Abstract
Bio-oil can be obtained via fast pyrolysis of biomass, and typically contains acetic acid (~30 mass %). The acetic acid has often been tested as a model compound for hydrogen production via reforming bio-oil, in which catalysts are a key factor for stable hydrogen production. However, deactivation of catalysts by coking and oxidation hinders the application of the reforming process. Dolomite-derived Ni-based catalysts with Fe additive, MgNi0.2Ca0.8−xFexO2±δ (x = 0–0.8), were successfully synthesized by the hydrothermal synthesis method, and then tested in auto-thermal reforming (ATR) of acetic acid (AC). The MgNi0.2Ca0.5Fe0.3O2±δ catalyst performed a stable reactivity in ATR: the conversion of AC reached 100%, and the H2 yield remained stable around 2.6 mol-H2/mol-AC. The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, X-ray photoelectron spectra (XPS), H2-temperature-programmed reduction (TPR), inductively coupled plasma- atomic emission spectroscopy (ICP-AES) and Thermogravimetry (TG); the results show that a periclase-like solid solution of Mg(Ni,Fe)O and lime were formed via the precursors of dolomite and hydrotalcite, and then transformed into Fe-rich Ni-Fe alloy with basic support of MgO-CaO after reduction. The stable Ni0 spices with basic support can explain the stability and resistance to coking during ATR of AC.
Highlights
Hydrogen has long been viewed as a clean energy carrier, and can be extracted via reforming of fossil resources, e.g., natural gas or coal
For the iron-free catalyst of MNC0.8 F0.0 (Figure 1a), the AC conversion started near 99.0% and decreased slightly to 97.2% in the end, while the H2 yield was recorded near 2.1 mol-H2 /mol-AC. 1 mol-H2 /mol-AC, as indicated in Table 2 of the average activity data during the auto-thermal reforming (ATR) process
The selectivity to acetone varied near 10.4%, suggesting that part of acetic acid was transformed into acetone via the ketonization route (2CH3 COOHÑCH3 COCH3 + CO2 + H2 O) and the produced acetone has not been converted via reaction of steam reforming (CH3 COCH3 + 5H2 OÑ3CO2 + 8H2 ) [17,18]
Summary
Hydrogen has long been viewed as a clean energy carrier, and can be extracted via reforming of fossil resources, e.g., natural gas or coal. Biomass is an important alternative renewable CO2 -neutral resource for hydrogen production, while bio-oil produced via fast-pyrolysis of biomass is attracting attention for its high energy density and transportation convenience [1,2,3]. Within bio-oil, acetic acid (AC) is one of the major components (~30 mass %), and has often been tested as a model compound for hydrogen production via processes of steam reforming Ni-based catalysts have been widely investigated due to its high catalytic activity for breakage of C–C in the reforming process; on the other hand, acidic sites within the supports of Al2 O3 or ZrO2 favor decomposition and polymerization of AC with derivatives of acetone, ethylene, etc., resulting in carbon deposition [4,8]. Oxides of alkaline earth metals with basic sites, e.g., MgO and CaO, have been used as supports or additives and proved effective to suppress coking over acidic sites [9,10,11]
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