The infrared spectral performance of the N x O y species observed on oxide surfaces [N2O, NO−, NO, (NO)2, N2O3, NO+, NO2 − (different nitro and nitrito anions), NO2, N2O4, N2O5, NO2, and NO3 − (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N2, H-, and C-containing nitrogen oxo species, C─N species, NH x species) are also briefly discussed. Some guidelines for spectral identification of N x O y adspecies are proposed and the transformation of the nitrogen oxo species on catalyst surfaces are regarded.

Identification of Neutral and Charged N x O y Surface Species by IR Spectroscopy

The development of new, sustainable, low-CO2 construction materials is essential if the global construction industry is to reduce the environmental footprint of its activities, which is incurred particularly through the production of Portland cement. One type of non-Portland cement that is attracting particular attention is based on alkali-aluminosilicate chemistry, including the class of binders that have become known as geopolymers. These materials offer technical properties comparable to those of Portland cement, but with a much lower CO2 footprint and with the potential for performance advantages over traditional cements in certain niche applications. This review discusses the synthesis of alkali-activated binders from blast furnace slag, calcined clay (metakaolin), and fly ash, including analysis of the chemical reaction mechanisms and binder phase assemblages that control the early-age and hardened properties of these materials, in particular initial setting and long-term durability. Perspectives fo...

Geopolymers and Related Alkali-Activated Materials

Focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides. Characterization of the molecular structures of chromium; Mechanics of hydrogenation-dehydrogenation reactions; Mobility and reactivity on oxidic surfaces.

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Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides.

This paper presents a review of alkali-activation technology, moving from the atomic scale and chemical reaction path modelling, towards macroscopic observables such as strength and durability of alkali-activated concretes. These properties and length scales are intrinsically interlinked, and so the chemistry of both low-calcium (‘geopolymer’) and high-calcium (blast furnace slag-derived) alkali-activated binders can be used as a starting point from which certain engineering properties may be discussed and explained. These types of materials differ in chemistry, binder properties, chemical structure and microstructure, and this leads to the specific material properties of each type of binder. The secondary binder products formed during alkali-activation (zeolites in low-Ca systems, mostly layered double hydroxides in alkali-activated slags) are of significant importance in determining the final properties of the materials, particularly in the context of durability. The production of highly durable concretes must remain the fundamental aim of research and development in the area of alkali-activation. However, to enable the term ‘highly durable’ to be defined in a satisfactory way, the underlying mechanisms of degradation—which are not always the same for alkali-activated binders as for Portland cement-based binders, and cannot always be tested in precisely the same ways—need to be further analysed and understood. The process of reviewing a topic such as this will inevitably raise just as many questions as answers, and it is the intention of this paper to present both, in appropriate context.

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Geopolymers and other alkali activated materials: why, how, and what?

Fly ash-based geopolymer: clean production, properties and applications

Determination and properties of acid sites in H-ferrierite: A comparison of ferrierite and MFI structures

Geopolymer based catalysts—New group of catalytic materials

Ion exchange of Na+ ions in a geopolymer by Cs+, NH4+, and Co2+ was used to characterize the accessibility of the inner volume of a Na-geopolymer (Si/Al 1.8) and the size of the rings controlling the mobility of cations in the geopolymer matrix. Ultraviolet (UV)—visible (vis) spectroscopy of Co2+ ions in the Co2+-exchanged geopolymer was used to characterize the local geometry of the Co2+ ions and the regularity and shape of local structures accommodating these Co2+ ions in the geopolymer matrix. Na-geopolymers exhibit ion-exchange properties similar to those of zeolites. All Na+ ions balancing Al atoms of the network of the as-prepared geopolymer could be replaced (ion-exchanged) by NH4+ or Co2+ ions. By analogy to zeolites, this indicates that all the Al atoms are accessible through rings containing at least eight Al and Si atoms. Co2+ ions in the geopolymer network are accommodated in two regular types of deformed six-membered or eight-membered rings. As indicated by the lower extent of Cs+ exchange, only one-half of the Al atoms are simultaneously accessible through 10-membered or larger rings. This indicates that neither regular alumosilicate six-membered rings nor the hexagonal prisms typical of some zeolitic structures are present in the geopolymer network.

Metal Ions as Probes for Characterization of Geopolymer Materials

Local lattice perturbation induced by bonding of a single cobalt ion at cationic sites in dehydrated CoH–beta zeolite (Si/Al 11.5–12.2, Co/Al 0.06–0.4) decreases after cobalt interaction with basic molecules, i.e. C 2 H 4 , C 2 H 5 NH 2 , NH 3 , and CD 3 CN. Lattice perturbation is manifested by a reverse change of an IR band at the transmission window region for a bare cation at 916 cm −1 , giving a relaxation shift for the 1 : 1 complex, Δ r , equal to 10–26 cm −1 . The order of Δ r values was as follows: C 2 H 5 NH 2  ≅ CD 3 CN > NH 3  ⪢ C 2 H 4 . The value of the ‘relaxation shift’ correlates well with the strength of the cobalt–ligand bonding in Co–adsorbate complexes. It has been found that during the desorption experiment on CoH–BEA of Co/Al > 0.2 at temperatures above 300°C, the Co–ethylamine is converted into the Co–acetonitrile complex without oxygen present in the gas phase. This transformation occurs on the single Co ions and is not connected with non-specified Co oxidic species present in some highly Co-loaded CoH–beta zeolites.

Zdenka Tvarůžková

Papers

Determination and properties of acid sites in H-ferrierite: A comparison of ferrierite and MFI structures

Geopolymer based catalysts—New group of catalytic materials

Metal Ions as Probes for Characterization of Geopolymer Materials

Metal ligand complexes in CoH-BEA relevant to ethane ammoxidation to acetonitrile : an FTIR study

Monitoring of skeletal T–O–T vibrations of metal ion exchanged zeolites: An attempt at quantitative evaluation