Aqueous‐Phase Hydrogenation of Acetic Acid over Transition Metal Catalysts

Abstract

Increases in the cost of petroleum combined with growing concerns for CO 2 emissions are prompting researchers worldwide to search for renewable sources of liquid fuel. In this respect, biomass is currently the only sustainable source of organic carbon, and biofuels are currently the only sustainable source of liquid fuels. [1] The challenge with biomass conversion into liquid fuels is that efficient processes are not yet economically viable.A large number of processes for converting biomass into biofuels involve hydrogenation of biomass-derived feedstock in the aqueous phase. These include hydrogenation of biooils, [2,3] hydrogenation of fermentation broths, [4] and alkane production by aqueous phase processing. [5,6] Hydrogenation of organic acids, which are produced in fermentation, results in a 50 % increase in ethanol yield compared to when ethanol is produced directly from fermentation. [7] Upgrading bio-oils by hydrotreating involves hydrogenating a range of functional groups, which also include organic acids. In fact, one of the slowest steps in the hydrotreating of bio-oils is the hydrogenation of organic acids. [3] For these hydrotreating routes to become economically viable, it is critical to design highly active and selective catalysts for aqueous-phase hydrogenation (APH) reactions. So far there has been no systematic study for the APH of acetic acid on monometallic catalysts.Herein we report the findings of a combined experimental and theoretical study on the APH of acetic acid catalyzed by transition metals such as Ru, Rh, Pd, Ni, Cu, Ir, and Pt. Significantly different activities for the conversion of acetic acid have been observed over these metals. High selectivities for ethanol were obtained for several of them; in particular, Ru showed approximately 80 % ethanol selectivity at moderate temperatures. Density functional theory (DFT) calculations suggested that the different activity can be attributed to the intrinsic reactivity of the metals for dissociating acetic acid or acetate to acetyl (CH 3 O), and a simple empirical correlation is identified that may be used to readily estimate the free energy of the transition state (TS) for the rate-limiting step in acetic acid conversion based on the adsorption energies of acetyl and hydroxy groups. These findings offer clues for designing [8][9][10] active and selective transition metal catalysts for the hydrogenation of organic acids and oxygenates in general.The activity of the APH of acetic acid has been measured for Ru/C, Pt/C, Pd/C, Rh/C, Ir/Al 2 O 3 , Raney Ni, and Raney Cu catalysts at temperatures from 110-290 8C, and at 5.17 MPa total pressure. The catalytic activity of each catalyst was measured at acetic acid conversion of less than 25 % in the absence of diffusion limitations (see the Supporting Information for Weisz modulus calculations). Figure 1 shows the turnover frequencies (TOFs) as a function of temperature for the total conversion of acetic acid. The TOFs of acetic acid conversion decrease in the order Ru > Rh % Pt > Pd % Ir > Ni >...

Reduced Carbon Dots versus Oxidized Carbon Dots: Photo‐ and Electrochemiluminescence Investigations for Selected Applications

“…15 The selective hydrogenation of carboxylic acids to their corresponding alcohols or diols is a very important direction in the biomass refinery. For example, the selective hydrogenation of acetic acid, propanoic acid, lactic acid and succinic acid from the fermentation of biomass can produce ethanol, 5 propanol, 6 1,2-20 propanediol 7 and 1,4-butanediol. [8][9][10] These compounds can be used as biofuel or monomers for the production of polyesters.…”

“…This result is consistent 60 with the previous work of Huber group. 5 In contrast, higher acetic is very important for the hydrogenation of carboxylic acid. 11 Subsequently, we also explored the possibility to use RhMoO x /SiO 2 catalyst for the aqueous phase hydrogenation of other biomass derived carboxylic acids.…”

Hydroconversion of acetic acid over indium- and phosphorus-modified nickel/laponite catalysts

“…Nickel and indium can form seven intermetallic compounds, such as, NiIn, Ni 2 In, Ni 3 In, Ni 4 In, Ni 2 In 3 and…”

Acetic acid hydroconversion over mono- and bimetallic indium doped catalysts supported on alumina and silicas of various textures

“…The significance of catalytic reduction of bioacids to fuel or intermediate material production is steadily increasing, however, only a few studies have been devoted to the acetic acid (AA) transformation [3,[7][8][9]. The literature describes catalysts for AA hydrodeoxygenation (HDO) comprised of one or more noble metals of Group VIII dispersed on oxides of elements of Group III/A or IV/A.…”