The production of biodiesel is greatly increasing due to its enviromental benefits However, production costs are still rather high, compared to petroleum-based diesel fuel The introduction of a solid heterogeneous catalyst in biodiesel production could reduce its price, becoming competitive with diesel also from a financial point of view Therefore, great research efforts have been underway recently to find the right catalysts This paper will be concerned with reviewing acid and basic heterogeneous catalyst performances for biodiesel production, examining both scientific and patent literature

Heterogeneous catalysts for biodiesel production

Zeolites and related crystalline microporous oxides—tetrahedrally coordinated atoms covalently linked into a porous framework—are of interest for applications ranging from catalysis to adsorption and ion-exchange1. In some of these materials (such as zeolite rho) adsorbates2, ion-exchange, and dehydration and cation relocation3,4 can induce strong framework deformations. Similar framework flexibility has to date not been seen in mixed octahedral/tetrahedral microporous framework materials, a newer and rapidly expanding class of molecular sieves5,6,7,8,9,10,11,12,13,14,15,16. Here we show that the framework of the titanium silicate ETS-4, the first member of this class of materials8, can be systematically contracted through dehydration at elevated temperatures to ‘tune’ the effective size of the pores giving access to the interior of the crystal. We show that this so-called ‘molecular gate’ effect can be used to tailor the adsorption properties of the materials to give size-selective adsorbents17 suitable for commercially important separations of gas mixtures of molecules with similar size in the 4.0 to 3.0 A range, such as that of N2/CH4, Ar/O2 and N2/O2.

A titanosilicate molecular sieve with adjustable pores for size-selective adsorption of molecules

This critical review describes the reactivity of heterogeneous catalysts from the point of view of four simple, but essential for Chemistry, molecules (namely dihydrogen, carbon monoxide, nitrogen monoxide and ethylene) that are considered as probes or as reactants in combination with “in situ” controlled temperature and pressure Infrared spectroscopy. The fundamental properties of H2, CO, NO and C2H4 are shortly described in order to justify their different behaviour in respect of isolated sites in different environments, extended surfaces, clusters, crystalline or amorphous materials. The description is given by considering some “key studies” and trying to evidence similarities and differences among surfaces and probes (572 references).

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Probing the surfaces of heterogeneous catalysts by in situ IR spectroscopy

The protein p27Kip1 is an inhibitor of cell division. An increase in p27 causes proliferating cells to exit from the cell cycle, and a decrease in p27 is necessary for quiescent cells to resume division. Abnormally low amounts of p27 are associated with pathological states of excessive cell proliferation, especially cancers. In normal and tumour cells, p27 is regulated primarily at the level of translation and protein turnover. Phosphorylation of p27 on threonine 187 (T187) by cyclin-dependent kinase 2 (Cdk2) is thought to initiate the major pathway for p27 proteolysis. To critically test the importance of this pathway in vivo, we replaced the murine p27 gene with one that encoded alanine instead of threonine at position 187 (p27T187A). Here we show that cells expressing p27T187A were unable to downregulate p27 during the S and G2 phases of the cell cycle, but that this had a surprisingly modest effect on cell proliferation both in vitro and in vivo. Our efforts to explain this unexpected result led to the discovery of a second proteolytic pathway for controlling p27, one that is activated by mitogens and degrades p27 exclusively during G1.

A mouse knock-in model exposes sequential proteolytic pathways that regulate p27Kip1 in G1 and S phase.

Stable microporous materials, such as zeolites, are extremely important for applications in catalysis, adsorption, ion-exchange, and separation. In this review we describe a new class of stable microporous materials that involves novel mixed octhaedral-tetrahedral framework oxides. The archetypal material is based on titanosilicates, although there is tremendous scope for introducing many other transition metals. These materials not only have potential novel applications in the fields normally associated with zeolites but also possible applications in the areas of optoelectronics, nonlinear optics, batteries, magnetic materials and sensors.

Microporous Titanosilicates and other Novel Mixed Octahedral‐Tetrahedral Framework Oxides

The structure of a microporous titanosilicate, ETS-10, has been solved using a combination of electron microscopy, X-ray and electron diffraction, solid-state NMR and distance-least squares analysis. We describe in detail how these tools have been applied to the structural solution. ETS-10 is a highly disordered, yet crystalline, wide-pore microporous framework material containing octahedrally coordinated titanium and tetrahedrally coordinated silicon. The disordered material can be described with respect to two ordered polymorphs: polymorph A, space group P41 or P43 with a = b = 14·8 A and α = β = γ = 90° polymorph B, space group C2/c with a = b = 21·00 A, c= 14·51 A and α = γ = 90°, β= 111·12°. Both polymorphs have'a three-dimensional 12-ring pore system and polymorph A has a spiral channel.

P. J. O. Malley

Papers

Microporous titanosilicate ETS-10: A structural survey