Development of nitride supported catalysts for the hydrogenation and reductive amination of bio-sourced acids – NITAMIN

Molybdenum nitrides were synthesized from MoO3 placed in a quartz cell, in an oven. This material was then heated under a flow of H2/N2, which allow the reduction of the oxide and the incorporation of nitrogen into the structure. Many parameters were varied during the synthesis, in order to understand the formation mechanisms and to optimize the properties of the nitride. The textural and structural properties of these solids were extensively characterized using a wide range of techniques. We were able to couple some of the results obtained with theoretical calculations.
The catalysts were then tested for the hydrogenation of succinic acid, levulinic acid and furfural in liquid phase. These three molecules are biomass-based. These reactions were carried out in a closed reactor, under temperature and H2 pressure. The analysis of the samples over time made it possible to follow the kinetic and to evaluate the catalytic properties of our materials. However, molybdenum nitrides showed some stability issues during their storage. This phenomenon led to problems of reproducibility of the catalytic results.

We developed simple synthesis methods of ß-Mo2N, ?-Mo2N (bulk and supported) materials by TPN of MoO3 (MoO3/support) with 15% v/v N2/H2 at 700 °C. By varying the parameters of synthesis, it is possible to tune the amount of nitrogen and consecutively altered quantity of N-deficient sites within nitride structure. We elucidated, for the first time, that formation mechanisms of both, ß and ?, phases in N2/H2 systems pass through the same intermediate phases including: molybdenum bronze (HxMoO3), MoO2 and Mo. We proved that the determining parameters, temperature rate and GHSV, impact the crystallite size of metallic Mo and the kinetic of the reduction and nitridation. Concentration of N-vacancies in bulk materials can be tuned by varying the GHSV, the final nitridation temperature and MoO3-particle size. Finally, for the first time UPS data were coupled with DFT calculation for molybdenum nitride. We also developed methods for the syntheses of W2N and VN employing NH3 as nitrogen source. The nitrides catalysts were tested for the hydrogenation of biomass derived chemicals. Promising results were obtained for the hydrogenation of furfural to furfuryl alcohol, despite some problem of stability during storage.

This work allowed the development of catalysts based on molybdenum nitride capable of carrying out the catalytic transformation of furfural into furfuryl alcohol, in liquid phase. We developed a simple method for the synthesis of molybdenum nitride, bulk or supported. We demonstrated that it is possible to control the crystallographic phase, as well as other textural properties, by adjusting the synthesis parameters. Preliminary results were also obtained for tungsten and vanadium nitrides.

One article is being submitted, and another one is being written.
The fundamental aspect of the subject did not allow patents to be filed.
Due to the pandemic, several presentations in conferences were cancelled; however, the results were presented at one international and two national conferences.

Heterogeneous catalysis represents a cornerstone of green chemistry. Indeed, catalytic systems can be designed to fulfil the dual demands of environmentally friendly and economically competitive chemical processes. The most effective catalysts for hydrogenation reactions usually contain a noble metal supported on an oxide carrier. However, a review of the literature dealing with the formulation of catalysts reveals a growing interest on the development and use of interstitial nitrides of early transition metals (e.g. Mo, W, V). Compared to noble metal, metal nitrides can be more resistant, have particular chemical stability and exhibit distinct products selectivities which have yet to be fully exploited.

The objective of NITAMIN project is the development of supported metal nitrides as promising non precious alternative to conventional noble metals for reactions of particular interest like hydrogenation and reductive amination of bio-derived carboxylic acids to the corresponding diols or pyrrolidone derivatives, respectively. These compounds are valuable and useful products used as solvents and in the preparation of polymers.

Studies on nitride systems have mainly focused on the synthesis of unsupported molybdenum nitride. For the bulk materials, the adsorption and catalytic properties are governed by bulk structure and surface composition where Mo oxidation state, crystallographic structure, degree of nitridation play a crucial part. Nitride supported catalysts are usually prepared by impregnation followed by reduction and nitridation steps. Recently it has been reported that some of the critical parameters (e.g. nitride dispersion) can be affected by the nature of the support. With this project we want to investigate the influence of synthesis procedure on the catalyst structural characteristics. From the gained knowledge, we will be able to control and tailor the critical properties in order to enhance activity, selectivity and stability.

Characterization will be undertaken in order to gain a better control on the nitridation reaction mechanism and structure/activity relationship. The nature of precursor, the deposition route and the thermal treatment conditions are key parameters to optimise the catalytic response. Along with the traditional impregnation route, alternative methods will be investigated, such as sol-immobilisation. A careful characterization will be undertaken by Raman spectroscopy and XPS in order to identify the critical parameters controlling the selectivity, activity and stability of the catalysts for each reaction. We will focus first on Mo nitride systems and then move on towards W and V nitrides. TiO2, ZrO2 and C will be used as supports, as they are known to be more stable under the harsh conditions encountered during these reactions.

We will also develop a systematic DFT based thermodynamics investigations into the surface energies, morphologies and phase transformations of three metal nitride phases. This will allow us to identify the morphology of the nitrides in function of the preparation conditions and investigate the effect of reaction conditions on them.

N. Perret is specialised in the development of nitride catalysts for hydrogenation reactions. With this project, she will broaden her knowledge in characterisation of solids by working with S. Loridant at IRCELYON, a specialist in oxide materials synthesis and characterisation, especially Raman spectroscopy. This project will also be conducted in collaboration with C. Michel at LC-ENSL, a recognized expert in simulations for biomass conversion. ISA laboratory will also be involved, as they have been developing analytical methods for determining the composition of refractory compounds for the past twenty years. Two postdoc researchers will be hired for this project, with a total of 30 person.months. The total ANR funding requested is 251000€.