The nature and spectroscopic expression of external surface sites of zeolites, in particular ZSM-5, is a long-debated question. Herein, we use three cutting-edge techniques: Fouriertransform infrared spectroscopy (FTIR) with Fourier selfdeconvolution (FSD), high magnetic field proton NMR spectroscopy under fast magic-angle spinning (MAS) and periodic boundary Density Functional Theory (DFT) calculations to study external surface models and analyze the effect of crystallite size. This provides an unequaled description of the various kinds of hydroxyl groups and of their proximities. The hydrogen-bond donor, acceptor or isolated nature of the hydroxyls results in distinct signals both in FTIR and NMR spectra, but the peak assignment is not the same from one technique to the other when the chemical nature of the hydroxyl changes. Bridging Si−(OH)− Al groups and Al−(H 2 O) lead to overlapping signals in one-dimensional 1 H MAS NMR, whereas their contributions are strongly different in FTIR spectra. However, quantification and proximity assessment could only be obtained by 1 H MAS NMR. With DFT, we confirm previous assignments for silanols and Si−(OH)−Al bridging OH groups. Other signals (between 3750 and 3600 cm −1 , and between 1 and 4 ppm) are not only assigned to extra-framework species (which we confirm with dedicated models), but also enclose the signature of sites exposed at the external surface of ZSM-5. In particular, Al−(H 2 O) species (∼3665 cm −1 ; 3.8, 2.6 ppm) and silanol−Al (∼3740, 3720, 3665 cm −1 ; 2.6, 2.2 ppm) contribute to several features depending on their environment. μ 1 -Al−OH are also present at the external surface in low amount, with a 3780 cm −1 signal in IR, and weak signals in the 0−2 ppm interval in 1 H MAS NMR.

We reveal the presence of significant variations in Brønsted catalytic activity within and between individual H-ZSM-5 zeolite crystals. Fluorescence microscopy in combinationw ith a fluorogenic probe was used to resolve the catalytic activity at the nanoscale. The observed variations in catalytic activity could be directly linked to structural parameters and crystal morphology observed in scanninge lectron microscopy and by specifically stainingc rystal defects. The obtained resultsa re directly comparedw ith ensemblea veraged information from techniques such as pyridine IR spectroscopy and nitrogen physisorption, typically used to characterize acid zeolites. The inter-and intra-particle heterogeneities resolved by the employed fluorescence approach remainu naddressed by bulk characterization. Our experimental resultsr elate the heterogeneous catalytic activity to variation in both the Si/Al ratio and mesoporosity inducedd uring the zeolite synthesis.The preparation of zeolite-based industrial catalysts usually involves mixingt he zeolitesw ith silicaa nd or aluminab inders in order to dilute the zeolite properties and to obtain the desired throughput. [1][2][3] During this process it is assumed that the zeolite crystalsthemselves are homogeneous in nature, [2,4,5] that is, only small variations in properties between the zeolite crystals in ab atch exist. However,i fthis assumption is wrong and large variations in, for example, acid site density are present, parts of the shaped catalystc ould become more active than others,r esulting in undesired coke formation and thus al oss in catalystactivity and lifetime. [4,6,7] Twop arameters impacting catalyst activity are the number and strength of acid sites present in az eolite. These are directly relatedt ot he framework Al content, [8,9] hence Al determination is often used to assess zeolite acidity.S everalt echniques can be used to determine the Si/Al ratio, yielding powder averaged information, for example, elemental analysisu sing inductive coupled plasma (ICP), [10,11] magic angle spinning (MAS) 29 Si and 27 Al NMR, [8,12] laser induced break down spectroscopy (LIBS), [13] X-ray photon electron spectroscopy (XPS) [12,14] and time of flight-secondary ion mass spectrometry (TOF-SIMS). [15,16] All of theset echniques lead to the determination of the 'bulk" scale acidity and some are even able to obtain single crystal information given that crystal sizes and aluminum content are sufficiently large; [17] for example, single crystal X-ray diffraction [17,18] and energy dispersive X-ray spectroscopy (EDX) coupled to electron microscopy potentially with focused-ion-beam milling. [14,19] In summary,t he acidic properties of zeolitesa re often deduced indirectly from the aluminum content.F urther,n oi nformation regarding site accessibility is obtained in these results. Direct measurements of acid site density and strengtha re possible via temperature programmed desorption (TPD) [8,14,20] and infrared- [2,21,22] or Raman spectroscopy [23] using basic probe molecules such...

Shaping is a crucial step in the preparation of catalysts at the industrial scale, but a rationalized understanding of how binders impact the catalyst's performance is still far from apparent. In this work, the effect of shaping with common binders (boehmite, γ-Al 2 O 3 , and silica) on the acidity and catalytic properties of an acid zeolite catalyst, H-ZSM-5, is probed. The zeolite−binder samples (1:1 ratio) are shaped following commonly employed procedures and analyzed using both conventional characterizations of the acidity and porosity as well as using advanced fluorescence microspectroscopic characterization. In the latter approach, the fluorescence intensity stemming from the Brønsted acidcatalyzed furfuryl alcohol oligomerization is used to determine in detail the effect of shaping on acid zeolite's catalytic activity. Through density functional theory calculations, the observed changes in catalytic performance are assigned to atomic-scale processes such as the interaction of acid sites with binder-related molecular species and the migration of ions. The most detrimental effects related to shaping are migration of cations, here Na + , from the binder to the zeolite, which is an important mechanism for silica binders, as well as pore blockage by alumina and silica species. Strong acid sites are also likely to be converted into weak ones upon interaction with binders. A counterbalancing effect is the genesis of some additional bridging OH groups upon filling of local defects with alumina species from alumina binders. With such knowledge in hand, it becomes possible to balance these effects to get the desired properties.