One-pot conversion of furfural to useful bio-products in the presence of a Sn,Al-containing zeolite beta catalyst prepared via post-synthesis routes Margarida M. Antunesa, Sérgio Limab, Patrícia Nevesa, Ana L. Magalhãesa, Enza Fazioc, Auguste Fernandesd, Fortunato Neric, Carlos M. Silvaa, Silvia M. Rochae, Maria F. Ribeirod, Martyn Pillingera, Atsushi Urakawab, Anabela A. Valentea,* a CICECO, Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal b Institute of Chemical Research of Catalonia, (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain c Dipartimento di Fisica e di Scienze della Terra, Università degli Studi di Messina, Viale F. Stagno d’Alcontres, 31 98166 Messina, Italy d Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Técnico, Av. Rovisco Pais, 1049001, Lisboa, Portugal e Department of Chemistry, QOPNA, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal ABSTRACT Aiming at the valorisation of furfural (Fur) via sustainable routes based on process intensification and heterogeneous catalysis, the one-pot conversion of this renewable platform chemical to useful bio-products, namely furfuryl alkyl ethers (FEs), levulinate esters (LEs), levulinic acid (LA), angelica lactones (AnLs) and -valerolactone (GVL), was investigated using a single heterogeneous catalyst, in 2-butanol, at 120 ºC. Various chemical 1 reactions are involved in this process, which requires catalysts with active sites for acid and reduction chemistry. For this purpose, it was explored for the first time the catalytic potentialities of modified versions of zeolite beta containing Al and Sn sites prepared from commercially available nanocrystaline zeolite beta via post-synthesis partial dealumination followed by solid-state ion-exchange. The post-synthesis conditions influenced considerably the catalytic performances of these types of materials. The best-performing catalyst was (Sn)SSIE-beta1 with Si/(Al+Sn)=19 (Sn/Al=27.6), which led to total yield of bio-products of 83% at 86% Fur conversion, and exhibited steady catalytic performance for six consecutive runs. A systematic catalytic study using the prepared catalysts with different bio-products as substrates, together with the molecular level and microstructural characterisation of the materials, helped understand the effects of different material properties on the specific reaction pathways in the overall system. These studies led to mechanistic insights into the reaction network of Fur to the bio-products in alcohol media, upon which a kinetic model was developed for the first time. The superior performance of (Sn)SSIE-beta1 in various steps was related to the dealumination degree, dispersion and amount of Sn-sites, and acid properties. Keywords: furfural; bio-products; zeolite beta; dealumination; solid state ion-exchange; acid catalysis; catalytic reduction 1. Introduction Furfural (Fur) is a renewable platform chemical and industrially produced from hemicelluloses [1]. It can be converted to the bio-products furfuryl alcohol (FA), furfuryl alkyl ethers (FEs), levulinate esters (LEs), levulinic acid (LA), angelica lactone isomers (AnLs) and -valerolactone (GVL) [2-4] (Scheme 1), useful in different sectors of the chemical industry. FA, industrially produced via hydrogenation of Fur, is used in the foundry 2 industry [5], and FEs are used as blending components of gasoline [6, 7] and as flavour compounds [8, 9]. LEs are used as oxygenate fuel additives [10-12], solvents, and to produce plasticizers and flavouring agents [13-14]. LA is used in the production of fuel additives [1521], agrochemicals (e.g. synthesis of -aminolevulinic acid, a biodegradable pesticide) [20, 22], and polymers (e.g. synthesis of diphenolic acid, an alternative to bisphenol A) [20, 23]. -Angelica lactone (AnL) is used for food flavouring and as aromas in the tobacco industry [24], pheromones [25] and fuel additives [14, 26], while GVL is used as solvent for biomassrelated reactions [27, 28], chemical intermediates [16-18, 29-33] and fuels [16, 17, 34, 35]. The conversion of Fur to the bio-products is complex because it involves acid and reduction chemistry. Hence, one-pot conversion of Fur to give desired bio-products in high yields using a heterogeneous catalyst is particularly challenging. Zeolites (crystalline microporous aluminosilicates) are versatile materials with various commercial applications, particularly as heterogeneous catalysts which led to important breakthroughs in refinery technologies. The potential application of zeolites can be extended to catalyst technology of future bio-refineries to convert biomass to fuels and chemicals, alleviating society’s dependence on (non-renewable) fossil fuels [3, 36, 37]. Among the most investigated zeolites, beta with BEA framework topology possesses a 3-D large-pore channel system and 12-membered ring channels. Zeolite beta and its modified versions are known to be effective catalysts for several reactions concerning the valorisation of biomass, e.g. corn fiber to Fur [38]; levuglucosan (an intermediate of (hemi)cellulose pyrolysis) to glucose [39] or Fur [40]; saccharides to Fur [41, 42], 5-(hydroxymethyl)furfural (HMF) [42-47], or LEs [48, 49]; cellulose and hemicelluloses to diesel [50]; hemicelluloses to polyols [51]; C-3 sugar to methyl lactate and lactic acid [52]; FA to 2-(ethoxymethyl)furfural (EMF) and ethyl levulinate (EL) [53]; biodegradable surfactants via acetalisation [54] or etherification of HMF [55]; Fur to GVL [4]; pyrolysis of biomass or derived compounds to aromatic/aliphatic 3 hydrocarbons [56-66]; sugarcane bagasse to bio-oil and upgrading to fuel [67]; co-conversion of biogenic waste and vegetable oil [68]; and pyrolysis of organosolv lignin to phenolic compounds [69, 70]. The introduction of different elements into zeolite beta widens its catalytic potential. In particular, tin-containing zeolite beta (Sn-beta) can promote chemoselective reduction of carbonyl groups to alcohol groups under relatively mild conditions via the Meerwein-Ponndorf-Verley (MPV) mechanism [71], avoiding the use of high pressure H2. Quantum chemical calculations indicated that Sn-beta stands on a similar footing to the classical compound Al(III)-isopropoxide used for MPV systems [72]. The method of preparing heterogeneous catalysts is an important factor from the practical point of view. The introduction of large Lewis acid centres such as Sn IV into zeolite beta typically involves tedious hydrothermal synthesis procedures, with several limitations: long synthesis times (due to slow nucleation), reduced number of isolated metal sites introduced and formation of relatively large crystals which can lead to internal diffusion limitations during the catalytic reaction [73]. An interesting strategy to overcome these limitations is using an up-scalable simple post-synthesis protocol involving dealumination and subsequent solid-state ion-exchange (SSIE). This protocol is advantageous in comparison to conventional liquid-phase routes in that it generates less toxic waste and avoids solvation of the metal species and hydrolysis of metal precursors which can impede the incorporation of the Lewis acid centres [74]. The modification of zeolite beta via SSIE was reported in 1993 by Barthomeuf et al. [75] to introduce lanthanum, and this procedure was more efficient than classical ion-exchange in solution, without destroying the zeolitic framework. Since then, different elements have been introduced into zeolite beta by SSIE leading to catalytic performances that are superior to those reached with the corresponding materials prepared using conventional liquid-phase routes [73, 76, 77]. Successful incorporation of tin into the BEA framework by SSIE was demonstrated by Hermans et al. [73, 75]. Zeolite beta was 4 partially dealuminated by acid treatment, generating vacant tetrahedral sites which were subsequently occupied by tin species introduced by SSIE. In the present work, modified versions of zeolite beta containing aluminium and tin sites were prepared from nanocrystalline NH4-beta via post-synthesis routes similar to those described by Hermans et al. [73]. Different materials were prepared by varying the acid concentration used for the partial dealumination, the amount of tin precursor used in the SSIE process, or by carrying out (Sn,Al)-competitive SSIE. The prepared (Sn,Al)-containing materials were explored as catalysts for the one-pot multistep conversion of Fur to the bioproducts, using 2-butanol (2BuOH) as reacting solvent, at 120 ºC. In order to help understand the effects of different material properties on the specific reaction pathways in the overall reaction system, the modified beta materials were also tested as catalysts for the reactions starting from FA, FEs, LEs, AnL and LA. These studies led to mechanistic insights into the complex reaction system, upon which a kinetic model was developed. 2. Experimental 2.1. Preparation of modified versions of zeolite beta Modified versions of beta catalysts were prepared from commercial nanocrystalline NH4-beta (Zeolyst, CP814E; based on the supplier´s technical information Si/Al=12.5, ca. 20-30 nm crystallite sizes [41]). First, NH4-beta was calcined at 550 ºC for 10 h under static air, giving H-beta. Subsequently, H-beta was modified with Sn in a similar fashion to that described by Hermans et al. [73], giving (Sn)SSIE-beta materials. Specifically, H-beta was partially dealuminated by acid treatment at 100 ºC for 20 h (HNO3 (70%, Sigma-Aldrich) was used to prepare acid solutions with the desired concentrations). The dealuminated materials denoted as deAl-beta1, deAl-beta2 and deAl-beta3 were obtained using decreasing acid concentration (Table 1). Subsequently, these materials were subjected to SSIE with tin. Solid mixtures of 5 tin(II) acetate (Sigma-Aldrich) and deAl-betan (n=1,2, or 3) were ground and mixed for 20 min at room temperature. After calcination at 550 ºC for 4 h, under air flow (20 mL min-1), (Sn)SSIE-betan (n=1,2, or 3) were obtained from the respective parent dealuminated materials, deAl-betan. A material denoted (SnAl)SSIE-beta1 was prepared from deAl-beta1 in a similar fashion to that for (Sn)SSIE-beta1, but using an equimolar mixture of tin(II) acetate and aluminium acetylacetonate (99%, Sigma-Aldrich) in the SSIE step prior to the calcination treatment. Bulk SnO2 was synthesised by treating tin(II) acetate under the same conditions to that used to prepare (Sn)SSIE-betan. Table 1. Modification conditions and textural properties of nanocrystalline H-beta and derived materials.a Post-synthesis conditions Sample Textural properties Dealuminationa SSIE b SBET Sext Vmicro [HNO3] (M) (mmol Sn(II)+Al(III)/gdeAl-beta) (m2g-1) (m2g-1) (cm3g-1) - - 650 204 0.18 deAl-beta1 13 - 583 190 0.16 deAl-beta2 7.2 - 554 176 0.15 deAl-beta3 4.3 - 543 179 0.14 (Sn)SSIE-beta1 13.0 0.846 559 170 0.16 (Sn)SSIE-beta2 7.2 0.421 569 181 0.16 (Sn)SSIE-beta3 4.3 0.210 573 180 0.16 (SnAl)SSIE-beta1 13.0 0.422(Sn)+0.422(Al) 566 181 0.15 H-beta a In the dealumination step (deAl) the volume of the acid solution per mass of H-beta was always 20 mL/gH-beta. b Amount of Al and/or Sn precursor used per gram of deAl-betan (n=1,2,3) used in the solid-state ion-exchange (SSIE) step. 6 2.2. Characterisation of the catalysts The wide-angle XRD patterns (10º < 2θ < 70º) were collected at room temperature on a D8 Advance Series 2 Theta/Theta powder diffraction system (Bruker) with Cu-Kα radiation and step size of 0.02º. Scanning electron microscopy (SEM) images, energy dispersive X-ray spectroscopy (EDS) analysis and elemental (Sn, Al, Si) mappings were obtained on a Hitachi SU-70 SEM microscope with a Bruker Quantax 400 detector operating at 20 kV. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analyses of all prepared samples were requested to the Central Analysis Laboratory (University of Aveiro); the measurements were carried out on a ICP-OES spectrometer Horiba Jobin Yvon modelo Activa M (detection limit of ca. 20 g.dm-3; experimental range of error of ca. 5%). Prior to the ICP-AES, the solids (10 mg) were digested by microwave with 1 mL of HF and 1 mL of HNO3, in a closed vessel at 180 ºC, followed by a second digestion with HCl. Nitrogen and argon adsorption-desorption isotherms were measured at -196 ºC and -186 ºC, respectively, on an Autosorb-iQ (Quantochrome Instruments). Prior to measurements, the solids were out-gassed at 300 °C for 12 h under vacuum. From the N2 adsorption isotherms the textural properties of the materials were calculated: the specific surface area (SBET) using the Brunauer-Emmett-Teller (BET) equation, (interparticle) mesopore size (Dmeso) distribution using the BJH method, external surface area (Sext) and micropore volume (Vmicro) using the t-plot method. The micropore size distribution was calculated from the Ar adsorption isotherm using non-local DFT method (cylindrical pore model) of the ASiQwin software (version 3.01). The 27 Al MAS NMR spectra of H-beta and (SnAl)SSIE-beta1 were recorded at 104.26 MHz using a Bruker Avance 400 (9.4 T) spectrometer with a contact time of 3 ms, a recycle delay of 1 s, and a spinning rate of 13 kHz. For the remaining materials (deAl-beta2, (Sn)SSIE-beta2, 7 deAl-beta1 and (Sn)SSIE-beta1, the 27 Al MAS NMR spectra were recorded at 182.432 MHz using a Bruker Avance III HD 700 (16.4 T) spectrometer with a unique pulse, a recycle delay of 1 s, and a spinning rate of 14 kHz. Chemical shifts are quoted in ppm from Al(NO3)3. Fourier transform infrared (FT-IR) spectra were recorded in transmission mode as KBr pellets using a Unican Mattson Mod 7000 spectrophotometer equipped with a DTGS CsI detector (400-4000 cm-1, 256 scans, 4 cm-1 resolution). Diffuse reflectance UV-vis spectra were recorded using a Jasco V-560 spectrophotometer and BaSO4 as reference. Raman measurements were carried out on a JobinYvon HR 800 UV-Raman spectrometer with the 325 nm He-Cd laser line. The thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) analyses were carried out under air with a heating rate of 10 ºC min-1, using Shimadzu TGA-50 and DSC-50 instruments, respectively. X-ray photoelectron spectroscopy (XPS) analysis was performed on a K-Alpha system from Thermo Scientific, equipped with a monochromatic Al K a source (1486.6 eV), and operating in constant analyser energy (CAE) mode, with a pass energy of 200 and 50 eV for survey and high resolution spectra, respectively. A spot size diameter of ca. 400 μm was adopted. Thus the measurements were carried out over large number of randomly oriented beta type crystallites, and the results represent fairly well the average chemical environment of the samples. The acid properties of the modified beta materials were measured using a NexusThermo Nicolet apparatus (64 scans and resolution of 4 cm-1) equipped with a specially designed cell, using self-supported discs (5–10 mg cm−2) and pyridine as the basic probe. Pyridine was chosen since its critical dimension of ca. 6.5 Å [78] is somewhat comparable with the molecular diameters of furfural (ca. 5.7 Å along the longest axis [79]). After in situ outgassing at 450 ºC for 3 h (10−6 mbar), pyridine (99.99%) was contacted with the sample at 150 ºC for 10 min and subsequently evacuated for 30 min under vacuum (10-6 mbar). The IR 8 bands at ca. 1540 and 1455 cm−1 are related to pyridine adsorbed on Brønsted (B) and Lewis (L) acid sites, respectively [80]. The acid properties of H-beta were considered the same as those reported by our group in ref. [41] for an identical sample, obtained from same NH4-beta recipient acquired. 2.3. Catalytic tests The batch catalytic experiments were performed in tubular glass reactors with pear-shaped bottoms and equipped with an appropriate PTFE-coated magnetic stirring bar and a valve. In a typical procedure, 0.45 M of furfural (Fur, Aldrich, 99%) and powdered catalyst (loading of 26.7 gcat L-1) in 0.75 mL of aliphatic alcohol (2-butanol (Sigma-Aldrich, 99%) or 2-propanol (Sigma-Aldrich, ≥99.5%)) were added to the reactor and heated at 120 oC. These reaction conditions are similar to those used by Román-Leshkov et al. [4]. Additionally, furfuryl alcohol (FA, Aldrich, 99%), 1-butyl levulinate (1BL, Aldrich, 98%), ethyl levulinate (EL, Aldrich, 99%), levulinic acid (LA, Aldrich, 98%), -angelica lactone (AnL, Alfa Aesar, 98%), furfuryl 1-butyl ether (1BMF, Manchester Organics, 95%) and furfuryl ethyl ether (EMF, Manchester Organics, 97%) were tested as substrates. The reaction mixtures were heated with a thermostatically controlled oil bath, under continuous magnetic stirring at 1000 rpm. Reaction time was calculated from the instant when the reactor was immersed in the oil bath. The catalytic performances of the different prepared materials were compared on the basis of similar mass of catalyst (important for practical applications). In order to examine the recyclability of the catalyst (here only (Sn)SSIE-beta1 was tested), after a batch run using Fur as substrate, the solid catalyst was separated from the reaction mixture by centrifugation, thoroughly washed with 2-butanol, dried at 85 ºC overnight, and calcined at 550 ºC for 3 h with a heating rate of 1 ºC min-1 to give the regenerated catalyst. 9 The catalyst was used in six consecutive batch runs under similar reaction conditions. In order to check for leaching and the presence of soluble active species, contact tests were performed as follows: the catalyst was treated for 24 h at 120 ºC under similar conditions to those used for typical batch runs, but without substrate. Subsequently, the mixture was cooled to room temperature, the solid catalyst was separated by centrifugation, and the liquid phase was passed through a filter containing a 0.2 m PTFE membrane. The substrate was added to the obtained liquid solution to give an initial substrate concentration of 0.45 M, and this solution was stirred at 120 ºC for 24 h. The evolution of the catalytic reactions was monitored by GC (for quantification of the bioproducts) and HPLC (for quantification of Fur). Prior to sampling, the reactors were cooled to ambient temperature before opening and work-up procedures. The analyses were always carried out for freshly prepared samples. The GC analyses were carried out using a Varian 3800 equipped with a capillary column (Chrompack, CP-SIL 5CB, 50 m × 0.32 mm × 0.5 μm) and a flame ionisation detector, using H2 as carrier gas. The HPLC analyses were carried out using a KnauerSmartline HPLC Pump 100 and a Shodex SH1011 H+ 300 mm × 8 mm (i.d.) ion exchange column (Showa Denko America, Inc., New York), coupled to a KnauerSmartline UV detector 2520 (254 nm) where the mobile phase was 0.005 M aq. H2SO4 at a flow rate of 0.8 mL min−1 and the column temperature was 50 oC. Calibration curves were measured for quantification. Individual experiments were performed for a given reaction time and the presented results are the mean values of at least two replicas. The substrate (Sub) conversion (%) at reaction time t was calculated using the formula: 100×[(initial concentration of Sub)-(concentration of Sub at time t)]/(initial concentration of Sub). The yield of product (Pro) (%) at reaction time t was calculated using the formula: 100×[(concentration of Pro at time t)/(initial concentration of Sub)]. The identification of the bio-products was checked by GC-MS using a Trace GC 2000 Series (Thermo Quest CE 10 Instruments)–DSQ II (Thermo Scientific), equipped with a capillary column (DB-5 MS, 30 m × 0.25 mm × 0.25 μm) using He as carrier gas. The bio-products (whenever formed) were furfuryl alcohol (FA), furfuryl alkyl ethers (2BMF=furfuryl 2-butyl ether, 2PMF=furfuryl 2propyl ether), levulinate esters (2BL=2-butyl levulinate, 1BL=1-butyl levulinate, EL=ethyl levulinate, 2PL=2-propyl levulinate), angelica lactones (AnL=-angelic lactone, AnL=angelic lactone), levulinic acid (LA), and -valerolactone (GVL). 2.4. Kinetic modelling The micro reactors were modelled as perfectly stirred batch reactors, and the mass balance equations are given by: V dCi  ri W dt Eq. (1) where V is the reaction mixture volume (L), W is the mass of catalyst (g), Ci is the molar concentration of the reactive species i (M), t is time (h), and ri is the overall reaction rate of species i expressed per unit of mass catalyst (mol·gcat-1·h-1). The ratio W/V was maintained constant in all experiments. Based on the mechanism proposed in section 3.2.3, a pseudo-homogeneous kinetic model was developed, considering first-order reactions for all steps involved: V dCFUR   k1  k9  CFUR W dt Eq. (2) V dCFA  k1 CFUR  k 2  k3  k10  CFA W dt Eq. (3) V dC2BMF  k 2 CFA  k 4  k5  k11  C2BMF W dt Eq. (4) V dCAnLs  k3 CFA  k 4 C2BMF  k 6  k12  CAnLs W dt Eq. (5) 11 V dCLA  k6 CAnLs  k7  k13  CLA W dt Eq. (6) V dC2BL  k5 C2BMF  k7 CLA  k8  k14  C2BL W dt Eq. (7) V dCGVL  k8 C2BL W dt Eq. (8) V dCD Fur  k9 CFur W dt Eq. (9) V dCD FA  k10 CFA W dt Eq. (10) V dCD 2BMF  k11 C2BMF W dt Eq. (11) V dCD AnLs  k12 CAnLs W dt Eq. (12) V dCD LA  k13 CLA W dt Eq. (13) V dCD 2 BL  k14 C2BL W dt Eq. (14) where k j are the apparent reaction kinetic constants (L·gcat-1·h-1) of step j at constant temperature. The problem was solved by numerical integration with simultaneous optimization, using appropriate initial conditions (at t=0). MEIGO (MEtaheuristics for systems biology and bIoinformatics Global Optimization) [81], an open-source toolbox for global optimization, and Matlab (version 7.8) were used to obtain the kinetic constants by fitting the model proposed to the experimental data (up to 7h) in order to minimize the following objective function:   2  np Fobj    Cm,n calc  Cm,n exp  m  n1  Eq. (14) 12 where Cm,n calc and Cm,n are the concentrations predicted by the model and the exp experimental ones, respectively, at each instant of time n, m is Fur, 2BMF, AnLs, LA, 2BL or GVL. 3. Results and Discussion 3.1. Characterisation of the modified zeolite beta materials Powder X-ray diffraction (XRD) patterns of the dealuminated materials (deAl-betan) are similar to that of H-beta (Figure 1), displaying reflections characteristic of the crystalline structure with BEA topology [41, 82-84]. The crystalline structure was preserved during the acid treatments, which is in agreement with the literature for HNO3-treated beta materials [83, 85-89]. The SSIE process did not lead to measurable changes in the crystalline structure of the materials deAl-betan. 13 Figure 1. Powder XRD patterns of H-beta and its modified versions, and SnO2 for comparison. Treatment of tin(II) acetate by calcination under identical conditions to those used to prepare the (Sn)SSIE-betan materials after SSIE, led to the cassiterite phase of SnO2 (member of the rutile group, JCPDS No. 41-1445): 2 = 26.6, 33.9, 38, 52.7 and 54.7º, corresponding to the reflections (100), (101), (200), (211) and (220), respectively), which consists of [SnO6]8octahedra [90, 91]. The bulk tin oxide sample (hereafter denoted SnO2 for the sake of simplicity) seems to be mixed with relatively small amounts of other tin oxide phases; a peak at 27º may be due to Sn2O3 (JCPDS No. 25-1259), and a peak at 31.7º may be due to triclinic Sn3O4 (JCPDS No. 16-757). No crystalline phases of tin oxide could be distinguished in the XRD pattern of (Sn)SSIE-beta1. For the remaining Sn-containing beta materials (especially 14 (SnAl)SSIE-beta1) a weak peak at ca. 52º not related to the BEA framework structure, was observed, which may be due to crystalline SnO2 and heterogeneous dispersion of Sn in these materials. Zeolite H-beta and the corresponding modified materials exhibited reversible N2 adsorptiondesorption isotherms with features of Type I. The significant increase in N2 uptake at low relative pressures (p/p0< 0.1) can be attributed to the filling of micropores (Figure S1). The N2 uptake increases again significantly as p/p0 approaches unity, which is likely due to multilayer adsorption on the external surface of the crystallites. The specific surface area and pore volume of H-beta decreased slightly after the acid treatments (Table 1). Comparison of the micropore size distribution of deAl-beta1 and the corresponding (Sn)SSIE-beta1 material showed no considerable changes in pore sizes after the SSIE (the maxima at ca. 5.8 and 6.1 Å for deAl-beta1 and (Sn)SSIE-beta1, respectively, Figure S2). In general, the texture parameters of the modified materials are comparable (SBET of 543-583 m2g-1, Sext of 170-190 m2g-1,Vmicro of 0.14-0.16 cm3g-1, Table 1). The SBET values are in the range of values reported in the literature for Sn-beta materials prepared using different synthetic approaches [73, 82, 92, 93]. The materials possess considerable Sext and ratios Sext/Vmicro, which is consistent with the fact they were prepared from nano-sized crystallites of zeolite beta (ca. 20-30 nm [41]). On the other hand, the post-synthesis treatments did not cause significant structural collapse or pore blockage. All modified beta materials consist of irregular shaped aggregates of crystallites, with homogeneous dispersions of Al and Si as observed by SEM and elemental mapping (Figures 2 and 3). The Sn mapping showed fairly homogeneous dispersion of surface species in the case of (Sn)SSIE-beta1, whereas for the remaining Sn-containing beta materials, regions with higher concentrations of Sn were found, showing heterogeneous dispersion of Sn. These results are consistent with the powder XRD data of the Sn-containing solids. 15 Figure 2. SEM and elemental mapping of Si and Al for deAl-beta1 (a), deAl-beta2 (b) and deAl-beta3 (c). The compositions of the modified beta materials were determined by ICP-AES analyses (Table 2). The dealumination of H-beta using increasingly concentrated HNO3 led increasing molar ratios Si/Al of the materials deAl-betan, and thus the dealumination degree increased in the order, deAl-beta3