The disordered structure of silica zeolite EU-20b, obtained by topotactic condensation of the piperazinium containing layer silicate EU-19

Zeolite EU-20b was prepared by heating the piperazinium containing layer silicate EU-19 in air at 1000 °C. The microporous silica framework of EU-20b forms by topotactic condensation of the silicate layers of the crystalline precursor EU-19. According to the observed diffraction data, the EU-20b structure is closely related to the (orthorhombic) CAS zeolite framework type. However, the diffraction pattern revealed structural disorder of the material as indicated by the presence of sharp and broad reflections. In spite of the disorder, the XRD pattern of EU-20b can unambiguously be indexed based on a C-centered orthorhombic unit cell with lattice parameters a₀ = 13.817(4) Å, b₀ = 4.995(1) Å, c₀ = 16.637 (5) Å. The program DIFFaX was used to simulate diffraction diagrams of various stacking disordered silica-materials made up by layer-like building units. The best fit between simulated and observed patterns was obtained for a probability of about 88% CAS-type stacking and 12% NSI-type stacking. EU-20b is a small pore zeolite characterized by a one-dimensional pore system consisting of straight and non-intersecting 8-ring channels and has a very high framework density of ≈20.8 T/1000 Å³. Although the pore volume of EU-20b is free of organic pore fillers due to the heating process at 1000 °C, nitrogen sorption experiments showed that there is no “free” access to the pore volume. Two effects might block access to the pores: According to ²⁹Si MAS NMR spectroscopy a few defects are probably present caused by incomplete or random condensation of the silanol groups and the elliptical pores are very small in one direction (2.3–2.5 Å) compared to N₂ (kinetic diameter 3.64 Å). Thus, EU-20b is formally porous by topology, but apparently non-porous to N₂.     

Algorithms and tools for high-throughput geometry-based analysis of crystalline porous materials

Crystalline porous materials have a variety of uses, such as for catalysis and separation. Identifying suitable materials for a given application can, in principle, be done by screening material databases. Such a screening requires automated high-throughput analysis tools that calculate structural properties for all materials contained in a database so they can be compared with search queries, grouped or classified. One important aspect of the structural analysis of materials such as zeolites and metal organic frameworks is the investigation of the geometrical parameters describing pores. Here, we present algorithms and tools to efficiently calculate some of these important parameters. Our tools are based on the Voronoi decomposition, which for a given arrangement of atoms in a periodic domain provides a graph representation of the void space. The resulting Voronoi network is analyzed to obtain the diameter of the largest included sphere and the largest free sphere, which are two geometrical parameters that are frequently used to describe pore geometry. Accessibility of nodes in the network is also determined for a given guest molecule and the resulting information is later used to retrieve dimensionality of channel systems as well as in Monte Carlo sampling of accessible surfaces and volumes. The presented algorithms are implemented in a software tool, Zeo++, which includes a modified version of the Voro++ library. We present example applications of our algorithms and tools using zeolite frameworks currently listed in the Atlas of Zeolite Frameworks.     

Synthesis of a new molecular sieve using DABCO-based structure-directing agent

A new 1,4-diazabicyclo[2.2.2]octane (DABCO)-based quaternary ammonium compound is designed, synthesized, and used as structure-directing agent (SDA) for molecular sieve synthesis. Several 1,1′-alkylenedi(4-aza-1-azonia-2,5-dimethylbicyclo[2.2.2]octane) type SDAs are used in all-silica synthesis mixtures. Among the SDAs tested, the use of 1,1′-butylenedi(4-aza-1-azonia-2,5-dimethylbicyclo[2.2.2]octane) gives a new phase (GUS-1), whereas the use of other SDAs gives zeolite beta (^*BEA), ZSM-12 (MTW), and ZSM-5 (MFI). The GUS-1 is indexed in the orthorhombic crystal class with refined lattice constants a=16.4206(4) Å, b=20.0540(4) Å and c=5.0464(1) Å. The crystalline architecture of GUS-1 shows the same [0 0 1] projection of the framework as that of mordenite (MOR), and is characterized by a one-dimensional 12-membered ring channel system that is closely related to the channels of ZSM-12. The GUS-1 is stable to heat upon calcination at 700 °C in air. The calcined material exhibits adsorption capacity that is comparable to typical large-pore one-dimensional microporous silicates. The behavior of the SDA during synthesis is also discussed.     

(CH3CH[NH3]CH2NH3)1/2·ZnPO4, a zincophosphate analogue of aluminosilicate zeolite thomsonite

The synthesis and structure of (CH₃CH[NH₃]CH₂NH₃)_1/2·ZnPO₄, an organically templated zincophosphate (ZnPO) analogue of aluminosilicate zeolite thomsonite (THO), are described. The ZnPO framework is built up from an alternating, vertex-sharing, network of ZnO₄ and PO₄ groups (d_av(Zn–O)=1.944 (8) Å, d_av(P–O)=1.535 (9) Å, θ_av(Zn–O–P)=130.5°) involving distinctive 4=1 secondary building units. The 1,2-diammonium propane cations are highly disordered in the [0 0 1] 8-ring channels. Crystal data: (CH₃CH[NH₃]CH₂NH₃)_1/2·ZnPO₄, M_r=198.42, orthorhombic, space group Pncn (no. 52), a=14.119 (6) Å, b=14.136 (5) Å, c=12.985 (5) Å, V=2591 (3) ų, Z=10, R(F)=0.057, R_w(F)=0.061 (for a twinned crystal).     

Preparation and crystal structure of RUB-18 modified for synthesis of zeolite RWR by topotactic conversion

The systematic study on the synthetic route of the siliceous zeolite RWR with a small 8-MR straight channel by topotactic conversion of crystalline layered silicate RUB-18 was carried out by using several topotactic precursors obtained from Na-RUB-18. Intermediate layered structures of topotactic precursors were designed by intercalation of amine molecules and acid treatment. Crystal structures of two kinds of TMAOH intercalated RUB-18s (TMA-RUB-18-poly1 and TMA-RUB-18-poly2) and their acidified TMA-RUB-18 were determined by ab initio structure analysis using X-ray powder diffraction data. The layered structure of TMA-RUB-18-poly1 and TMA-RUB-18-poly2 had tetragonal symmetry of space group P4₂/nmc, and the lattice parameters were estimated to be a = 7.4121 Å, c = 22.615 Å for TMA-RUB-18-poly1 and a = 7.3718 Å, c = 29.342 Å for TMA-RUB-18-poly2. Two silicate layers were involved in a unit-cell and TMA⁺ cations were intercalated in the interlayer. The layer stacking sequence was completely different from that of Na-RUB-18. Structure of acidified TMA-RUB-18 had also tetragonal symmetry of space group I4₁/amd and lattice parameters a = 7.4722 Å, c = 37.242 Å with four silica layers. Stacking sequence in acidified TMA-RUB-18 was similar to that of Na-RUB-18 although a large shrinking of interlayer distance (ca. 2.0 Å) was observed. In the acidified TMA-RUB-18, one-dimensional pseudo pore was constructed by semi-circular geometry derived from the framework structure and stabilized by formation of hydrogen bonding between the terminal silanol groups, which faced each other with atomic distance d(O–O) of ca. 2.5 Å. By the dehydration–condensation of silanol groups during careful calcination, zeolite RWR could be successfully prepared from the acidified TMA-RUB-18.     

Studies of Cu-ZSM-5 by X-ray absorption spectroscopy and its application for the oxidation of benzene to phenol by air

The oxidation of benzene to phenol has been successfully carried out in air over Cu-ZSM-5 at moderate temperatures. Several parameters such as Cu loading, calcination temperature and co-exchanged metal ions influence the nature of the catalyst. At low Cu loadings, the catalyst is more selective to phenol while at high Cu loadings CO₂ is the major product. In situ H₂-TPR XAFS studies reveal that at low Cu loadings, Cu exists as isolated pentacoordinated ions, with 4 equatorial oxygens at 1.94 Å and a more distant axial oxygen at 2.34 Å. At higher loadings, monomeric as well as dimeric Cu species exist, with a Cu–Cu distance of 2.92 Å. This suggests that the isolated Cu sites are the active sites responsible for phenol formation. When the catalyst was calcined at 450 °C, the activity peaked in the first hour and then slowly deactivated, but when the calcination temperature was increased to 850 °C, the activity slowly increased until it reached a plateau. Analysis of the XANES region during in situ H₂-TPR shows that at lower calcination temperatures two reduction peaks are present, corresponding to Cu²⁺ → Cu⁺ and Cu⁺ → Cu⁰. At high calcination temperatures, only a small fraction of the Cu undergoes the two-step reduction and most of the Cu remains in the +2 state. Slow deactivation of the catalyst calcined at 450 °C is due to migration of the Cu ions to inaccessible sites in the zeolite; at high calcination temperatures the Cu is tightly bound to the framework and is unable to migrate. EXAFS analysis of the sample calcined at 850 °C reveals two Cu–Si(Al) scattering paths at 2.83 Å. Doping the catalyst with other metals, in particular Ag and Pd, further improves the activity and selectivity of the reaction. The addition of water to the reaction increases the selectivity of the reaction by displacing the product from the active site.     

Three metal-organic frameworks prepared from mixed solvents of DMF and HAc

Three metal-organic framework compounds [HZn₃(OH)(BTC)₂(2H₂O) (DMF)] · H₂O (MOF-CJ3), [Co₆(BTC)₂(HCOO)₆(DMF)₆] (MOF-CJ4), and [Co₁₈(HCOO)₃₆] · 3H₂O (MOF-CJ5) have been solvothermally synthesized in mixed solvents of DMF and HAc, respectively. These MOFs are characterized by single-crystal X-ray diffraction, X-ray powder diffraction, ICP, TG analyses, IR, and photoluminescence spectroscopy analyses. MOF-CJ3 crystallizes in tetragonal, space group I4cm (No. 108) with a = 20.588(3) Å, b = 20.588(3) Å, c = 17.832(4) Å. Its framework can be described as a 3D decorated (3, 6)-connected net based on the assembly of trigonal prismatic SBUs and triangular links. MOF-CJ4 crystallizes in hexagonal, space group P-3 (No. 147) with a = 13.975(2) Å, b = 13.975(2) Å, c = 8.1650(16) Å. The 2D network of MOF-CJ4 is constructed from [Co₆(R(CO₂)₃)₂(HCO₂)₆(DMF)₆] (R = C₉H₃–) clusters and 1,3,5-benzene-tricarboxylates linkers. MOF-CJ5 crystallizes in triclinic, space group (No. 2) with a = 15.205(3) Å, b = 18.005(4) Å, c = 21.500(4) Å,  = 71.21(3)°, β = 84.47(3)°, γ = 67.15(3)°. MOF-CJ5 has a diamond framework with Co-centered CoCo₄ tetrahedra as nodes. It is noteworthy that the formic ligands in MOF-CJ4 and MOF-CJ5 are generated by the decomposition of DMF under acid conditions and incorporated into these two compounds.     

The influence of zeolite acidity for the coupled hydrogenation and ring opening of 1-methylnaphthalene on Pt/USY catalysts

The influence of framework and extraframework composition of USY zeolite on the catalytic performance of bifunctional Pt/USY (1 wt.% Pt) catalysts for the coupled hydrogenation and ring opening of 1-methylnaphthalene (1-MN) has been studied on a continuous fixed bed high pressure reactor. All Pt/USY catalysts showed very high methylnaphthalene (MN) conversions under the reaction conditions studied (T=300–375 °C, P=4.0 MPa, WHSV=2 h⁻¹, H₂/1-MN=30 mol/mol). Product yields and selectivities were mainly determined by the zeolite composition (i.e. acidity). Selectivity to products with the same number of carbon atoms than the feed (C11) increased, at constant temperature, with decreasing the Brönsted acidity of the USY zeolite, that is, with decreasing the concentration of framework Al (FAL) and increasing extraframework Al (EFAL). Selectivity to high cetane ring opening products (ROP=C11-alkylbenzenes (C11AB) and C11-alkylcycloalkanes) within the C11 fraction was higher for the less acidic catalysts. A maximum yield of ROP of ca. 15 wt.% at a C11 yield of ca. 73 wt.% was obtained at 350 °C (P=4.0 MPa, WHSV=2 h⁻¹, H₂/1-MN=30 mol/mol) for a USY zeolite with an intermediate degree of dealumination (a₀=24.33 Å) and containing all the EFAL (bulk Si/Al ratio of 2.6). For this catalyst, a slight increase in ROP yield (ca. 17 wt.%) at similar C11 yield (ca. 74 wt.%) was obtained by working at lower temperature (300 °C) and lower space velocity. Increasing the reaction pressure above 4.0 MPa had only a marginal influence on product yields and selectivities.     

Crystal structures of fully dehydrated fully Sr-exchanged zeolite X and of its ammonia sorption complex

The crystal structures of fully dehydrated Sr₄₆–X [Sr₄₆Si₁₀₀Al₉₂O₃₈₄; a=25.214(7) Å] and of its ammonia sorption complex, Sr₄₆–X·102NH₃ [Sr₄₆Si₁₀₀Al₉₂O₃₈₄·102NH₃; a=25.127(7) Å], have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd at 21(1)°C. The Sr₄₆–X crystal was prepared by ion exchange in a flowing stream of aqueous 0.05 M Sr(ClO₄)₂ for 5 days followed by dehydration at 360°C and 2×10⁻⁶ Torr for 2 days. To prepare the ammonia sorption complex, another dehydrated Sr₄₆–X crystal was exposed to 230 Torr of zeolitically dried ammonia gas for 1 h followed by evacuation for 12 h at 21(1)°C and 5×10⁻⁴ Torr. The structures were refined to the final error indices, R₁=0.043 and R_w=0.039 with 466 reflections, and R₁=0.049 and R_w=0.044 with 382 reflections, for which I>3σ(I). In dehydrated Sr₄₆–X, all Sr²⁺ ions are located at two crystallographic sites. 16 Sr²⁺ ions are at the centers of the double six-rings, filling that site (site I, Sr–O=2.592(6) Å). The remaining 30 Sr²⁺ ions are in the supercage (site II); each extends 0.56 Å into the supercage from the plane of its three nearest oxygen atoms (Sr–O=2.469(6) Å). In the structure of Sr₄₆–X·102NH₃, the Sr²⁺ ions are located at three crystallographic sites: 12 are found at site I [Sr–O=2.652(10) Å]; four in the sodalite units (site I′) each coordinated to three framework oxygen atoms at 2.654(9) Å and also to three ammonia molecules at 2.76(8) Å. The remaining 30 Sr²⁺ ions lie at site II. Each extends 1.12 Å into the supercage where it coordinates to three framework oxygen atoms at 2.584(7) Å and also to three ammonia molecules at 2.774(24) Å.     

Silica supported cobalt Fischer–Tropsch catalysts: effect of pore diameter of support

The influence of the effect of average pore diameter of silica support on the physical and chemical properties of supported cobalt catalysts and their performance in the Fischer–Tropsch synthesis was investigated. Silicas with different mean pore diameter (20, 40, 60, 100 and 150 Å) were impregnated with cobalt nitrate to produce catalysts containing 20 wt.% cobalt. The metal crystallite size and degree of reduction was found to increase with increasing pore diameter of the support for supports with an average pore diameter larger or equal to 40 Å, and hence the dispersion decreased. In impregnated catalysts, the metal crystallites seems to appear in clusters on the support. With increasing average pore diameter, the size of these clusters increases. In the Fischer–Tropsch synthesis, the 100 Å supported catalyst proved to be the most active and selective catalyst for hydrocarbon formation. The C₅₊ and methane selectivity passed through a maximum and minimum at the 100 Å supported catalyst, respectively, which can be explained quantitatively using the reactant transport model proposed by Iglesia et al.     

Ionic conductivity of single-crystal ferrierite

Ionic conduction in a single-crystal zeolite is reported for the first time. Sub-millimeter sized ferrierite is grown by an organothermal method, and the conduction of sodium cation is measured along [0 0 1] and [0 1 0] separately by a.c. impedance analysis. The main conduction along [0 0 1] is through ten-member ring channels, while that along [0 1 0] is through eight-member ring channels. The measurement at 673–873 K reveals that the conductivity along [0 1 0] is greater than along [0 0 1]. The activation energy along [0 1 0] (1.2 eV) was greater than that (0.84 eV) along [0 0 1]. These differences are discussed in view of the ferrierite framework structure.     

High-quality, oriented and mesostructured organosilica monolith as a potential UV sensor

We synthesized high-quality and oriented periodic mesoporous organosilica (PMO) monoliths through a solvent evaporation process using a wide range of mole ratios of the components: 0.17–0.56 1,2-bis(triethoxysilyl)ethane (BTSE): 0.2 cetyltrimethylammonium chloride (CTACl): 0–1.8 × 10⁻³ HCl: 0–80 EtOH: 5–400 H₂O. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images indicated that the mesoporous channels within the monolith samples were oriented parallel to the flat external surface of the PMO monolith and possessed a hexagonal symmetry lattice (p6mm). The PMO monolith synthesized from a reactant composition of 0.35 BTSE: 0.2 CTACl: 1.8 × 10⁻⁶ HCl: 10 EtOH: 10 H₂O had a pore diameter, pore volume, and surface area – obtained from an N₂ sorption isotherm – of 25.0 Å, 0.96 cm³ g⁻¹ and 1231 m² g⁻¹, respectively. After calcination at 280 °C for 2 h in N₂ flow, the PMO monolith retained monolith-shape and mesostructure. Pore diameter and surface area of the calcined PMO monolith sample were 19.8 Å, 0.53 cm³ g⁻¹ and 1368 m² g⁻¹, respectively. We performed ²⁹Si and ¹³C CP MAS NMR spectroscopy experiments to confirm the presence of Si–C bonding within the framework of the PMO monoliths. We investigated the thermal stability of the PMO monoliths through thermogravimetric analysis (TGA). In addition, rare-earth ions (Eu³⁺, Tb³⁺ and Tm³⁺) were doped into the monoliths. Optical properties of those Eu³⁺, Tb³⁺ and Tm³⁺-doped PMO monoliths were investigated by photoluminescence (PL) spectra to evaluate their potential applicability as UV sensors.     

Structure of a cyclopropane sorption complex of dehydrated fully Mn-exchanged zeolite X

The structure of a cyclopropane sorption complex of dehydrated fully Mn²⁺-exchanged zeolite X, Mn₄₆Si₁₀₀Al₉₂O₃₈₄ · 30C₃H₆ (a=24.690(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group at 21(1)°C. The crystal was prepared by ion exchange in a flowing stream of 0.05 M aqueous Mn(NO₃)₂ for three days, followed by dehydration at 460°C and 2×10⁻⁶ Torr for two days, and exposure to 100 Torr of cyclopropane gas at 21(1)°C. The structure was determined in this atmosphere and was refined to the final error indices R₁=0.065 and R₂=0.071 with 509 reflections for which I>3σ (I). In this structure, Mn²⁺ ions are located at two crystallographic sites. Sixteen Mn²⁺ ions fill the octahedral site I at the centers of the hexagonal prisms (Mn–O=2.290(9) Å). The remaining 30 Mn²⁺ ions are at site II; each extends 0.41 Å into the supercage (an increase of 0.27 Å upon C₃H₆ sorption as compared to fully dehydrated Mn₄₆Si₁₀₀Al₉₂O₃₈₄) where it coordinates to three trigonally arranged framework oxygens at 2.148(8) Å and complexes weakly and facially to a cyclopropane molecule by a primarily quadrupolar interaction. The carbon atoms of each cyclopropane molecule are equivalent and equidistant from its Mn²⁺ ion (Mn–C=2.95(9) Å). Because of high thermal motion, the C–C bond length is inaccurately determined; the value found, 1.21(8) Å, is too small.     

Multinuclear MAS NMR studies of zeolites MCM-22 and MCM-49

MCM-22 and MCM-49 comprise a new class of molecular sieves that crystallizes as thin sheets or platelets and has many unusual structural features. MCM-22 is first synthesized hydrothermally as a precursor, MCM-22(P), that condenses upon calcination to a three-dimensional framework (MCM-22). Its framework topology is comprised of two independent pore systems, both accessible through 10-membered rings. One of these pore systems is defined by two-dimensional sinusoidal channels, which maintain an effective 10-ring diameter throughout the structure. The other consists of large supercages whose inner free diameter, 7.1 Å, is defined by 12 rings with inner height of 18.2 Å. MCM-49 has the same framework topology as MCM-22, but is synthesized directly in the reaction gel and therefore still contains the organic template. Multinuclear MAS NMR studies of MCM-22 (P), MCM-22, and MCM-49 are presented and discussed in light of the proposed structure and provide new insights into this novel class of materials. The structural information obtained from this NMR investigation is complementary to and consistent with the structure proposed from X-ray diffraction measurements. ¹³C NMR data support the existence of different dual pore systems within both MCM-22(P) and MCM-49. ²⁷Al MAS NMR spectra exhibit three distinct T_d resonances that can be interpreted in terms of the proposed framework topology. ²⁹Si MAS studies of a highly siliceous MCM-22 prepared by hydrothermal dealumination confirm the presence of at least one buried T-site in its framework structure that is not accessible to a channel wall, favor the orthorhombic form of the proposed structure, and support the presence of the modified dodecasil-1H cage.     

Surface properties of porous carbons obtained from polystyrene-based polymers within inorganic templates: role of polymer chemistry and inorganic template pore structure

Three inorganic adsorbents were applied as templates to produce porous carbons from polystyrene-based organic polymers. As matrices, amorphous silica gel, mesoporous alumina and microporous zeolite 13X were used. Organic precursors were polystyrene sulfonic acid (co-maleic acid) sodium salt and polystyrene co-maleic acid isobutyl/methyl mixed ester. The impregnated templates were carbonized at 800 °C. After removal of inorganic matrices porous carbons were obtained. Materials were characterized by adsorption of nitrogen, thermal analysis, potentiometric titration and SEM. Owing to the template carbonization, highly mesoporous carbons were obtained (S_BET up to 1500 m²/g, V_t up to 3 cm³/g) with majority of pores with sizes between 20–200 Å. Although the carbons were not replicas of their matrices, the carbonization within the confined space with utilization of self-released pore formers resulted in unique carbonaceous materials with very acidic surface. That acidity is linked to either exothermic effect of sodium reactivity with moist air or susceptibility for air oxidation of small graphene layers formed in the confined pore space.     

The location of pyridine in sodium–silver–Y zeolite by powder synchrotron X-ray diffraction

The powder synchrotron X-ray diffraction pattern of a mixed sodium–silver–Y zeolite, Ag_56−xNa_xSi₁₃₆Al₅₆O₃₈₄ x≈19, saturated with pyridine, has been analysed by the Rietveld method to reveal positions for the adsorbed molecules. Cations are distributed over three sites, SII, constrained to 100% occupancy, with 17.2(1) and 14.8(1) Ag(1) and Na(1) ions per unit cell, respectively, SI′ with 18.3(1) Ag(2) ions per cell, and SI with 1.8(1) Ag(3) ions per cell. The refinement suggests that approximately 7.5 pyridine molecules are adsorbed per supercage, located in two sites within the cavities of the zeolite. Pyridine(1) is in the 12-ring window connecting supercages. Three molecules project through each window and approach the SII cations in a supercage, with an average Ag(1)–N distance of 3.17(2) Å. An SII cation can be linked to three pyridine(1) molecules from three separate windows. These sites are full with 5.98(2) molecules per supercage. Pyridine(2) is found in the supercage, oriented with its π electron density towards the SII cations, with its centre at 2.87(2) Å from Ag(1). The average occupancy was fixed at 1.5 molecules per supercage, corresponding to 20% of the pyridine content. A local ordering scheme can be postulated, whereby alternate supercages are filled by pyridine(1) and pyridine(2) molecules, efficiently filling the channels of the zeolite.     

Structure, energetics and diffusion properties of isomers of trimethyl benzene in β zeolite: Uptake and Monte Carlo simulation study

A Monte Carlo study along with experimental uptake measurements of 1,2,3-trimethyl benzene, 1,2,4-trimethyl benzene and 1,3,5-trimethyl benzene (TMB) in β zeolite is reported. The TraPPE potential has been employed for hydrocarbon interaction and harmonic potential of Demontis for modeling framework of the zeolite. Structure, energetics and dynamics of TMB in zeolite β from Monte Carlo runs reveal interesting information about the diameter, properties of these isomers on confinement. Of the three isomers, 135TMB is supposed to have the largest diameter. It is seen TraPPE with Demontis potential predicts a restricted motion of 135TMB in the channels of zeolite β. Experimentally, 135TMB has the highest transport diffusivity whereas MD results suggest this has the lowest self diffusivity.     

Fluid catalytic cracking: some recent developments in catalyst particle design and unit hardware

Catalytic cracking is an old process, but is still subject to new pressures for change and improvement. In the 1990s, these pressures arise from the need to crack components drawn from deeper down the barrel as well as to reformulate fuel products which can meet more stringent environmental requirements. Recent efforts at correlating catalyst formulation and cracking performance still rely on largely empirical understanding of the role of catalyst composition and zeolite/matrix pore architecture. However, new tests measuring cracking performance at constant surface area as the zeolite/ matrix ratio varies have indicated that the pore architecture should be designed to facilitate a staged cracking. The whole range of pore sizes from micro-pores (< 20 Å) to giant macro-pores (1000 Å) are now known to be influential in determining cracking yield and activity and these pores should be assembled into an optimal architecture. Unfortunately, the configuration of pores in a typical spray dried FCC catalyst is usually far from such an optimal design. The use of stochastic pore networks to characterise macro-pore structures is described in conjunction with some experimental results employing a visualised porosimetry based on low melting point alloy impregnation. Improved designs of catalyst will impose new requirements on the fluidised bed hardware. Some recent improvements in the chemical engineering of riser reactor/regenerator units are described which centre on atomised injection, segregated feeding, closed cyclones, staged stripping and catalyst cooling.     

New route for synthesizing Mn-silicalite-1

Mn-silicalite-1 (Mn_5.2Si_90.8O₁₉₂) was synthesized from Mn²⁺ ion-exchanged magadiite. The characteristics of Mn-silicalite-1 were investigated using electron spin resonance, synchrotron X-ray powder diffraction, IR spectroscopy and chemical analysis. The measurements indicate that Mn²⁺ ions replace Si in the silicalite-1 framework. The orthorhombic framework structure of calcined Mn-silicalite-1 has been determined. The space group is Pnma, with a=20.1017(3) Å, b=19.8826(4) Å, c=13.3758(3) Å.     

Characterization of cancrinite synthesized in 1,3-butanediol by Rietveld analysis of powder neutron diffraction data and solid-state Na NMR spectroscopy

The framework structure and extraframework atoms of calcined and dehydrated cancrinite synthesized in 1,3-butanediol are characterized by powder neutron diffraction and ²³Na nuclear magnetic resonance (NMR) spectroscopy. The cancrinite structure is refined in the hexagonal space group P6₃ (No. 173) with lattice parameters a=12.659 Å and c=5.153 Å. Carbonate anions are found occluded in the pores of the cancrinite structure. Although there are two different crystallographic cation sites found by the Rietveld refinement, there are three peaks in the ²³Na magic-angle spinning (MAS) NMR spectrum. These peaks correspond to sodium cations found in site I inside the cancrinite cages, cations in site II inside the cancrinite pore without neighboring carbonates, and cations in site II with neighboring carbonates. Quadrupole coupling constants (QCC) obtained by a simple point-charge model agree well with the simulation of the ²³Na MAS NMR spectra.