Kinetic Parameters for the Selective Hydrogenation of Acetylene on GaPd<sub>2</sub>and GaPd
作者:René R. Zimmermann、Tobias Hahn、Wladimir Reschetilowski、Marc Armbrüster
DOI:10.1002/cphc.201700535
日期:2017.9.20
stable catalyst for the semi‐hydrogenation of acetylene. Knowledge of the underlying reaction kinetics is essential to gain a deeper understanding of the selective hydrogenation on this catalytic material. To date, there has been no experimental kinetic data published for this reaction on a well‐defined intermetallic catalyst possessing isolated active sites. Kineticmeasurements are performed at 140–200 °C
金属间化合物GaPd 2是乙炔半加氢的高度选择性和稳定的催化剂。为了更深入地了解这种催化材料上的选择性加氢,基本的反应动力学知识是必不可少的。迄今为止,尚未发表关于具有分离的活性位点的定义明确的金属间催化剂的该反应的实验动力学数据。动力学测量在140–200°C下进行,发现表观活化能为29(2)kJ mol -1。砷化镓2示出的是第一二元催化剂材料,其在200°C下相对于乙炔显示正反应级(0.89)。乙炔转化率,比活度和对乙烯,乙烷和高级烃的选择性的影响是通过按照实验方法设计的2 4阶乘实验确定的。温度和压力对这些值的影响最大。结果允许实现高乙烯收率的最佳操作。将GaPd 2的反应动力学与获得的GaPd实验结果进行比较,可以发现H 2和C 2 H 2在两种化合物上的反应顺序不同。
Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylenePart I: Preparation and structural investigation under reaction conditions
The intermetallic compounds PdGa and Pd3Ga7 are introduced as selective catalysts for the hydrogenation of acetylene. Single phase PdGa and Pd3Ga7 can readily be prepared by the appropriate thermal treatment of the stoichiometric mixtures of the corresponding elements. The initial low surface areas of the as-prepared materials can be increased by careful mechanical treatment without decomposition.
引入金属间化合物PdGa和Pd 3 Ga 7作为用于乙炔氢化的选择性催化剂。单相PdGa和Pd 3 Ga 7可以通过对相应元素的化学计量混合物进行适当的热处理而容易地制备。可以通过仔细的机械处理而不分解来增加所制备材料的初始低表面积。DSC / TG,原位粉末X射线衍射和原位对PdGa和Pd 3 Ga 7的详细研究在各种惰性或反应性气体气氛下进行热处理时,X射线吸收光谱显示出很高的热稳定性。直至约600 K的温度,晶体结构中的长程和短程有序保持不变。相变和分解都无法检测到。除了较高的热稳定性(在反应条件下保持活性部位隔离)外,在还原条件下未观察到氢或碳在金属间化合物中的结合。除了是有趣的模型系统之外,钯-镓金属间化合物还有望用作高选择性加氢催化剂。
The direct synthesis of hydrogen peroxide from H<sub>2</sub> and O<sub>2</sub> using Pd–Ga and Pd–In catalysts
作者:Sheng Wang、Richard J. Lewis、Dmitry E. Doronkin、David J. Morgan、Jan-Dierk Grunwaldt、Graham J. Hutchings、Silke Behrens
DOI:10.1039/c9cy02210d
日期:——
The direct synthesis of hydrogen peroxide is investigated using PdGa/TiO2 and PdIn/TiO2 catalysts prepared by an acid-washed sol-immobilisation procedure, which allows for enhanced catalytic selectivity.
A two-step synthesis for the preparation of single-phase and nanoparticulate GaPd and GaPd2 by coreduction of ionic metal-precursors with LiHBEt3 in THF without additional stabilizers is described. The coreduction leads initially to the formation of Pd nanop articles followed by a Pd-mediated reduction of Ga3+ on their surfaces, requiring an additional annealing step. The majority of the intermetallic particles have diameters of 3 and 7 nm for GaPd and GaPd2, respectively, and unexpected narrow size distributions as determined by disk centrifuge measurements. The nanoparticles have been characterized by XRD, TEM, and chemical analysis to ensure the formation of the intermetallic compounds. Unsupported nanoparticles possess high catalytic activity while maintaining the excellent selectivity of the ground bulk materials in the semihydrogenation of acetylene. The activity could be further increased by depositing the particles on alpha-Al2O3.
Etching of the intermetallic compounds PdGa and Pd3Ga7: An effective way to increase catalytic activity?
The structurally ordered intermetallic compounds PdGa and Pd3Ga7 constitute highly selective catalysts for the selective semi-hydrogenation of acetylene. The milling of as-synthesized samples, followed by etching with ammonia solution increased the activity of the catalysts by factor of 60. Chemically etched samples possess high activity and simultaneously keep their high selectivity. Chemical analysis confirms that the etching procedure is mostly specific to gallium species, thus less affecting the palladium. Detailed investigations reveal the influence of the chemical etching on the morphology and surface of the particles. As a result of the etching, nano-caverns are formed (SEM and BET), and the surface is enriched in palladium (XPS and EDX), while the bulk crystal structure is not affected (XRD). The mechanism and applicability of the etching procedure is discussed in view of the active-site isolation concept. (C) 2009 Elsevier Inc. All rights reserved.