New Active and Selective Rh−REO_x−Al₂O₃Catalysts for Ethanol Steam Reforming

Abstract

The effect of the addition of a wide range of rare earth elements (Sc, Y, La, Er and Gd) on the catalytic behavior of Rh/Al 2 O 3 base catalyst in the ethanol steam reforming (ESR) reaction was investigated. Physical-chemical properties of Rh-REO x -Al 2 O 3 materials have been evaluated by H 2 chemisorption, XRD, BET, TPR, IR spectroscopy and TPO. It was established that the catalytic behavior of the Rh/Al 2 O 3 base catalyst is widely improved by the promotion with rare earth (RE) elements. It has been shown that the RE elements do not have an important impact on the oxidation state and the dispersion of the metallic centers but greatly alter the acid-base properties of the support. It was demonstrated that the catalytic performances of Rh-REO x -Al 2 O 3 catalysts are mainly due to the increase of the support basicity and to the rearrangement of acid sites. The presence of a new type of Lewis acid sites (LAS) of weak strength on Rh-REO x -Al 2 O 3 materials leads to decrease the production of coke precursor (C 2 H 4 ). Finally, the most basic support leads to the highest hydrogen yield and to the less stable coke.

Ethanol steam reforming over Pt/Al 2 O 3 and Rh/Al 2 O 3 catalysts: The effect of impurities on selectivity and catalyst deactivation

“…acetaldehyde, are not shown.) 26 As we have outlined previously this underestimates the hydrogen yield as it takes no account of hydrogen produced during carbon laydown [17][18][19]. Nevertheless it does give a correct carbon and oxygen balance.…”

Enhanced oxygen mobility and reactivity for ethanol steam reforming

“…3 Increasing interests in developing hydrogen fuel cells spur investigations on understanding physicochemical properties of ethanol steam reforming (ESR) catalysts. The ESR catalysts mainly include supported base-metals (e.g., Ni, Co, Cu) [4][5][6][7] and supported noble metals (e.g., Pt, Rh, Ru, Pd, and Ir) [8][9][10][11] . Although noble metal-based catalysts show outstanding activity and stability in ESR, 12,13 their largescale application is limited primarily due to the high cost.…”

Design of Nanocatalysts for Green Hydrogen Production from Bioethanol

“…[55][56][57] The addition of rare-earth oxides to alumina can also orientate the reaction and improve hydrogen production. [58] Finally, the support can help the metal to oxidise coke deposits. Autothermal steam reforming may provide the oxygen required for coke oxidation.…”

“…The main drawback of the g-alumina support for bioethanol steam reforming is its acidity, which favours coke deposition, especially in the presence of impurities such as higher alcohols. This acidity may be decreased by adding basic species such as alkaline, alkaline earth [58,71,72] or rare earth [31,58] oxides. However, supports that have been demonstrated to lead to stable catalysts for ESR are not necessarily suitable for crude bioethanol steam reforming.…”

“…Thus, a Rh/MgAl 2 O 4 catalyst was rapidly deactivated during crude bioethanol steam reforming. With the aim of improving the resistance to coke deposition, and to rationalise the effect of the addition of basic promoters, Can et al [58] added 5 % rare earth (RE) elements to alumina, namely, scandium, yttrium, lanthanum, erbium and gadolinium, by impregnation of the corresponding nitrate followed by calcination at 700 8C to form Sc-Al, Y-Al, La-Al, Er-Al and Gd-Al. The acidity and basicity of the supports were characterised by performing adsorption and thermodesorption experiments of pyridine and CO 2 , respectively, followed by FTIR spectroscopy.…”