Steam reforming of ethanol for hydrogen production over MgO—supported Ni-based catalysts

doi:10.1016/j.apcata.2015.11.020

Applied Catalysis A: General

Volume 518, 25 May 2016, Pages 115-128

https://doi.org/10.1016/j.apcata.2015.11.020 Get rights and content

Highlights

•
The preparation method of MgO significantly affected basicity and reducibility.
•
The basicity followed the order: Ni/MgOpa > Ni/MgOp > Ni/MgOd.
•
The distribution of NiO particles and NiO–MgO solid solution depended on the synthesis conditions.
•
Catalyst deactivation during SR of ethanol was mainly due to carbon deposition.
•
The amount of carbon deposited decreased when the basicity increased.

Abstract

This work studied the effect of preparation method of MgO on the performance of Ni/MgO catalysts for steam reforming of ethanol. Three different MgO were prepared by precipitation and aging, precipitation and decomposition of precursor salt. Depending on the synthesis conditions, the basicity and the type of Ni species significantly varied. TPD of adsorbed CO₂ showed that the MgO prepared by precipitation and aging possess the highest amount of basic sites. TPR and XANES revealed the presence of two different Ni species: NiO particles and Ni²⁺ inserted in the lattice of a NiO–MgO solid solution, which is hardly reducible. Ni supported on MgO obtained by precipitation and aging exhibited the highest reduction degree. The preparation method of MgO also affected the amount of carbon formed during SR of ethanol at 773 K under H₂O/ethanol molar ratio of 3.0. Increasing basicity decreased the amount of carbon deposits, which was attributed to the increase of carbon gasification rate.

Graphical abstract

Introduction

Today, the majority of hydrogen is produced in refineries to upgrade crude oil (hydrocracking and hydrotreating process), in the petrochemical industry to synthesize different chemical compounds (such as ammonia and methanol), for oil and fat hydrogenation and, in metallurgical processes (as a reduction gas) [1]. However, the rising concern with the reduction of greenhouse gas emissions and atmospheric pollution increased the interest in using hydrogen as an energy carrier for power generation with fuel cells as well as for the conversion of biomass into liquid fuels.

Hydrogen can be electrochemically converted in PEM fuel cells to produce electricity for use in transportation applications and portable power devices and also for residential combined heat and power systems [2]. Hydrogen is also required in the hydrodeoxygenation (HDO) process of bio-oil produced from the fast pyrolysis of biomass for gasoline and diesel production [3] as well as in HDO of fermentation products obtained in a sugarcane biorefinery for jet fuel and lubricants production [4].

Hydrogen can be produced through the steam reforming of biomass-derived liquids such as bioethanol, a water and ethanol mixture that may be obtained by biomass fermentation [5], [6], [7], [8]. The steam reforming of ethanol is an attractive route to hydrogen production because: (i) it is a renewable and CO₂-neutral source that can readily be obtained from biomass fermentation; (ii) ethanol is significantly less toxic than methanol and gasoline; (iii) the infrastructure required for ethanol production and distribution is already established in countries like Brazil and USA since ethanol is currently distributed and blended with gasoline.

Different technologies may be applied to generate hydrogen from ethanol, including steam reforming (SR) (Eq. (1)), partial oxidation (POX) (Eq. (2)), and oxidative steam reforming (OSR) (Eq. (3)) [8]:C₂H₅OH + 3H₂O → 2CO₂ + 6H₂C₂H₅OH + 1.5 O₂ → 2CO₂ + 3H₂C₂H₅OH + (3 − 2x) H₂O + xO₂ → 2CO₂ + (6 − 2x)H₂0 < x < 0.5

However, various reaction pathways may occur depending on the reaction conditions and the choice of the catalyst. Some of these reactions lead to the formation of coke and, consequently, induce catalyst deactivation.

The type of support directly influences the product distribution and catalyst stability during ethanol conversion reactions since it also exhibits activity for this reaction. Al₂O₃ is generally used as a support but its acid sites promote the dehydration of ethanol to ethylene, which is considered a precursor of coke [9]. MgO contains strong basic sites, which are proposed to be highly active for ethanol dehydrogenation to acetaldehyde that is considered the primary intermediate of SR of ethanol [9]. It is well known that basic metal oxides minimize carbon formation increasing adsorption of water and promoting the rate of carbon gasification reaction [10]. Therefore, there are many studies in the literature about the SR of ethanol over MgO supported catalysts [9], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. However, carbon formation is still observed for SR of ethanol over Ni/MgO catalysts [11], [12], [13], [14], [15], [18], [19], [20]. In fact, there is no work in the literature that studies the influence of the basic properties of magnesia on the rate of carbon formation during SR of ethanol. Then, the design of a catalyst resistant to carbon formation for SR of ethanol requires a better understanding of the effect of the surface basic properties of magnesia on catalyst deactivation. This can be done by tailoring the surface basic properties of magnesia and, consequently, the amount and strength of basic sites, by controlling the synthesis method. Menezes et al. [21] studied the effect of the preparation method on the surface basicity of MgO. Different MgO were synthesized by precipitation and hydrothermal treatments and decomposition of magnesium nitrate. The samples presented different basic site distributions, revealing the important role of the preparation conditions on tuning the surface basicity.

Therefore, the aim of this work is to study the effect of preparation method of MgO on the performance of Ni/MgO catalysts during ethanol conversion reactions. MgO was prepared by precipitation, precipitation with aging and decomposition of the precursor salt in order to vary the surface basicity. A correlation was established between the density of basic sites and the catalyst resistance to carbon deposition.

Section snippets

Catalyst preparation

The MgOpa sample was prepared by precipitation followed by aging. Mg(NO₃)₂·6H₂O and NaOH solutions were slowly added to a Na₂CO₃ solution under vigorous stirring. The precipitate formed was aged at pH 10 for 12 h. The gel was centrifuged and extensively washed with distilled water until constant pH. Then, it was dried at 373 K for 12 h and calcined at a heating rate of 5 K/min up to 773 K for 5 h.

Another sample (MgOp) was also synthesized by precipitation from the same Mg(NO₃)₂·6H₂O and Na₂CO₃

Catalyst characterization

Table 1 presents the NiO (Ni⁰ in parentheses) and MgO content of all samples. The Ni loading obtained by XRF analysis was close to the nominal value for all samples studied (5.0 wt.% Ni). Furthermore, traces of sodium were not detected.

Fig. 1 shows the XRD patterns of the supports prepared by different methods. The diffractograms of all samples exhibited the diffraction lines characteristic of the periclase MgO phase with cubic structure (PDF#45-0946). However, sharper lines were registered for

Conclusions

Ni supported on MgO catalysts were prepared by three different synthesis routes: precipitation followed by aging; precipitation and decomposition of the precursor salt. The preparation method of MgO significantly affected the total amount of basic sites and the reducibility of the sample. TPD of adsorbed CO₂ showed that the basicity followed the order: Ni/MgOpa > Ni/MgOp > Ni/MgOd. TPR profiles revealed the presence of NiO particles and a NiO–MgO solid solution, which was identified by XRD. The

Acknowledgements

Gleiciele W. Tozzi and Raimundo C. Rabelo-Neto acknowledge the scholarships received from CAPES and FAPERJ. The group thanks LNLS for the assigned beamtime at XAFS-2 (proposal—16244) and XPD (proposal—17955) and for the valuable support to perform the XAFS studies.

References (47)

R. Ramachandran et al.
Int. J. Hydrog. Energy
(1998)
P.D. Vaidya et al.
Chem. Eng. J.
(2006)
M. Ni et al.
Int. J. Hydrog. Energy
(2007)
D.K. Liguras et al.
Appl. Catal. B
(2003)
D.L. Trimm
Catal. Today
(1999)
F. Frusteri et al.
Catal. Commun.
(2004)
F. Frusteri et al.
Int. J. Hydrog. Energy
(2006)
F. Frusteri et al.
J. Power Sources
(2007)
M.S. Batista et al.
J. Power Sources
(2003)
J. Llorca et al.
J. Catal.
(2002)

S. Cavallaro et al.

J. Power Sources

(2001)

F. Frusteri et al.

Appl. Catal. A

(2004)

N. Palmeri et al.

Int. J. Hydrog. Energy

(2007)

Q. Shi et al.

J. Rare Earths

(2009)

E. Ruckenstein et al.

Appl. Catal. A

(1997)

V.K. Díez et al.

J. Catal.

(2006)

M. Nurunnabi et al.

Appl. Catal. A

(2005)

Y.G. Chen et al.

J. Catal.

(1999)

D. Li et al.

Appl. Catal. B

(2011)

O. Yamazaki et al.

Appl. Catal. A

(1996)

J. Li et al.

Chin. J. Catal.

(2009)

S.D. Robertson et al.

J. Catal.

(1975)

B. Scheffer et al.

Appl. Catal.

(1989)

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Steam reforming of ethanol for hydrogen production over MgO—supported Ni-based catalysts

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Catalyst preparation

Catalyst characterization

Conclusions

Acknowledgements

Int. J. Hydrog. Energy

Chem. Eng. J.

Int. J. Hydrog. Energy

Appl. Catal. B

Catal. Today

Catal. Commun.

Int. J. Hydrog. Energy

J. Power Sources

J. Power Sources

J. Catal.

J. Power Sources

Appl. Catal. A

Int. J. Hydrog. Energy

J. Rare Earths

Appl. Catal. A

J. Catal.

Appl. Catal. A

J. Catal.

Appl. Catal. B

Appl. Catal. A

Chin. J. Catal.

J. Catal.

Appl. Catal.