Albert Gonche Machoke

Micro/Macroporous System: MFI‐Type Zeolite Crystals with Embedded Macropores

Zeolite crystals with an embedded and interconnected macropore system are prepared by using mesoporous silica particles as a silica source and as a sacrificial macroporogen. These novel hierarchical zeolite crystals are expected to reduce diffusion limitations in all zeolite-catalyzed reactions, especially in the transformation of larger molecules like in the catalytic cracking of polymers and the conversion of biomass.

Nanostructured Encapsulated Catalysts for Combination of Fischer–Tropsch Synthesis and Hydroprocessing

Controlling the selectivity of Fischer–Tropsch synthesis in a single reaction step is highly desirable, but is a major challenge in heterogeneous catalysis. One approach is the application of bifunctional catalysts. However, to control the catalytic properties the morphology of the catalyst needs to be controlled on the nanoscopic scale. Herein, an innovative synthetic approach that allows the bottom‐up construction of nanostructured bifunctional catalysts in a step‐wise manner is described. The resulting material, which exhibits cobalt nanoparticles encapsulated inside a zeolite matrix, was proven to be active in the combined Fischer–Tropsch and cracking reaction, evidenced by a shift from waxy to liquid products. Consequently, the use of this novel approach was demonstrated in terms of material synthesis and catalytic applications.

Chapter 4:Hierarchical Zeolites

Hierarchy is a property of natural and technical systems. Nowadays even zeolite-containing systems make use of property hierarchy in transport related applications. Thus, this chapter provides an overview of zeolite-containing hierarchical materials based on their underlying preparation strategies and pore structure. Starting from an attempt to classify the so-called all-zeolitic systems, the contribution bridges and discusses general preparation pathways of hierarchically organized zeolites and characterization methods specially focused on the property ‘hierarchy’ in zeolite based materials. The different preparation pathways classified into bottom-up and top-down approaches are described and discussed as ‘toolboxes’ to design zeolite-containing materials with tailored porosity. In addition, as the second group of zeolite-containing hierarchical materials, the formation principles and the characteristics of zeolitic composites are discussed as an elementary necessity for their technical use. Finally, the potentially applicable and the already technically used hierarchical zeolites are summarized.

Densification of Silica Spheres: A New Pathway to Nano-dimensioned Zeolite based Catalysts

Nanosized materials are expected to play a unique role in the development of future catalytic processes. Herein, pre-prepared and geometrically well-defined amorphous silica spheres are densified into silica-rich zeolites with nanosized dimensions. After the densification, the obtained nanosized zeolites exhibit the same spherical morphology like the starting precursor but characterized by a drastically reduced size, higher density, and high crystallinity. The phase transformation into crystalline zeolite material and the densification effect are achieved through a well-controlled steam-assisted treatment of the larger precursor particles so that the transformation process proceeds always towards the center of the spheres, just like a shrinking process. Furthermore, this procedure is applicable also to commercially available silica particles, as well as aluminum-containing systems (precursors) leading to acidic nano-catalysts with improved catalytic performance.