Methanol steam reforming (MSR) catalysts are derived from perovskite-type oxides LaCo 1−x−y Pd x Zn y O 3 ± δ by reductive pretreatment. The unsubstituted LaCoO 3 ± δ (LCO) and LaCo 1−x−y Pd x Zn y O 3 ± δ (Co substituted with Pd and/or Zn) are synthesized by a citrate method and characterized by different techniques. The perovskite-type oxides exhibit a rhombohedral crystal structure and a comparable surface area (≈8.5 ( ± 2) m 2 g −1 ). The temperature-programmed reduction (TPR) shows low (100°C < T < 450°C) and high (T > 450°C) temperature reduction events that correspond to partial and complete reduction of the non-rareearth metal ions, respectively. At high temperatures, Pd-Zn alloy nanoparticles are formed exclusively on Pd-and Zn-containing LaCo 1−x−y Pd x Zn y O 3 ± δ , as evident from high angular annular dark-field scanning transmission electron microscopy (HAADF-STEM). The CO 2 -selective MSR performance of the catalysts strongly depends on the reductive pretreatment temperature, catalyst composition (i.e., the Pd : Zn molar ratio and the degree of Co substitution) and reaction temperature. Only LaCo 1−x−y Pd x Zn y O 3 ± δ catalysts show a low-temperature CO 2 selectivity maximum between 225 and 250°C, while all catalysts present similar high-temperature selectivity maxima at T > 400°C. The former is missing on LCO, LaCo 1−x Pd x O 3 ± δ or LaCo 1−y Zn y O 3 ± δ . Pd-Zn nanoparticles facilitate ZnIJOH) 2 and CoIJOH) 2 formation exclusively on LaCo 1−x−y Pd x Zn y O 3 ± δ , as evident from in situ XRD under steam atmosphere. This indicates the important role of Pd-Zn nanoparticles in the low-temperature CO 2 selectivity, which is improved from 0 to 76% at 225°C on LCO and LaCo 0.75 Pd 0.125 Zn 0.125 O 3 ± δ , respectively. The high-temperature CO 2 selectivity is governed by the bulk catalyst composition and the occurrence of reverse water gas shift reaction.Catal. Sci. Technol. This journal is

The perovskite-type oxides LaCoO 3±d (LCO) with and without substitution of Co by Pd and/or Zn are studied for steam reforming of methanol (SRM). The catalysts LaCo 1-x-y Pd x Zn y O 3±d are synthesized by amorphous citrate method and subjected to calcination at 800°C for 2 h. The catalysts are characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), N 2-physisorption (BET), X-ray diffraction (XRD) and tested in SRM reaction. The surface area of the catalysts is around 9 (±1) m 2 /g. The XRD patterns of the catalysts reflect only rhombohedral crystal structure, indicating the phase purity of the perovskites. The SRM performance of the catalysts, especially the CO 2 selectivity below 275°C, is strongly dependent on the catalyst composition and reaction temperature. The CO 2 selectivity profile of Pd and Zn containing LaCo 0.85 Pd 0.075 Zn 0.075 O 3±d consists of two distinct maxima, one at 225°C and the other above 375°C. The former is missing on un-substituted LCO or mono metal substituted LaCo 0.87 Pd 0.13 O 3±d and LaCo 0.89-Zn 0.11 O 3±d , which is attributed to CO 2 selective phase related to Pd and Zn. The high temperature CO 2 selectivity maximum of the catalysts is not dependent on the Co substitution by Pd and/or Zn and is ascribed, in general, to the bulk catalyst composition.

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1 Introduction Perovskite-type oxides have received a great deal of attention owing to their remarkable physical, chemical, electrical and magnetic properties which find them in a myriad of energy conversion and storage applications such as thermoelectricity, solid-oxide fuel cell electrodes, catalysis and battery materials [1][2][3][4]. The elusive self-regenerative property of the materials has been proposed for LaFe 0.57 Co 0.38 Pd 0.05 O 3 to explain its unprecedented stability under redox atmosphere [5]. However, an electron microscopy study concludes that this property is quite limited in Pd deposited LaFeO 3 thin film on SrTiO 3 [6]. For the first time we provide experimental evidence on the composition dependent self-regenerative property of perovskites that can categorically explain the contradictory observations [5][6][7][8]. The self-regenerative property involves segregation and reintegration of noble metals such as Pd out and into the perovskite crystal lattice under reductive and oxidative atmospheres, respectively [5]. This property greatly suppresses the sintering of noble metal and thereby prevents loss of material properties (i.e., deactivation) for different applications [5,9].

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