Aqueous-phase hydrodeoxygenation of carboxylic acids to alcohols or alkanes over supported Ru catalysts
Graphical abstract
The hydrodeoxygenation routes of carboxylic acids over the supported Ru catalysts was elucidated: the CO hydrogenation of acyl intermediate gives the production of alcohol, the C–C bond cleavage gives the adsorbed CO and hydrocarbon moieties by the decarbonylation of acyl intermediate, and then the adsorbed CO and hydrocarbon moieties hydrogenate to methane and Cn−1-alkane.
Highlights
► The APHDO of carboxylic acids was studied over the supported Ru catalysts. ► The C–C bond cleavage reaction is derived from the decarbonylation of acyl. ► The C–C bond cleavage reaction is dominant over the Ru/ZrO2 at high temperature. ► The C–C bond cleavage reaction is greatly inhibited over the Ru/Al2O3. ► The C–C bond cleavage or CO hydrogenation strongly depends on the nature of support.
Introduction
Biomass is a promising candidate to serve as a sustainable source of organic carbon for the production of industrial chemicals [1]. The available strategies for transforming biomass to bio-fuels and/or chemicals have been attracted more interestingly. In future, the range of block chemicals from biorefineries is extensive and is expected to become greater with further research [2], [3], [4], [5]. Generally, these block chemicals, i.e., the so-called platform molecules, are defined as chemicals containing multiple functional groups (e.g., acids, ketones, alcohols, amines, etc.). It is imperative to develop more efficient processes for catalytic upgrading of these block chemicals. However, lots of potential feedstocks are produced along with water from biomass by fermentation and/or hydrolysis routes [4]. However, removal of water from these compositions would be time-consuming and costly, and water has many advantages over more conventional solvents that present problems with toxicity and difficulties with handling and disposal. Considering these factors, the aqueous-phase hydrodeoxygenation (APHDO) reactions [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21] are a crucial component of a number of strategies for the conversion of biomass-derived feedstocks into fuels and chemicals, e.g., hydrogenation of targeted functionalities of biomass including acids, sugars, aldehydes and furans. Many groups have extensively worked on these (e.g., Dumesic [8], [9], [10], [11], [15], [20], [22], Miller and Jackson groups [6], [7], [12], [13], [23], Huber [17], [20], [22], [24], [25], [26], [27], [28], Corma [29], Clark and Luque groups [30], [31]), including alcohol production from organic acids [6], [12], [17], [23], gasoline production from bio-oils [28], and alkane production from carbohydrates [8], [11], [20], [22].
The APHDO of carboxylic acids to alcohols has been investigated as a possible pathway for production of novel, high-valued products from bio-derived feedstock [23]. The direct APHDO of organic acids offers an alternative that is atom economical and amenable to continuous processing, and that obviates the need for intermediate esterification, use of organic solvents, and byproduct waste streams [23]. Recently, Miller and Jackson groups have studied the APHDO of propanoic acid and lactic acid over the Ru/C catalyst [6], [12], [13]. They demonstrated that production of alcohol was improved at lower temperature and higher hydrogen pressures, and the methane, ethane and propane were detected as the main by-products. In addition, many degraded alkane byproducts were produced in the hydrogenolysis of glycerol to propylene glycol over the Ru-base catalysts [32], [33], [34], [35]. In these reactions, the cleavage of C–C bonds and the formation of methane were proposed to occur primarily through a metal-catalyzed reaction on Ru [33]. Thus, selectively removing oxygen from the biomass-derived compounds is one of the key challenges in converting renewable biomass resources into fuels and chemicals. The oxygen is removed from the biomass with the APHDO by a combination of the CO hydrogenation, the C–O bond cleavage and the C–C bond cleavage reactions. If the larger alkanes or upgraded oxygenates are desired, then the C–C bond cleavage should be inhibited and the CO hydrogenation and the C–O bond cleavage should be strengthened. If the degraded alkanes are desired, then the C–C bond cleavage should be enhanced. Therefore, it is necessary to understand the CO hydrogenation and C–C bond cleavage reactions over the supported Ru catalysts, since the ruthenium is a promising catalyst for the conversion of biomass feedstock to various chemicals [6], [12], [13], [31], [32], [33], [34], [35], [36], [37].
In this work, the APHDO of carboxylic acids (C2–C4), especially propanoic acid served as a probe molecule, was studied to understand the catalytic performance of several supported Ru catalysts (Ru/C, Ru/ZrO2 and Ru/Al2O3). The goal was to identify key reaction intermediate and to reveal the reaction mechanisms of the CO hydrogenation and C–C bond cleavage on supported Ru catalysts. The different reaction routes (CO hydrogenation of carboxyl and C–C bond cleavage) were investigated in detail. In particular, the DRIFTS of propanoic acid were performed to understand the mechanism of the C–C bond cleavage. The effect of support on the hydrodeoxygenation routes was discussed based on the characterizations of catalysts (H2-TPR, NH3-TPD, CO-FTIR and DRIFTS of propanoic acid). In the present contribution, the APHDO reaction can be tuned to make a targeted product (alkanes or upgraded oxygenates) from biomass-derived chemicals by the improvement in the catalyst design.
Section snippets
Catalyst preparation
Supported Ru catalysts were prepared by incipient wetness impregnation with an aqueous solution containing corresponding metal precursors (RuCl3·3H2O, Shaaxi Kaida Chemical Engineering Co., Ltd., China) at ambient for 12 h, followed by drying at 120 °C for 12 h. Subsequently, the catalysts were calcined at 500 °C in air for 6 h except the Ru/C catalyst. Prior to impregnation, the supports ZrO2 (SBET = 58 m2 g−1, Jiangsu Qianye Co., Ltd., China), γ-Al2O3 (SBET = 197 m2 g−1, Shandong Aluminum Co., Ltd.,
BET surface area and pulse chemisorption of H2 and CO
BET surface area and Ru dispersion of catalysts are shown in Table 1. The Ru/ZrO2 catalyst has a small BET surface area of 52 m2 g−1 compared with the Ru/C (1021 m2 g−1) and Ru/Al2O3 (185 m2 g−1) catalysts. The Ru dispersion determined by H2 or CO pulse chemisorption increases in the same order: Ru/Al2O3 < Ru/ZrO2 < Ru/C. Nevertheless, the Ru dispersion measured by H2 pulse chemisorption is lower than that determined by CO pulse chemisorption. This behavior may result from the strongly corrosive
Conclusions
For carboxylic acid APHDO over the Ru/C, Ru/ZrO2 and Ru/Al2O3 catalysts, the high temperature, as well as, the catalysts with high Ru loading Ru loading facilitated the cleavage of C–C bond, while acidic support in combination with a metal favored the hydrogenation of carboxyl. The DRIFTS results revealed that the C–C bond cleavage was induced by the decarbonylation of acyl on the catalyst. The C–C bond cleavage was favored in the order of Ru/C > Ru/ZrO2 > Ru/Al2O3. Based on H2-TPR, NH3-TPD and
Acknowledgements
The authors gratefully thank the financial supports of Major State Basic Research Development Program of China (973 Program) (No. 2012CB215305) and Natural Science Foundation of China (No. 20976185). We also thank Dr. Guoqiang Ding for valuable discussion during manuscript preparation.
References (72)
- et al.
Appl. Catal. A
(2001) - et al.
Catal. Today
(2007) - et al.
Catal. Commun.
(2009) - et al.
Bioresour. Technol.
(2008) - et al.
J. Catal.
(2010) - et al.
J. Catal.
(2010) - et al.
Catal. Today
(2006) - et al.
Appl. Catal. A
(2007) - et al.
Catal. Commun.
(2010) - et al.
Appl. Catal. A
(2007)
J. Catal.
Appl. Catal. B
J. Catal.
Catal. Today
Appl. Catal. B
Appl. Catal. A
Appl. Catal. A
Appl. Catal. A
Catal. Today
Surf. Sci.
J. Catal.
J. Catal.
Spectrochim. Acta Part A: Mol. Biomol. Spectrosc.
Appl. Surf. Sci.
Appl. Catal. B
Surf. Sci.
J. Catal.
Surf. Sci.
J. Catal.
Catal. Today
Appl. Catal. B
J. Catal.
J. Mol. Catal. A: Chem.
Surf. Sci.
ChemSusChem
Biofuels Bioprod. Bioref.
Cited by (136)
Hydro-deoxygenation of biofuel
2023, Bioenergy Engineering: Fundamentals, Methods, Modelling, and ApplicationsHydrodeoxygenation of 1,2-decanediol to produce 1-decanol over Cu/SiO<inf>2</inf>-Al<inf>2</inf>O<inf>3</inf> catalyst
2022, Applied Catalysis A: GeneralHighly active and stable Cu-MnO/SBA-15 catalyst for hydrogenation of acetic acid to ethanol: Experimental and DFT studies
2022, Journal of Environmental Chemical Engineering