mn provided a promotional effect which was established to be due to an increase in the rate of dissociative H 2 adsorption over the catalyst.…”

Selective Transformations of Triglycerides into Fatty Amines, Amides, and Nitriles by using Heterogeneous Catalysis

“…The alarming predictions of the rapid depletion of fossil‐fuel resources have inspired researchers to develop alternative technologies that exploit renewable energy sources . Many studies have focused on the conversion of lignocellulosic biomass and triglycerides into various platforms of value‐added chemicals . Industrially, triglycerides in oils and fats have been used as feedstocks for the synthesis of fatty amines, amides, nitriles, and alcohols, which in turn are used for the production of surfactants, polymers, and other useful commodity chemicals …”

Drastic change in selectivity caused by addition of oxygen to the hydrogen stream for the hydrogenation of nitrite in water over a supported platinum catalyst

“…Selective hydrogenations over supported metal catalysts have been extensively studied since the discovery of the Lindlar catalyst for the hydrogenation of alkynes 1 because it is invaluable for the synthesis of various chemicals [2][3][4] as well as environmental purification. [5][6][7][8][9][10] A research goal in hydrogenation is to achieve high selectivity by optimizing the reaction conditions [11][12][13] in conjunction with catalyst design, wherein scientists search for the best combination of metal and support, [14][15][16][17] the addition of promoters, [18][19][20][21] and applying special preparation techniques and conditions.…”