CATEGORY: ZEOLITES
23rd North American Catalysis Society Meeting,
June 2-7, 2013, Louisville, Kentucky
Nanoscale 3D Imaging and Quantification of
Pt/Zeolite Y Hydrocracking Catalysts
Jovana Zečević
k.p.dejong@uu.nl
1 Inorganic Chemistry and Catalysis,Utrecht University, Utrecht (The
Netherlands) 1, Heiner Friedrich2, Petra E. de Jongh1 and Krijn P. de Jong1*
2 Materials and Interface Chemistry, Eindhoven University of Technology,
Eindhoven (The Netherlands)
Introduction
A
wide range of important industrial processes rely heavily on supported metal
catalysts, such as bi-functional zeolite supported Pt catalyst used in oil
refineries for hydrocracking and hydroisomerisation. Assessing particle size
distribution and their location within zeolite support is crucial for
understanding the reaction mechanisms as well as for improving catalyst design.
Commonly used bulk techniques, such as EXAFS, NMR, H2-chemisorption provide
only the average size of Pt particles, while TEM is the most direct technique
which enables visualization of Pt particles and manual measurement which is
often biased, labor intensive and susceptible to errors. Therefore, authors
used electron tomography (3D-TEM)
coupled with image processing for a detailed, nanoscale, qualitative and
quantitative study of industrially relevant Pt-zeolite Y catalyst.
Results and Discussion
Optimum imaging conditions enabled us for the first time to visualize and
locate in 3D thousands of Pt particles as small as 1 nm. Image analysis of 3D
reconstructions provided semi-automated measurement of valuable morphological
properties inaccessible to other techniques and facilitated comparison of the
impact of preparation procedures on
particle sizes, particle locations and particle-particle distances. In all of
the analyzed crystals prepared by incipient wetness impregnation (IWI) and
common heat treatments, the Pt size distribution was narrow with a mean diameter
of 1.0 - 1.3 nm, which is close to the size of zeolite Y micropore cavities.
Careful observation of the reconstructed volumes suggests that most of the Pt
particles were located inside the microporous crystalline regions, even when
their size exceeded the size of the micropore cavity. Thus, Pt particles are
assumed to grow to 1.2 – 3 nm diameter on the account of local destruction of
the zeolite Y lattice. To confirm this finding, impregnated zeolite was
submitted to direct reduction in H2 to promote Pt growth. The majority of Pt
particles were found to be still residing within microporous regions even
though they are larger than zeolite Y micropore cavities. This phenomenon has
been suggested in an earlier study , however, imaged here for the first time.
Surprisingly, a homogeneous distribution of Pt particles was observed in all of
the imaged zeolite crystals, however, the calculated Pt loading varied among
crystals from 0.2 to 7.1 wt% (Fig 1b). Interestingly, the variation in Pt
loading does not seem to influence size distribution of Pt particles, pointing
to their pronounced stability within micropore cavities.
Full Text Source (Subscription or Fee): https://nam.confex.com/nam/2013/webprogram/Paper7112.html
No comments:
Post a Comment