Arunabha Datta

Aqueous phase reforming of glycerol to 1,2-propanediol over Pt-nanoparticles supported on hydrotalcite in the absence of hydrogen

Pt-nanoparticles, in the range of 2–5 nm, supported on hydrotalcite (HT), were used as a catalyst for the selective hydrogenolysis of glycerol to produce 1,2-propanediol by aqueous phase reforming in the absence of any added hydrogen. The catalyst was characterized by XRD, N2-sorption, pulse chemisorption, TPR, XPS, SEM, TEM, EXAFS. The influence of reaction parameters like reaction time, pressure, etc., were studied in detail. The study reveals that the Pt-nanoparticles are the active sites for the selective conversion of glycerol to 1,2-propanediol. The role of the support also plays an important role in the hydrogenolysis. The hydrogen required for the hydrogenolysis is derived from the reforming of H2O over the Pt-HT catalyst. The mechanism of the hydrogenolysis reaction is also proposed. A glycerol conversion of 98% with a 1,2-propanediol selectivity of 74% was achieved over 3 wt% Pt supported on HT. The reusability of the catalyst was tested by conducting four runs with the same catalyst and it was found that after four reuses, the conversion and selectivity was almost same.

Characterization and catalytic activity of novel palladium-incorporated vanadium phosphates

Abstract Palladium has been introduced into the layered vanadyl hydrogen phosphate hemihydrate VOHPO4·0.5H2O in different ways depending upon the medium of preparation. In aqueous medium, the introduction of palladium leads to the formation of a new phase containing mixed valent vanadium whereas in the preparation in organic medium, the palladium appears to substitute into the lattice of the parent compound. The palladium-incorporated compounds have been found to be catalytically active, both for oxidative coupling as well as for hydrogenation reactions, with the activity and selectivity varying quite markedly with the mode of incorporation.

A novel procedure for the synthesis of NH3 incorporated VPO phases

It has been observed that as a function of a time delay introduced between the onset of the reduction of V2O5 with hydroxylamine hydrochloride and the addition of phosphoric acid, in the aqueous route preparation of the catalytically important VOHPO4·0.5H2O phase, a series of NH3 incorporated phases are obtained. Up to delay times of 3 min the crystalline VOHPO4·0.5H2O phase is obtained whereas a weakly crystalline hemihydrate is formed at a delay time of 4 min. Longer delay times result in X-ray amorphous phases until at delay time of 10 min and above a new crystalline phase containing mixed-valent vanadium emerges. All the phases obtained with delay times of 4 min and above have NH3 incorporated into them. The weakly crystalline VOHPO4·0.5H2O phase as well as the X-ray amorphous phases undergo transformation to a crystalline vanadyl pyrophosphate phase on calcination at 723 K in spite of having NH3 incorporated into them. The in-situ generation of NH3 during the preparation procedure is a hitherto unreported aspect of VPO chemistry and provides a convenient method for the preparation of novel NH3 incorporated VPO phases which could have strong potential as catalysts for alkane oxidation as well as for ammoxidation reactions.

Novel platinum incorporated vanadium phosphates and their catalytic activity

Abstract Platinum has been incorporated into the layered vanadyl hydrogen phosphate VOHPO 4 ·0.5H 2 O in different ways depending upon the medium of its preparation. The phase obtained by the introduction of platinum during the synthesis of VOHPO 4 ·0.5H 2 O in aqueous medium is a new crystalline phase with mixed-valent vanadium containing Pt 2+ species. This phase forms a novel hydrogen insertion compound involving hydrogen spillover from the incorporated platinum onto the VPO matrix. On the other hand, the incorporation of platinum during the synthesis of the hemihydrate in organic medium gives rise to a phase containing both metallic platinum and an amorphous Pt 2+ containing VPO phase. Both these platinum incorporated phases have been found to be active catalysts for reduction and oxidation reactions such as the hydrogenation of nitrobenzene and the oxidation of tetrahydrofuran with the activity varying quite markedly with the mode of incorporation.

Novel vanadium phosphate phases as catalysts for selective oxidation

In our effort to induce novel modifications in the structure of some important vanadium phosphate phases used as selective oxidation catalysts, it has been observed that metal ions such as Zn2+, Ni2+, Pd2+can be incorporated into the vanadyl hydrogen phosphate VOHPO40.5H2O phase in very different ways depending upon the medium of preparation. It has been found that the metal ions are either substituted into the lattice with retention of structure of the parent compound or intercalated between the layers of a new mixed-valent phase. These new metal-incorporated phases are catalytically active and the palladium incorporated compound in particular displays shape selective catalysis for different oxidation and reduction reactions. In another approach, the preparation of VOHPO40.5H2O) has been modified to give a novel crystalline phase containing mixed-valentvanadium and having NH3 species bound to the lattice. This phase could be a potential catalyst for ammoxidation reactions. In addition, novel mesostructured vanadium phosphate phases have been prepared using a long-chain amine as the templating agent involving a ligand templating mechanism of formation.

Novel compounds of nickel intercalated/substituted into the vanadyl orthophosphate VOHPO4·0.5H2O and their catalytic activity

Nickel incorporated into the vanadyl orthophosphate VOHPO4·0.5H2O appears to intercalate in aqueous medium and substitute into the lattice of the parent compound in organic medium; these nickel compounds show different catalytic activity.

Characterization and catalytic activity of palladium dispersed on Kratschmer–Huffman (K–H) soot

Palladium dispersed on K–H soot, both before and after extraction with solvents, is shown to exist in a range of oxidation states and is an active catalyst for the disproportionation of cinnamyl alcohol to cinnamaldehyde and dihydrocinnamyl alcohol under condition where a commercial Pd/C catalyst is inactive.

Metal ion incorporated VPO phases as novel catalysts

Vanadium phosphates function as catalysts for the selective oxidation of hydrocarbons with their activity being strongly dependent on their structure. Consequently, attempts have been made to synthesise novel phases in the VPO system through metal ion incorporation and evaluate the catalytic activity of these phases. It is shown that the incorporation of palladium or platinum leads to novel phases which vary according to the method of syntheses. The incorporated metal ions are catalytically active both for oxidation and reduction reactions with the activity varying according to the mode of incorporation. These phases constitute a novel class of compounds in which oxidation centres are substituted or dispersed within a VPO oxidation catalyst.

NOVEL MODIFICATIONS OF THE STRUCTURE OF THE LAYERED VANADYL HYDROGENPHOSPHATE VO(HPO4).0.5H2O

The addition of metal ions such as Zn2+, Ni2+ and Pd2+ during the preparation of the layered vanadyl hydrogenphosphate VO(HPO4)·0.5H2O in aqueous media led to the formation of a new phase which is very different from that of the parent compound. This phase, which appears to be structurally similar to the vanadium(V) phosphate VO(PO4)·2H2O, is a mixed-valent vanadium compound with an expanded c-axis spacing in which the incorporated metal ions, in their divalent state, appear to be lodged in the interlayer region.

Evidence for a hydrogen insertion compound of novel palladium incorporated vanadyl hydrogen phosphates

Palladium is shown to be incorporated into the vanadyl hydrogen phosphate phase VOHPO4·0.5H2O in different ways depending on the medium used for preparation; temperature programmed reduction (TPR) studies provide evidence for the formation of a hydrogen insertion compound of one of these palladium incorporated vanadyl phosphates.