Influence of the Zn–Al binary oxide composition on the physicochemical and catalytic properties of Ni catalysts in the oxy-steam reforming of methanol

Reac Kinet Mech Cat (2017) 121:453–472 DOI 10.1007/s11144-017-1168-0 Influence of the Zn–Al binary oxide composition on the physicochemical and catalytic properties of Ni catalysts in the oxy-steam reforming of methanol Paweł Mierczynski1 • Magdalena Mosinska1 • Mateusz Zakrzewski1 • Bartosz Dawid1 • Radoslaw Ciesielski1 • Waldemar Maniukiewicz1 • Tomasz Maniecki1 Received: 30 November 2016 / Accepted: 25 February 2017 / Published online: 10 March 2017 Ó The Author(s) 2017. This article is published with open access at Springerlink.com Abstract This paper presents the catalytic properties of mono- and bimetallic nickel supported catalysts in the oxy-steam reforming of methanol. The physicochemical properties of the supported catalysts were studied by various techniques such as TPR, TPD-NH3, XRD and BET. A significant impact of palladium and the support composition on the activity and selectivity of nickel catalysts in OSRM was demonstrated. The highest activity in the oxy-steam reforming of methanol reaction among all nickel catalysts was shown by the 20% Ni/ZnOAl2O3 (Zn:Al = 1:1) catalyst. The acidity results correlate well with the reactivity of the investigated catalysts. The most active monometallic system showed the highest total acidity and was the easiest to reduce compared to the rest of the investigated Ni catalysts. The effect of palladium on the reducibility and reactivity of the nickel supported catalyst was proven. The activity results carried out in the OSRM reaction showed that such catalytic material may be potentially applied in fuel cell technology. Keywords Hydrogen production  Oxy-steam reforming of methanol  ZnOAl2O3  binary oxide  Nickel catalysts  Palladium, bimetallic catalysts Introduction The use of fossil fuels has a negative impact on the environment, causing the emission of harmful oxides into the atmosphere. The emission of harmful gases into the atmosphere is responsible for the formation of smog and the greenhouse effect [1], which presents a serious risk to the human health. In addition, sources of fossil fuels are non-renewable. Their continued exploitation may lead to the depletion of & Paweł Mierczynski ; 1 Institute of General and Ecological Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland 123 454 Reac Kinet Mech Cat (2017) 121:453–472 their sources. Nowadays, the challenge is to obtain energy from renewable sources. One of the possible alternatives to fossil fuels is hydrogen [2]. It can be a fuel of the future because it is an eco-environmentally friendly source of energy. Hydrogen combustion generates large amounts of heat and the only product of this process is water vapor. It is worth emphasizing that the sources of hydrogen are practically inexhaustible. Therefore, the hydrogen production is one of the most promising technologies to generate energy. One of the most promising sources of hydrogen is methanol. It is a good raw material for hydrogen production because it is easily decomposed, which leads to the formation of a hydrogen-rich mixture. Despite the high toxicity, corrosivity and destructive impact on the plastics, methanol has many advantages. It is the simplest alcohol, which has only one carbon in the molecule and is characterized by high hydrogen to carbon ratio. All of these properties indicate, that the oxy-steam reforming of methanol process can be potentially applied to hydrogen production at low temperature (180–330 °C), without a carbon deposit formation [3–6]. The OSRM is a combination of two processes, namely steam reforming and partial oxidation of methanol. It is an energetically favorable process because this reaction runs in the auto-thermal way, without the need to supply any external heat [7–10]. The literature review showed that typical catalytic system using in the oxy-steam reforming of methanol reaction are monometallic: Ni [10–13], Cu [5, 14, 15], Co, Fe, Pd [16, 17], Pt, Ru, Ir, Ag, Au and bimetallic: M–CuO/ZnO/Al2O3, where M = Pt, Pd, Rh, Ru [18, 19] supported catalysts. Furthermore, nickel supported catalysts are widely used in many other processes such as oil refining, hydrocracking, hydrogenation or reforming of hydrocarbons. The active phase of these catalysts is typically metallic nickel supported on various oxides such as c-Al2O3, a-Al2O3, SiO2, ZrO2, ZnO and CeO2. It is also well known that the Ni/Al2O3 system is very active in the steam reforming reaction of various compounds. Additionally, it is well documented in the literature data that nickel supported catalysts have a high efficiency, good structural and thermal stability compared to the noble metal based catalysts [20, 21]. All of the above mentioned suggestions indicate that hydrogen production via the oxy-steam reforming of methanol reaction is a very important topic nowadays. Therefore, the main goal of this work was to evaluate the effect of support composition on the catalytic and physicochemical properties of the nickel supported catalysts in OSRM reaction. Another important aim of the work was to study the impact of palladium on reactivity of nickel catalysts in OSRM process. In order to achieve the intended purposes of the work we prepared mono-Ni and bimetallic Pd– Ni catalysts supported on various binary oxides and tested their reactivity in OSRM reaction. 123 Reac Kinet Mech Cat (2017) 121:453–472 455 Experimental Preparation of the catalytic systems Supports material Binary oxide ZnOAl2O3 (Zn:Al = 2:1, 1:1, 1:2, 1:4) systems were prepared by coprecipitation method. In order to prepare binary oxides with the various molar ratio of Zn:Al = 2:1, 1:1, 1:2, 1:4, the aqueous solutions of zinc nitrate (1 mol/L) and aluminum nitrate (1 mol/L) have been mixed in an appropriate amount with constant stirring at a temperature of 80 °C. Then, in the next step of the synthesis of the supports, a concentrated ammonia solution was added into a mixture until the pH of the solution reached a value between 10 and 11. Thereafter, the solution was stirred for 30 min. In the next step, the resulting precipitate was washed with deionized water. A purified precipitate was firstly dried at 120 °C for 15 h and calcined in air atmosphere for 4 h at 400 °C. Preparation of monometallic and bimetallic catalysts Monometallic nickel catalysts supported on various supports ZnOAl2O3 (Zn:Al = 2:1, 1:1, 1:2, 1:4) were prepared by the wet aqueous impregnation method. A nickel nitrate (V) was used as a precursor of NiO phase. Then the prepared catalysts were dried for 2 h in air atmosphere at 120 °C and finally calcined for 4 h at the same atmosphere at 400 °C. Bimetallic supported catalysts were prepared by a subsequent impregnation method. The palladium phase was introduced on the surface of the monometallic nickel catalyst from palladium nitrate (V) solution. In the next step, the obtained catalysts were dried for 2 h in air at 120 °C, and afterwards they were calcined for 4 h at 400 °C also in air. (...truncated)