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The TNU-9 zeolite (TUN framework) is one of the most complex zeolites known. It represents a highly promising matrix for both acid and redox catalytic reactions. We present here a newly developed approach involving the use of 29Si and 27Al (3Q) MAS NMR spectroscopy, CoII as probes monitored by UV/Vis and FTIR spectroscopy, and extensive periodic DFT calculations, including molecular dynamics, to investigating the aluminum distribution in the TUN framework and the location of aluminum pairs and divalent cations in extra-framework cationic positions. Our study reveals that 40 and 60 % of aluminum atoms in the TNU-9 zeolite are isolated single aluminum atoms and aluminum pairs, respectively. The aluminum pairs are present in two types of six-membered rings forming the corresponding α and β (15 and 85 %, respectively, of aluminum pairs) sites of bare divalent cations. The α site is located on the TUN straight channel wall and it connects two channel intersections. The suggested near-planar β site is present at the channel intersection. [ABSTRACT FROM AUTHOR]

The efficiency of catalysts for abatement of emissions of nitrogen oxides (NO x ) from stationary and especially mobile sources using selective catalytic reduction (SCR) is obviously still not sufficient to meet increasingly more stringent environmental limits. We demonstrate that the conversion of NO x to nitrogen under the relevant conditions of the SCR-NO x can be dramatically increased using Al-rich beta zeolite catalysts with a high concentration of transition metal counter-ions, bearing extra-framework oxygen ligand (M/M-oxo, where M = Cu, Co, Fe), particularly in the low-temperature region as well as at high space velocities. The high concentration of framework Al and corresponding high population of AlSiAl sequences in template-free synthesized Al-rich beta zeolite does not result in relative increased binding of bare non-reducible and non-active M(II) ions. To the contrary, the unparalleled high concentration of the atomically dispersed M/M-oxo counter-ions with appropriate redox properties and enhanced specific activities provides 3–12 times higher reaction rates for the SCR-NO x using ammonia, methane and propane as reducing agents compared to state-of-the-art Si-rich zeolite catalysts. [ABSTRACT FROM AUTHOR]

An Al-rich Co-BEA ∗ zeolite (Si/Al 4.2, Co/Al 0.5) was prepared by organotemplate-free hydrothermal synthesis and [Co(II)(H 2 O) 6 ] 2+ ion exchange. The structure of the Co species and their activity in C 3 H 8 –SCR-NO x were compared to that of Si-rich Co-BEA ∗ (Si/Al 11.3). The high population of AlSiAl sequences in Al-rich BEA ∗ with AlO 4 − facing different channels, contrary to their absence in Si-rich BEA ∗ , results in dehydrated Co-BEA ∗ in easily reducible counter-ion [Co(III)O] + species attached to one AlO 4 − . The high concentration and density of these Co-oxo species in Al-rich Co-BEA ∗ facilitates extra-ordinarily high SCR-NO x rate even under water vapor up to 10 vol.%, twelve-times outperforming Si-rich Co-BEA ∗ . The five-to-six times increased TOF and easier reducibility suggest a synergetic redox effect of water-resistant Co-oxo species. The Al-rich Co-BEA ∗ provides the highest reaction rate at conditions of wet NO x streams, exceeding that previously reported for metal ion/oxo zeolite catalysts, with a high selectivity to molecular nitrogen and efficient utilization of propane. [ABSTRACT FROM AUTHOR]

Al-rich template-free BEA * zeolite (Si/Al 4.6) was synthesized and its structure was analyzed in comparison with the conventional H-BEA * zeolite of Si/Al 11.3 using XRD, N 2 sorption, SEM, FTIR, 27 Al 3Q and 29 Si MAS NMR spectroscopy, and DFT calculation of the deprotonation energies. The Al-rich H-BEA * exhibited a high concentration of Brønsted and Lewis sites, both of high acid strength, although AlSiAl sequences were present in the framework. In Al-rich Fe-BEA * the exchanged Fe ions, Fe–oxo species, and Fe–oxo oligomers were identified by UV–vis spectroscopy. Cracking of n -decane, alkylation of benzene with benzyl alcohol and hydroamination of styrene with aniline to ( anti )Markovnikov phenyl-[2-phenylethyl]amine over H-BEA * , and decomposition of N 2 O and NH 3 -SCR-NO x over Fe-BEA * were investigated in relation to the concentration and nature of acid and Fe-redox sites. The high concentration of Al-related active sites and the highly regular structure of Al-rich beta zeolite are directly manifested in enhanced activity compared with conventional Si-rich beta zeolite. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ratio of Al pairs and single Al atoms in zeolites can be tuned in a wide range. [•] Corresponding local negative charges balance bare divalent cations or metal-oxo species. [•] These cation/metal-oxo species control the activity in N2O and NOx related reactions. [ABSTRACT FROM AUTHOR]

Abstract: New type of redox heterogeneous catalysts based on geopolymer aluminosilicate materials was developed and their catalytic properties have been demonstrated on industrially important reactions. Geopolymers can be regarded as amorphous analogues of zeolitic materials (three dimensional network of SiO4 and AlO4 tetrahedra with negative charge of the network balanced by extra-framework cations, variability in chemical composition, ion exchange properties, presence of rings forming cationic sites for bare cations), but possessing some advantages as network formation at ambient or low temperatures, mesoporosity and low cost preparation. It is shown that the geopolymer network enables incorporation of transition metal ions as active centres for catalytic reactions. The catalytic activity of geopolymer-based catalysts with Fe, Co and Cu metal ions in extra-network sites and Pt species is demonstrated on the selective catalytic reduction of nitrogen oxides by ammonia and the total oxidation of volatile hydrocarbons. These findings open a potential for synthesis of new types of robust catalysts for heterogeneously catalysed reactions. [Copyright &y& Elsevier]