Degradation and regeneration of copper-iron spinel and zeolite composite catalysts in steam reforming of dimethyl ether
Graphical abstract
The catalyst degradation was attributable mainly to the carbon deposition. The regeneration treatment in air at 500–700 °C could not only recover the catalytic performance of the degraded catalysts as compared with the fresh catalyst, but could also improve it.
Introduction
In recent years, steam reforming of dimethyl ether (DME SR) has been regarded as a promising process to produce hydrogen for feeding fuel cell systems. Dimethyl ether (DME) is a suitable fuel because of its high hydrogen-to-carbon ratio in molecules, its high energy density, and its non-toxic and harmless nature. The well-developed infrastructure of liquefied petroleum gas (LPG) can be readily adapted for DME use due to their similar physical properties of the two materials. Among hydrocarbon and oxy-hydrocarbon fuels, DME and methanol (MeOH) can be reformed at relatively lower temperatures of 200–400 °C. Currently, DME is produced commercially from synthetic gas, which is obtained from natural gas, biomass, and coal, by a two-step process via MeOH or by a single-step direct process to DME [1], [2], [3], [4], [5], [6], [7]. Moreover, DME is expected to find applications as a multi-use fuel for turbine and boiler systems, diesel engine systems, and fuel cell systems [8], [9].
The steam reforming of DME (Reaction (1)) consists of two moderately endothermic reactions in sequence: DME hydrolysis (DME HYD) to methanol (Reaction (2)) and methanol steam reforming (MeOH SR) to hydrogen and carbon dioxide (Reaction (3)).DME SR: (CH3)2O + 3H2O → 6H2 + 2CO2 ΔHr0 = 135 kJ mol−1DME HYD: (CH3)2O + H2O → 2CH3OH ΔHr0 = 37 kJ mol−1MeOH SR: CH3OH + H2O → 3H2 + CO2 ΔHr0 = 49 kJ mol−1
Thus, a bifunctional catalyst consisting of an acid function (various solid-acids such as zeolite and alumina were proposed as DME HYD catalysts) and a metallic function (Cu-, Pt-, or Pd-based catalysts as MeOH SR catalysts) is generally needed for overall DME SR. Several research groups have studied DME SR processes employing a number of Cu-based catalyst systems, such as 12-tungstosilicoheteropolyacid/γ-Al2O3-Cu/SiO2 [10], Cu-Zn/Al2O3 prepared by sol–gel method [11], H-mordenite-Cu/CeO2 [12], WO3/ZrO2-Cu/CeO2 [13], [14], Cu/GaXAl10−XO15 [15], [16], and various zeolites coupled with Cu/ZnO/Al2O3 catalysts [17], [18], [19], [20]. It was reported that MFI (ZSM-5), H-mordenite, zeolite Y, and WO3/ZrO2 exhibited a high hydrolysis activity due to their strong acid sites; however, a significant degradation has also been observed. Among weakly acidic catalysts, γ-Al2O3 has been considered as a DME HYD catalyst that offers a high durability without unwanted side-reactions. It is known that the high reaction temperature above 300 °C is generally required for effective DME HYD reaction over γ-Al2O3. The reaction temperatures close to 400 °C inevitably give rise to severe sintering of Cu species and the lower reformate quality, namely, high formation of CO and CH4. The zeolite-based composite has, therefore, been attractive when used in a low reforming temperature range.
In the previous work, we have reported a comparative study of the catalytic performance and the kinetic parameter of various solid-acid catalysts in DME HYD [21]. Although solid-acid catalysts with strong acidity and large acid amounts resulted in higher conversion in DME HYD, fast degradation due to coking and low quality of product were observed with increasing acidity and acid amount. In the DME SR over the Cu-based spinels mixed with various solid-acids catalysts, alumina composite catalysts are superior to zeolite composite ones with regard to durability. Some research groups have reported the high stability of the zeolite-based composite catalysts for DME SR [17], [20]. Among various types of zeolite, ZSM-5 type is one of the most promising catalysts for DME HYD. To the best of our knowledge, a clear understanding about the degradation and regeneration behaviors over the ZSM-5 coupled with Cu-Fe spinel catalyst has not been attained so far. Thus, in this work, the degradation behavior of the MFI-type zeolite (ZSM-5) and Cu-Fe spinel composite catalyst for DME SR was systematically studied in various reaction conditions. The regeneration procedure of the degraded catalysts was also investigated.
Section snippets
Catalyst preparation and characterization
Copper-iron spinel CuFe2O4 was prepared by the sol–gel method from a citrate complex precursor [22]. An aqueous solution of Cu and Fe nitrates was stirred at 60 °C for 2 h, followed by addition of citric acid. The molar ratio of the total metal cations to citric acid was 1.5. The solution was kept at 60 °C for 1 h, and then heated to 90 °C to evaporate the water. The precipitate obtained was heated at 140–350 °C until the oxide powder was formed. The resultant powder was calcined in air at 900 °C for
Catalytic activity of CuFe2O4 mixed with ZSM-5 or γ-Al2O3 catalysts
The catalytic activity for DME SR was evaluated over the composite catalysts of CuFe2O4 spinel mixed with ZSM-5 (CuFe2O4/ZSM-5) or γ-Al2O3 (CuFe2O4/Al2O3). The weight ratio of CuFe2O4 to solid-acid was 2 to 1. As depicted in Fig. 1, CuFe2O4/ZSM-5 exhibited higher DME conversion than CuFe2O4/Al2O3 throughout the temperature range examined. It was considered that ZSM-5 is fairly active for DME HYD, leading to the high conversion of DME in DME SR over the composite catalyst. Above 300 °C, a
Conclusions
The degradation and regeneration behaviors of the composite catalyst of CuFe2O4 spinel and ZSM-5 in DME SR have been studied. The degradation of the catalyst could be suppressed in the conditions of high steam/DME and high weight/flow ratio, high composite weight ratio of CuFe2O4/ZSM-5, and low reaction temperature for DME SR reaction. The degraded catalyst was fully regenerated by the heat treatment in air atmosphere. Furthermore, the regeneration treatment at 500–700 °C improved the catalytic
References (27)
- et al.
Appl. Catal. A: Gen.
(2000) - et al.
Thermochim. Acta
(2005) - et al.
Appl. Catal. A: Gen.
(2006) - et al.
Fuel Process. Technol.
(2008) - et al.
J. Power Sources
(2006) - et al.
Fuel
(2008) - et al.
Appl. Catal. A: Gen.
(2001) - et al.
Appl. Catal. A: Gen.
(2004) - et al.
Appl. Catal. A: Gen.
(2004) - et al.
Appl. Catal. A: Gen.
(2006)
Appl. Catal. A: Gen.
Appl. Catal. A: Gen.
Appl. Surf. Sci.
Cited by (37)
Dimethyl ether as circular hydrogen carrier: Catalytic aspects of hydrogenation/dehydrogenation steps
2021, Journal of Energy ChemistryCitation Excerpt :In this review, the catalytic aspects of SRD are discussed, at the light of results published since 2000. The catalytic performances of some of the catalytic systems discussed in this paper [102–145] are summarized in Table 3. In 2001, Sobyanin et al. experimentally confirmed, for the first time, the potentiality of SRD as an attractive method for on-board hydrogen production [102].
Insights into the long-term stability of the magnesia modified H-ZSM-5 as an efficient solid acid for steam reforming of dimethyl ether
2019, International Journal of Hydrogen EnergyCitation Excerpt :To confirm this, the used bifunctional catalysts after a TOS of 50 h were characterized. The coking is inevitable during SRD, and is studied as the main reason for the deactivation of the zeolite-based bifunctional catalysts [13,35–38,40,49]. Thus, the bifunctional catalyst after SRD for 50 h was applied to XPS analyses, and the C 1s core-level spectra are given in Fig. S1 (Supplementary Material).
Evaluation of regenerative function and activity of reforming toluene by composite catalyst containing spinel oxide
2019, International Journal of Hydrogen EnergySpinel-based oxide cathode used for high temperature CO<inf>2</inf>/H<inf>2</inf>O co-electrolysis
2019, Solid State IonicsCitation Excerpt :It is worth noting that the operated cell was flowed with inert Ar gas during the cooling process in order to preserve the state in operation as much as possible. Additionally their further studies also confirmed that the phenomena of phase separation can be recovered by a re-heating process at 900 °C in air, leading to the regeneration of the pure phase of CuFe2O4 [19]. More recently, other studies have also reported that CuO can be a good catalyst for CO2 reduction, and has good activity for reforming of hydrocarbons (e.g. CH4) [20,21].
NiAl<inf>2</inf>O<inf>4</inf> spinel-type catalysts for deoxygenation of palm oil to green diesel
2018, Chemical Engineering Journal
- 1
Present address: National Nanotechnology Center, National Science and Technology Development Agency, 111 Thailand Science Park, Paholyothin Rd., Patumthani 12120, Thailand.
- 2
Present address: Department of Chemical System Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.