Nadadur Veeraraghavan Srinath

Bio: Nadadur Veeraraghavan Srinath is an academic researcher from Ghent University. The author has contributed to research in topics: Catalysis & Dehydrogenation. The author has an hindex of 3, co-authored 6 publications receiving 21 citations.

What Makes Fe-Modified MgAl2O4 an Active Catalyst Support? Insight from X-ray Raman Scattering

Abstract: Fe-modified MgAl2O4 makes a surprisingly active catalyst support, likely linked to a structural effect of the Fe incorporation. Two catalyst supports, MgAl2O4 and MgFeAlO4, have been studied in fre...

Looking inside a Ni-Fe/MgAl2O4 catalyst for methane dry reforming via Mössbauer spectroscopy and in situ QXAS

Abstract: The evolution of the constituents of an 8 wt%Ni-5 wt%Fe/MgAl2O4 catalyst for dry reforming of methane (DRM) is monitored by in situ quick X-ray absorption spectroscopy (QXAS) and 57Fe Mossbauer spectroscopy. In as prepared state, Fe is present as NiFe2O4 at the surface and as MgFe3+xAl2−xO4 within the support, whereas Ni is mainly present as NiO. During H2-TPR, NiFe2O4 and NiO form an alloy from 500 °C on and MgFe3+xAl2−xO4 is partially reduced to MgFe2+xAl2−xO4, such that Ni-Fe alloy, MgFe2+xAl2−xO4 and MgFe3+xAl2−xO4 are the prevalent phases in the reduced catalyst. During DRM, dominantly oxidizing environments (CH4/CO2 = 1/2, 1/1.5) lead to formation of FeOx nanoparticles at the surface of the Ni-Fe alloy, thereby affecting the DRM activity, and possibly to some reincorporation of Fe into the support. For CH4/CO2 = 1/1, no significant changes occur in the catalyst’s activated state, as a consequence of reduction by CH4 dissociation species counteracting oxidation by CO2. However, Mossbauer analysis detects continued extraction of Fe from the support, sustaining ongoing Ni-Fe alloying.

In Situ XAS/SAXS Study of Al2O3-Coated PtGa Catalysts for Propane Dehydrogenation

Abstract: The effects of applying an alumina (Al2O3) coating by atomic layer deposition, with a thickness of about similar to 1 nm, on two PtGa catalysts (PtGa/MgAl2O4 and Pt/MgGaAlO) were explored for the propane dehydrogenation reaction (PDH). The combined application of small angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) was employed on the samples to gain insight into the effect of this coating on catalyst stability. The coating restricted the mobility of surface metal nanoparticles, thereby preventing sintering of the catalyst. On the PtGa/MgAl2O4 catalyst, the presence of the coating hindered the alloy formation between Pt and Ga, while it did not negatively affect the formation of an alloy for the Pt/MgGaAlO catalyst as the Ga is delivered from the support. The SAXS and XAS findings were reflected in the PDH activity tests. The alumina-coated PtGa/MgAl2O4 performed worse than its uncoated counterpart due to the limited alloy formation in the presence of the coating. The coated and uncoated Pt/MgGaAlO catalysts were tested for PDH after 1, 5, and 10 H-2/O-2 redox cycles to see the effect of the coating on activity and stability. In general, the coating reduces the total amount of carbon formation, and the rate of deactivation for the coated sample is slower than for the uncoated counterpart. A higher thickness of coating led to reduced activity due to increased blockage of active sites but at the same time drastically reduced total carbon formation at similar conversions. The coated and uncoated Pt/MgGaAlO samples were then subjected to another 30 redox cycles (40 in total) and subsequently examined with HAADF STEM. Through particle size distribution of STEM images, it is determined that the coating reduced the extent of sintering of the sample. The direct correlation between increased coating thickness and lower extent of sintering of the surface metal nanoparticles was confirmed.

Partial positively charged Pt in Pt/MgAl2O4 for enhanced dehydrogenation activity

Abstract: Platinum group metals hold pronounced potential for the dehydrogenation process of liquid organic hydrogen carriers (LOHCs) such as decalin, but the strong adsorption of dehydrogenation product has suppressed the moving forward of these catalysts. Herein, we described that the strong interactions between Pt and MgAl2O4 trigger partial positively charged Pt, which mitigates the adsorption of naphthalene on highly active Pt sites, thus achieving an outstanding decalin dehydrogenation activity that is nearly twice that of state-of-the-art Pt/CNF catalysts. As revealed by various characterization outcomes and DFT calculations, the strong electronic interactions between Pt and spinel oxygen surface resulted in partial positively charged Pt on MgAl2O4, which inhibits the electron transfer from Pt to unsaturated carbon of naphthalene, thus weakening the bond strength between Pt and naphthalene. As a result, the combination of small-sized Pt nanoparticles and facile desorption of products endows tremendous dehydrogenation activity of Pt/MgAl2O4. This study may shed new light on the rational construction of highly efficient metal catalysts for the application of LOHCs.

Light olefin synthesis from a diversity of renewable and fossil feedstocks: state-of the-art and outlook.

Abstract: Light olefins are important feedstocks and platform molecules for the chemical industry. Their synthesis has been a research priority in both academia and industry. There are many different approaches to the synthesis of these compounds, which differ by the choice of raw materials, catalysts and reaction conditions. The goals of this review are to highlight the most recent trends in light olefin synthesis and to perform a comparative analysis of different synthetic routes using several quantitative characteristics: selectivity, productivity, severity of operating conditions, stability, technological maturity and sustainability. Traditionally, on an industrial scale, the cracking of oil fractions has been used to produce light olefins. Methanol-to-olefins, alkane direct or oxidative dehydrogenation technologies have great potential in the short term and have already reached scientific and technological maturities. Major progress should be made in the field of methanol-mediated CO and CO2 direct hydrogenation to light olefins. The electrocatalytic reduction of CO2 to light olefins is a very attractive process in the long run due to the low reaction temperature and possible use of sustainable electricity. The application of modern concepts such as electricity-driven process intensification, looping, CO2 management and nanoscale catalyst design should lead in the near future to more environmentally friendly, energy efficient and selective large-scale technologies for light olefin synthesis.

Oxygen defective bimodal porous Ni-CeO2−x-MgO-Al2O3 catalyst with multi-void spherical structure for CO2 reforming of CH4

Abstract: Ni-CeO 2 -MgO-Al 2 O 3 catalysts with bimodal meso-macropores have been synthesized by one-pot spray pyrolysis using dextrin as a structuring agent for dry reforming of methane. The formation of macropores originating from phase segregation and the decomposition of dextrin positively affects both the physical and chemical features of the catalysts, and therefore, the bimodal porous catalysts outperform the dense catalysts in catalytic activity and stability. The volume and size of macropores in a bimodal porous catalyst are dependent on the concentration of dextrin. Based on diverse characterization results, this morphological change has been revealed to induce the distortion of the CeO 2 lattice and embedding of Ni nanoparticles, resulting in the strong interaction between the metal and support/promoter and high oxygen storage capacity. The catalyst with balanced bimodal pore structures and optimized physicochemical parameters showed the best performance, considering both catalytic activity and stability with high sintering/coking resistance in the dry reforming of methane. Morphological changes by dextrin addition have been revealed to induce the distortion of the CeO 2 lattice and embedding of Ni nanoparticles, resulting in catalytic stability of the catalyst for DRM. • The hierarchical porous catalyst was synthesized by spray pyrolysis using dextrin. • The volume of the macropores was controlled by the concentration of dextrin. • This morphological change induced distortion of CeO 2 lattice and embedding of Ni. • The distortion of CeO 2 lattice and embedding of Ni result to the high OSC and SMSI. • The optimized catalyst showed stable activity with high sintering/coke resistance.