Investigating the multifunctional nature of bimetallic FeMoP catalysts using dehydration and hydrogenolysis reactions

Abstract

Herein, we investigate the effects of altering the multifunctional nature of a series of FeMoP catalysts for biomass deoxygenation reactions. Unsupported FeMoP catalysts were synthesized at reduction temperatures between 650 °C and 850 °C. The reduction temperature used during the synthesis of FeMoP altered the surface properties of these materials (i.e., acidity and CO-titrated metal sites) while leaving the bulk crystal structure of FeMoP unaffected. This alteration in the surface properties significantly affected the catalytic performance of FeMoP materials in the deoxygenation reactions. The catalytic performance of the FeMoP catalysts was first investigated using the acid catalyzed, non-aqueous, dehydration of cyclohexanol. Aside from showing high selectivities to cyclohexene (> 99 %) for all catalysts, the experiments demonstrated that FeMoP-650 showed the highest initial rate due to the largest number of surface acid sites among these catalysts. In addition, these FeMoP catalysts were examined using the hydrodeoxygenation (HDO) of phenol. While all FeMoP catalysts were highly selective to benzene (~ 90 %) at conversions less than 10 %, studies at higher conversions of phenol provided evidence that catalysts with a higher amount of acid sites maintained enhanced selectivity to benzene. Furthermore, the stability of FeMoP catalysts for phenol HDO was tested with a 48-hour time-on-stream (TOS) study. FeMoP exhibited excellent stability, as evidenced by the retention of the initial reaction rate, selectivity to benzene, and oxidation state of surface species throughout the TOS run.

Dynamics of carbon formation during the catalytic hydrodeoxygenation of raw bio-oil

“…This work has been carried out with the nancial support of the Ministry of Economy and Competitiveness of the Spanish Government, some co-founded with ERDF funds (CTQ2015-67425-R, CTQ2016-79646-P), the Basque Government (IT1218- 19), and the European Commission (Horizon H2020-MSCA RISE-2018, Contract No. 823745).…”

“…16,17 The higher HDO activity of phosphided catalysts is related to the presence of P-OH groups which act as Brønsted sites, providing active hydrogen. 18 Unsupported FeMoP catalysts were reported by Rensel et al 19,20 as highly selective materials towards aromatic compounds, also with a high catalyst stability and recyclability. In a complementary study, they correlated the Lewis acidity of Fe x Mo 2Àx P catalyst with the lower activation energy required for the C-O bond cleavage in phenol HDO.…”

Hydrodeoxygenation of raw bio-oil towards platform chemicals over FeMoP/zeolite catalysts

“…A favorable synergy for achieving high selectivity towards aromatics from aryl ethers and phenol was attained by Rensel et al [28,29] using unsupported FeMoP catalysts, also demonstrating the stability of these catalysts in a reaction medium with high water content. In a study on the structural properties of FexMo2-xP catalysts, they also correlated the lower activation energy required for the cleavage of the C-O bond in phenol with the Lewis acidity of these catalysts, which enhance the elongation of these linkages [30].…”

Periodic Trends from Metal Substitution in Bimetallic Mo-Based Phosphides for Hydrodeoxygenation and Hydrogenation Reactions

“…Metal phosphides are also well suited for HDO reactions due to their multifunctional nature, which also results in the ability to catalyze a variety of other reactions pertaining to biomass upgrading. In our previous work, we showcased the multifunctionality of FeMoP for both the HDO of phenol and the acid-catalyzed dehydration of cyclohexanol . FeMoP catalyzed the dehydration of cyclohexanol to cyclohexene in the absence of H 2 using the presence of surface acid sites (i.e., Lewis and Brønsted) to promote the reaction .…”