Selective deoxygenation of aldehydes and alcohols on molybdenum carbide (Mo2C) surfaces

doi:10.1016/j.apsusc.2014.06.100

Applied Surface Science

Volume 323, 30 December 2014, Pages 88-95

https://doi.org/10.1016/j.apsusc.2014.06.100 Get rights and content

Highlights

•
Mo₂C surface can deoxygenate propanal and 1-propanol to produce propene through a similar intermediate (propoxide or η²(C,O)-propanal).
•
Mo₂C surface can deoxygenate furfural and furfuryl alcohol to make 2-methylfuran through a 2-methylfuran-like intermediate.
•
The presence of furan ring modifies the selectivity between deoxygenation and hydrogenation/dehydrogenation pathways.

Abstract

The selective deoxygenation of aldehydes and alcohols without cleaving the C single bond C bond is crucial for upgrading bio-oil and other biomass-derived molecules to useful fuels and chemicals. In this work, propanal, 1-propanol, furfural and furfuryl alcohol were selected as probe molecules to study the deoxygenation of aldehydes and alcohols on molybdenum carbide (Mo₂C) prepared over a Mo(1 1 0) surface. The reaction pathways were investigated using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The deoxygenation of propanal and 1-propanol went through a similar intermediate (propoxide or η²(C,O)-propanal) to produce propene. The deoxygenation of furfural and furfuryl alcohol produced a surface intermediate similar to adsorbed 2-methylfuran. The comparison of these results revealed the promising deoxygenation performance of Mo₂C, as well as the effect of the furan ring on the selective deoxygenation of the C double bond O and C single bond OH bonds.

Introduction

The development of selective catalysts for deoxygenating aldehydes and alcohols has been the subject of many recent investigations of biomass conversion. Aldehydes and alcohols account for up to 25 wt% of bio-oil from fast pyrolysis of raw biomass [1]. These high oxygen contents in bio-oils require deoxygenation before being utilized. The desired deoxygenation catalysts should show high C single bond O bond scission selectivity compared to CC bond scission to retain the carbon chain and to reduce CO/CO₂ production which usually comes along with the traditional decarbonylation/decarboxylation pathway [2]. Due to the complexity of bio-oil, studying small model molecules should be an efficient way of guiding catalyst design. Propanal and 1-propanol are excellent probe molecules due to their simple molecular structure and high vapor pressure which are suitable for collecting mechanistic information by performing surface science studies. Furfural and furfuryl alcohol (Scheme 1) provide opportunities for investigating the effect of furan ring on deoxygenation. In addition, furfural could be produced from hydrolyzing and dehydrating the hemicellulosic part of raw biomass [3], [4]. Selective C1 double bond O1 bond scission of furfural can produce 2-methylfuran, which is a promising biofuel due to its high research blending octane number and high energy density [3].

Direct C double bond O bond scission of propanal was rarely reported on transitional metal surfaces. Decarbonylation to produce CO, H₂ and C₂ hydrocarbons were dominant on Pd(1 1 1) [5], Rh(1 1 1) [6] and Pt(1 1 1) [7]. Acyl and ketene were observed as important intermediates for decarbonylation on surfaces like Pd(1 1 1) [5]. On the other hand, direct C single bond O bond scission of 1-propanol to make C₃ hydrocarbons was reported on Mo(1 1 0) [8].

Transitional metal carbides, especially tungsten carbide (WC) and molybdenum carbide (Mo₂C), are emerging materials with application in heterogeneous catalysis [9], [10], [11] and electrocatalysis [11] due to their unique catalytic properties and low cost compared to precious metals. Recently investigation of small oxygenates on WC and Mo₂C surfaces indicated that these carbide materials could be promising for deoxygenation reactions. For example, the selective C single bond O/C double bond O bond scission to make C₂ hydrocarbons was observed for the reactions of ethanol and glycol aldehyde on WC [12], [13] and Mo₂C surfaces [14], [15]. However, in synthesizing WC and Mo₂C catalyst particles, it was found that WC had a much lower surface area due to higher synthesis temperature required [16] and were less stable in the deoxygenation reactions [17] than Mo₂C. Therefore, the current study was focused on the understanding of deoxygenation pathways of aldehydes and alcohols on Mo₂C using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). HREELS helped identify potential reaction intermediates and provided mechanistic insights into these reactions. Comparison between aldehydes and alcohols revealed whether and how C single bond O and C double bond O bond scission was different on the Mo₂C surface. Comparison between C₃ oxygenates and furans provided useful information on how the presence of the furan group affected the selectivity toward CO/CO bond scission.

Section snippets

Materials preparation

A Mo(1 1 0) single crystal was purchased from Princeton Scientific Corp. with a purity of 99.999%. The crystal was 1.5 mm thick and with a diameter of 12.0 mm. Two tantalum posts were used to hold the Mo(1 1 0) single crystal and served as contacts for resistant heating and liquid nitrogen cooling. A K-type thermocouple was spot welded to the back of the crystal and used to measure the temperature. The temperature of the Mo(1 1 0) crystal can be varied between 90 K and 1150 K. Ne⁺ sputtering and

TPD of propanal and 1-propanol

Fig. 1 displays the TPD spectra after exposing 4 L (1 L = 1 × 10⁻⁶ Torr s) propanal (red spectra) and 4 L 1-propanol (blue spectra) onto Mo₂C at 100 K. The exposure of 4 L corresponds to the near saturation coverage of the first monolayer of adsorbed propanal and 1-propanol. For the reaction of propanal, H₂, 1-propanol and propene were the major gas-phase products. Selective C double bond O bond scission (deoxygenation) was revealed to be a major reaction pathway by the detection of propene, which commenced at 300 K,

Conclusions

In conclusion, the Mo₂C surface selectively deoxygenates propanal and 1-propanol to produce propene. The selective deoxygenation of propanal and 1-propanol proceeds through a similar intermediate (propoxide or η²(C,O)-propanal). The Mo₂C surface also selectively deoxygenates furfural and furfuryl alcohol to make 2-methylfuran through a 2-methylfuran-like intermediate. The presence of the furan ring modifies the selectivity between deoxygenation and hydrogenation/dehydrogenation pathways.

Acknowledgements

This work was supported by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, the U.S. Department of Energy under Award Number DE-SC0001004.

References (31)

L.E. Murillo et al.
Adsorption and reaction of propanal, 2-propenol and 1-propanol on Ni/Pt(1 1 1) bimetallic surfaces
Surf. Sci.
(2008)
A.L. Stottlemyer et al.
Reactions of oxygen-containing molecules on transition metal carbides: surface science insight into potential applications in catalysis and electrocatalysis
Surf. Sci. Rep.
(2012)
A.P. Farkas et al.
Adsorption and reactions of ethanol on Mo₂C/Mo(1 0 0)
Surf. Sci.
(2007)
H.H. Hwu et al.
Reactions of methanol and water over carbide-modified Mo(1 1 0)
Surf. Sci.
(2003)
A.L. Stottlemyer et al.
Reactions of methanol and ethylene glycol on Ni/Pt: bridging the materials gap between single crystal and polycrystalline bimetallic surfaces
Surf. Sci.
(2009)
J.L. Davis et al.
Decarbonylation and decomposition pathways of alcohol's on Pd(1 1 1)
Surf. Sci.
(1987)
J.L. Davis et al.
Spectroscopic identification of alkoxide, aldehyde, and acyl intermediates in alcohol decomposition on Pd(1 1 1)
Surf. Sci.
(1990)
G. Sbrana et al.
Vibrational spectra and isomerism in propyl- and butylaldehydes
J. Mol. Spectrosc.
(1970)
S. Sitthisa et al.
Conversion of furfural and 2-methylpentanal on Pd/SiO₂ and Pd–Cu/SiO₂ catalysts
J. Catal.
(2011)
S. Sitthisa et al.
Selective conversion of furfural to methylfuran over silica-supported NiFe bimetallic catalysts
J. Catal.
(2011)

G.W. Huber et al.

Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering

Chem. Rev.

(2006)

H. Ren et al.

Selective hydrodeoxygenation of biomass-derived oxygenates to unsaturated hydrocarbons using molybdenum carbide catalysts

ChemSusChem

(2013)

J.-P. Lange et al.

Furfural – a promising platform for lignocellulosic biofuels

ChemSusChem

(2012)

S. Dutta et al.

Advances in conversion of hemicellulosic biomass to furfural and upgrading to biofuels

Catal. Sci. Technol.

(2012)

J.L. Davis et al.

Polymerization and decarbonylation reactions of aldehydes on the Pd(1 1 1) surface

J. Am. Chem. Soc.

(1989)

Cited by (44)

Transition metal carbide catalysts for Upgrading lignocellulosic biomass-derived oxygenates: A review of the experimental and computational investigations into structure-property relationships
2023, Catalysis Today
Transition metal carbide (TMC) catalysts, due to their noble metal like characteristics,have emerged as potential candidates for the hydrodeoxygenation (HDO) of biomass derived species, including the pyrolysis product bio-oil. However, the selectivity for deoxygenation, excessive hydrogenation and stability under operating conditions,remain as key challenges. Hence, this paper presents a comprehensive review of the state of the art with regard to (i) the preparation and structure of TMCs, (ii) characterization of active sites on TMCs and (iii) fundamental knowledge of the reaction mechanisms/pathways and associated energetics of HDO of model compounds which are present in biomass derived bio-oil. We believe that this fundamental knowledge will greatly assist researchers to systematically modify the composition and structure of TMCs to optimize their HDO performance.
Thermodynamic analysis and microstructural evolution of the W-Mo-Ni-C system produced by mechanical alloying
2022, Physica B: Condensed Matter
In this research, the microstructural evolution of the W-Mo-Ni-C system was studied by conducting a thermodynamic analysis of formation enthalpies using the Miedema model. Samples were synthetized with different milling times of up to 240 h and analyzed using X-ray diffraction to determine the phases that were produced at each stage of the synthesis. The experimental results indicated carbon diffusion into the transition metal lattice, as WC formation was observed at 120 h and NiC formation was observed at 160 h. Nanostructured MoNi3 and MoW alloys were identified at initial stages from 40 h to 120 h, and as carbon diffusion continued, the MoW alloy transformed into WMoC carbide at 200 h. The Miedema model predictions established that the necessary energy for carbide formation is much larger than that for the formation of alloys of transition metals, demonstrating that these alloys must be formed first, which was validated by experimental data. It was found that the mechanical alloying process produced materials that were out of equilibrium.
Upgrading of benzofuran to hydrocarbons by hydrodeoxygenation over nickel–molybdenum carbide catalysts supported inside multi-wall carbon nanotubes
2022, Fuel Processing Technology
This work proposed a controllable synthesis of Ni-Mo catalyst supported inside multi-wall carbon nanotubes (CNTs). The results indicate that Ni improved the β-Mo₂C formation and markedly promoted the benzofuran (BF) hydrogenation and hydrodeoxygenation activity of the catalysts. The synergistic interaction between Ni and Mo reached the maximum at a Ni/Mo molar ratio of 0.3, which could be favored by the proximity between the Ni and β-Mo₂C particles inside the CNTs reaching a 99.5% of BF conversion to hydrogenated and deoxygenated products as 2,3-dihydrobenzofuran, octahydrobenzofuran, and ethylcyclohexane; in contrast, BF conversion on unsupported Ni-Mo₂C-0.3 was only 0.7%. Deoxygenated products are favored under different conditions, such as the time, and mainly with the temperature achieving 93.8% of yield toward deoxygenated products with 100% of BF conversion at 320 °C. However, the catalyst activity is lost through reuse cycles, likely due to the deposition of high molecular weight compounds (coke) on the catalyst surface.
Transition metal carbides and nitrides as catalysts for thermochemical reactions
2021, Journal of Catalysis
Citation Excerpt :
In brief, carbide films have been synthesized on the surface of parent metal single crystals by undergoing multiple cycles of dosing C2H4 and annealing to substrate-dependent temperatures. For example, Mo2C films have been synthesized on a Mo(1 1 0) surface by two cycles of dosing C2H4 at 600 K and annealing the surface to 1150 K [30], as well as on Mo(1 0 0) by exposing the surface to ethylene at 1200 K [31]. Similarly, WC films have been prepared on W(1 1 1) surfaces by 3 cycles of dosing C2H4 at 90 K and annealing the surface at 1200 K [32], and on W(1 1 0) by heating the surface to 1250 K for 10 min in the presence of dosed C2H4, followed by flash annealing to 1900 K [33].
Transition metal carbides and nitrides (TMCs and TMNs) have attracted much attention due to their unique physical and chemical properties brought by the incorporation of interstitial carbon and nitrogen into the crystal lattice of the parent metals. Recent advances in utilizing TMCs and TMNs have revealed their intriguing catalytic properties in many industrially important reactions, including heteroatom removal, CO₂ activation, alcohol reforming, and water–gas shift reactions. The promising activity, selectivity, and stability of TMCs and TMNs, either as catalysts or as supports for other metals, are often attributed to their strong interactions with the adsorbates, tunable surface properties, as well as the synergy with supported metals. This review summarizes the synthesis and characterization of TMC and TMN model surfaces and powder catalysts, and uses several case studies to demonstrate their unique catalytic properties in these important reactions. A discussion is also provided regarding the challenges and opportunities associated with the utilization of TMCs and TMNs in thermocatalysis.
Enhanced stability of tungsten carbide catalysts via superhydrophobic modification for one-pot conversion of biomass-derived fructose involving water and iodine
2021, Applied Surface Science
Developing cost-effective and high-performance catalysts in biomass chemistry is motivated by creating sustainable technologies dependent on inexpensive and abundant resources. The existing methods for the direct preparation of 5-methylfurfural (5-MF) from biomass-derived fructose mediated by hydrogen iodide (HI) mainly require precious metal catalysts. This research showed that low-cost tungsten carbide (WC) was capable to produce HI from iodine (I₂) via liquid-phase hydrogenation, but a pivotal limitation was the poor stability under the combination effects of water and I₂. To solve this problem, the bulk WC and the high dispersion supported WC were modified by hydrophobic organosilicones through simple liquid phase deposition. Both of the two superhydrophobic WC materials had better stability and their catalytic activity were comparable to the expensive palladium-carbon (Pd/C) catalyst in the preparation of 5-MF, especially the superhydrophobic high dispersion supported WC. This work highlights the potential of the low-cost WC with simple superhydrophobic modification in assisting the direct preparation of 5-MF from fructose mediated by HI, which has high significance to the sustainable development of the low-cost biomass chemical engineering.
A DFT study of methane conversion on Mo-terminated Mo<inf>2</inf>C carbides: Carburization vs C–C coupling
2021, Catalysis Today
Molybdenum carbides have been believed to catalyze C–C coupling to generate aromatics from methane conversion. Herein, a systematic study of methane activation on the Mo-terminated Mo₂C surfaces have been performed using density functional theory calculations. Our results indicate that the Mo-terminated β-Mo₂C surface exhibits a superior activity toward methane activation. Carburization through insertion of carbon atoms into the subsurface interstitial sites of β-Mo₂C reduces the reactivity towards methane activation; and complete carburization in the subsurface layer of β-Mo₂C makes it behave similarly to α-Mo₂C, which has a completely carburized subsurface layer, and α-MoC towards methane conversion. Consequently, dimerization of the CH* adspecies through CC coupling occurs more readily, resulting in C₂H₂*, a potential precursor to produce long chain hydrocarbons or aromatics. This study also demonstrates a dynamic nature of carburization of molybdenum carbides under the condition of methane activation, which is expected to play an important role in determining the activity and selectivity for, e.g., dehydro-aromatization.

View all citing articles on Scopus

View full text

Selective deoxygenation of aldehydes and alcohols on molybdenum carbide (Mo2C) surfaces

Highlights

Abstract

Introduction

Section snippets

Materials preparation

TPD of propanal and 1-propanol

Conclusions

Acknowledgements

Surf. Sci.

Surf. Sci. Rep.

Surf. Sci.

Surf. Sci.

Surf. Sci.

Surf. Sci.

Surf. Sci.

J. Mol. Spectrosc.

J. Catal.

J. Catal.

Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering

Chem. Rev.

Selective hydrodeoxygenation of biomass-derived oxygenates to unsaturated hydrocarbons using molybdenum carbide catalysts

ChemSusChem

Furfural – a promising platform for lignocellulosic biofuels

ChemSusChem

Advances in conversion of hemicellulosic biomass to furfural and upgrading to biofuels

Catal. Sci. Technol.

Polymerization and decarbonylation reactions of aldehydes on the Pd(1 1 1) surface

J. Am. Chem. Soc.

Selective deoxygenation of aldehydes and alcohols on molybdenum carbide (Mo₂C) surfaces