http://localhost:8081/jspui/handle/123456789/23 2026-10-23T01:07:21Z 2026-10-23T01:07:21Z Rajput, Akanksha Singh http://localhost:8081/jspui/handle/123456789/21755 2026-10-21T11:14:45Z 2024-12-01T00:00:00Z

Title: Nickel-Ceria Based Catalyst For Syngas Production From Dry Reforming of Methane Authors: Rajput, Akanksha Singh Abstract: The dry reformation of methane (DRM) provides a sustainable method for reducing greenhouse gas emissions by transforming carbon dioxide (CO2) and methane (CH4) into syngas (CO and H2). This thesis investigates the production and catalytic efficacy of Ni-Ce catalysts based on alumina by the sol-gel technique. The main goal was to enhance catalyst efficacy for syngas and multi-walled carbon nanotube (MW-CNTs) manufacturing while tackling prevalent issues including carbon deposition and catalyst deactivation. The synthesized catalysts were comprehensively characterized employing techniques such as Brunauer-Emmett-Teller (BET) surface area analysis, hydrogen temperature-programmed reduction (H2-TPR), carbon dioxide temperature-programmed desorption (CO2-TPD), X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), and Thermogravimetric analysis (TGA). These approaches provide insights into the structural characteristics, reducibility, surface acidity/basicity, crystallinity, and morphological stability of the catalysts. Particular emphasis was placed on the advancement of alumina-supported perovskite-type Ni-Ce catalysts, which demonstrated enhanced resistance to carbon deposition while preserving catalytic activity. Additionally, a regeneration mechanism was created to reinstate catalytic performance post-deactivation, providing a pragmatic method to extend catalyst longevity. The study enhances DRM by offering an in-depth knowledge of Ni-Ce perovskite-type catalysts, with ramifications for greener energy generation and the manufacture of precious carbon nanomaterials.

2024-12-01T00:00:00Z Kumar, Pankaj http://localhost:8081/jspui/handle/123456789/20508 2026-04-24T06:38:15Z 2024-08-01T00:00:00Z

Title: DIRECT HYDROTHERMAL VALORIZATION OF BIOMASS AND ELECTROPLATING EFFLUENT Authors: Kumar, Pankaj Abstract: With the global increase in industrial activities and urban expansion, addressing cleaner energy production and wastewater treatment has become a critical aspect of responsible environmental management. Industrial activities, particularly those involving metal processing, contribute significantly to the carbon dioxide emission and contamination of water bodies with heavy metals, presenting significant environmental hazards and potential threats to human health. Heavy metals such as copper, zinc, cobalt, and nickel are a few of the most widely used metals, mainly in the electroplating and mining industries. Fatal consequences may arise if the trace amounts of these metals in the human body exceed the threshold limits. Therefore, these heavy metals must be recovered from the wastewater streams economically and effectively. Moreover, the energy utilized by heavy metal industries is produced from non-renewable sources (coal and oil), contributing to greenhouse gas emissions. The depletion of fossil fuel reservoirs, coupled with the escalating specter of global warming, prompts researchers to shift their attention toward renewable energy alternatives such as biomass. Biomass is a carbon-neutral and environmentally friendly energy resource with significant economic value and abundant reserves. The biomass's thermochemical conversion route (pyrolysis and gasification) encounters limitations attributed to its elevated moisture content, necessitating substantial energy inputs for the drying process. Supercritical water gasification (SCWG) offers a distinct advantage in effectively handling wet biomass to generate a hydrogen-rich fuel gas mixture. In this, supercritical water (SCW) is utilized as a solvent and reaction medium to transform lignocellulosic biomass into a fuel gas rich in high value H2-rich gaseous fuel and biochar. SCW shows improved heat transfer and mass transfer properties with higher solvation properties. To enhance the performance and yield of hydrogen, catalysts were incorporated into the process under controlled operating conditions during SCWG. However, these catalysts are prone to deactivation during the process. Henceforth, this research highlights the in-situ utilization of metal-contaminated wastewater as a catalyst infused with lignocellulosic biomass for the co-synthesis of a hydrogen-rich fuel gas mixture and nanometal carbon hybrid (NCH) via SCWG.

2024-08-01T00:00:00Z Jain, Neha http://localhost:8081/jspui/handle/123456789/20460 2026-04-20T10:31:04Z 2024-07-01T00:00:00Z

Title: FILM FLOWS INSTABILITIES: EFFECT OF SURFACTANT, IMPOSED SHEAR AND POROUS SUBSTRATE Authors: Jain, Neha Abstract: Cylindrical liquid film flows present inside or outside of a vertical tube or wire is ubiquitous and garnered a lot of interest in literature due to its applications in industrial, technological and biological processes. These film flows are prone to the disturbances where the amplification of the disturbances over time may distort the interfaces and render it unstable. These instabilities may be desirable for enhanc ing the heat and mass transfer phenomena in the distillation unit, heat exchangers, falling film reactors and also for the formation of liquid drops in microfluidic de vices. There are situations where the perfectly cylindrical interfaces are required such as during the coating of wire. The distortions at the interface creates an un even film thickness which affects the final quality of the product. Therefore, many strategies have been developed to control or manipulate these instabilities such as the use of surface-active agents at the gas-liquid or liquid-liquid interfaces, applica tion of an externally imposed shear stress at the free surface, by replacing the rigid solid wall with the soft or deformable solid substrate, etc. Consequently, the stabil ity of these film flows has been an important area of research both experimentally and theoretically. Cylindrical liquid films present inside or outside of a tube always remain unsta ble due to the surface tension driven capillary instability which is termed as the Rayleigh-Plateau (RP) instability. This RP instability exists even in the absence of inertia. However, the presence of inertia excites an another mode of instability at the free surface that is known as free surface instability, which exists for both planar and cylindrical film flows. Furthermore, for the stationary cylindrical film, the effect of the presence of an insoluble surfactant was found to be stabilising. It decreases the growth rate of the Rayleigh-Plateau instability but could not eliminate it completely (Camapana et al. 2004; Carroll & Lucassen 1974; Cassidy et al. 1999; Halpern & Grotberg 1993). However, in the presence of the basic flow, the RP instability was completely eliminated above a critical value of the Marangoni number (Nair & Sharma 2020). They also investigated that the surfactant mode remains stable in the low wavenumber limit and become unstable for a range of arbitrary wavenumber ii for high Marangoni number. Similar observation of complete suppression of RP instability was made by (Ogrosky 2021) for the liquid film present inside of a tube but did not mention anything about finite wavenumber instability as investigated by (Nair & Sharma 2020). Apart from the effect of presence of surfactant at the free surface (passive gas), number of studies are available where the surfactant loaded gas-liquid interface is subjected to an externally applied shear stress for planar and cylindrical film flows. The presence of an imposed shear was found to be destabilis ing or stabilising (downstream or upstream direction) for the gas-liquid mode. The surfactant mode was found to be unstable solely due to the presence of basic shear (Bhat & Samanta 2019; Wei 2005b; Zhou et al. 2014). The existing literature has explored the effect of the surfactant for the liquid film present inside of a tube using lubrication or the long wave approximation. There fore, in one of the objective of this thesis: (1) We investigated the effect of the surfactant on the liquid film present inside of a vertical tube in presence of the base f low using the long-wave and numerical shooting method. Furthermore, to the best of our knowledge no study has examined the effect of the imposed shear stress at the gas-liquid for the liquid film flowing outside of a vertical fibre. Hence, the second objective is: (2) To examine the effect of an imposed shear stress on the stability of gravity-driven surfactant doped Newtonian liquid film flowing outside of a verti cal rod or fibre. Both the studies were conducted in the limit of vanishingly small Reynolds number (Re “ 0). We carried out the linear stability analysis using the long-wave asymptotic analytical method and further extended our results to finite or arbitrary wavenumbers using the numerical shooting method. In Chapter 2 of this thesis, the stability of the gravity-driven and surfactant-doped Newtonian liquid film present inside of a vertical tube was examined using the lin ear stability analysis in the creeping flow limit. This flow configuration exhibits two normal modes of instability. (i) Surface tension-driven Rayleigh-Plateau mode. (ii) Surfactant mode, which arises due to the gradients of surface tension in presence of surfactant. It has been observed that in the presence of the base flow (character ized by Bond number, Bo), the Rayleigh-Plateau instability can be eliminated com pletely, when the Marangoni number increases above a critical value. In contrast, the surfactant mode which was stable for stationary film now remains unstable for any non-zero value of the Marangoni number, when the base flow was included into iii the stability analysis. This surfactant mode instability was observed to endure for f inite or high wavenumber depending on the liquid film thickness and Bond number. It was noted that the maximum growth rate for the surfactant mode become higher than that of the RP mode for a clean film (Ma=0). Therefore, for moderate and high Bond number, the long-wave nature of instability observed for static film shifts to f inite or short wave surfactant mode instability present into the system. Therefore, the presence of surfactant has an overall destabilizing effect on film flows and the long-wave model is not sufficient to determine the overall stability characteristics of such film flows. In chapter 3 of this thesis, the linear stability of gravity-driven flow of a surfactant laden Newtonian liquid film over a rod is examined in creeping flow limit, in the presence of an externally applied shear stress at gas-liquid (GL) interface. The im posed shear can be applied either in a direction assisting the flow (positive shear stress) or opposite to the direction of the gravity-driven flow (negative shear stress). The two instability modes exist for this flow configuration: (i) Rayleigh-Plateau (RP) mode, and (ii) surfactant mode. Earlier studies revealed that, in absence of im posed shear stress, the surfactant can completely suppress the RP instability above a critical value of Marangoni number. With further increase in Marangoni number to sufficiently high values, the surfactant mode becomes unstable. Hence, there ex ists a window in terms of Marangoni number, where the liquid film remains stable. However, in the presence of imposed shear stress at the gas-liquid interface, the dy namics of the liquid film changes significantly and alters the stability characteristics of the film flow. We first examined the problem using the long-wave asymptotic analysis, it was demonstrated that the positive stress has a stabilizing effect on the RP mode in addition to the stabilizing contribution due to the presence of the sur factant and destabilizing impact on the surfactant mode. Therefore, for any physical situation where the surfactant is present in the sufficiently low concentration (small values of Ma), the application of the suitable magnitude of the positive stress can be used to completely suppress the RP instability. The surfactant mode which remains stable in the absence of an external shear, may become unstable, when the magni tude of the positive stress increases above a threshold value (τ ą τc) and remains stable for τ ă τc. Thus, the effect of increasing the positive shear was found to be destabilizing for the surfactant mode, in contrast to the stabilizing effect for the RP iv mode. It is important to note the the critical value of stress above which surfactant mode destabilises is lower in magnitude to the critical stress required for the sta bilisation of the RP mode. Hence, it is not possible to eliminate the RP instability without triggering the surfactant mode instability. Below this critical value of the stress, long-wave RP instability will be present in to the system whereas above τc, the surfactant mode instability occupies the whole region from low to finite wave perturbations for any value of Marangoni number. Therefore, the positive stress is found to have an overall destabilising effect on the system. However, the extension of the results from low to finite or high wavenumber shows the existence of a stable gap in terms of Marangoni number for small values of the imposed shear stress. This stable gap vanishes, when the shear stress increases beyond the critical value required for the destabilisation of the surfactant mode. For the negative imposed shear stress, the low wavenumber results predicts that for the effect of negative shear stress is destabilizing (stabilizing) for RP (surfac tant) mode, when the magnitude of applied stress is lower than a threshold value (τ ă τc “ 4 d). However, the effect of the imposed shear reverses for both modes when τ ą τc. Note that the critical value of the imposed shear remains same for both the RP or surfactant mode unlike in case of positive shear, where critical stress (τc) was different for both the modes. The analysis concerned with the results of negative shear stress shows that with increase in the magnitude of imposed shear, the finite wavenumber perturbations are destabilised and occupies the whole region in Marangoni versus wavenumber plane. Therefore, it results into the change in stability behavior from long-wave (for stress free interface) to finite wavelength dominated instability. Hence, it is not possible to obtain stable flows when magni tude of shear stress is above a certain value in a similar manner as shown for the positive applied stress. In Chapter 4 of this thesis, we conducted the linear stability analysis of gravity driven Newtonian liquid film flow over a porous inclined plane. The flow in the f luid andporouslayer is modelled with Navier Stokes and volume-averaged Navier Stokes (VANS) equation respectively. In this study, three different modes of insta bility was found: surface mode, shear mode and the porous mode. The surface mode is the long-wave instability mode which triggers due to the deformation of the free surface above a critical value of Reynolds number. In regard of the rigid v plane, it has been observed that for the low angle of inclination, the mode which be come unstable at finite wavenumber was termed as shear or hard mode. However, the porous mode is observed only in the presence of permeable porous substrate instead of rigid plane. The porous mode instability occurs as a results of perme ation of the fluid flow perturbations inside the porous region. We re-examined the research conducted by Camporeale et al. (2013) and made corrections in the pertur bation equations that was initially done by Camporeale et al. (2013). They missed many terms in the boundary condition at the fluid-solid interface (normal stress bal ance) and added an extra term in fourth order ODE for porous layer. It has been observed that the corrected equations significantly change the stability features for the range of parameters typically for large δ. Camporeale et al. (2013) observed that the high wave number porous mode exists with surface and shear for all chosen value of angle of inclination θ. However, such porous mode instability remains ab sent in our analysis. We observed that porous mode do exists but in the range low to finite wavenumber for very small angle 0.03˝ at δ “ 0.02. We also studied the effect of different parameter (d,δ,α,Re,θ) on the flow stability behaviour of the system.

2024-07-01T00:00:00Z Pandey, Akansha http://localhost:8081/jspui/handle/123456789/20442 2026-04-20T06:31:30Z 2024-07-01T00:00:00Z

Title: TRI- REFORMING OF METHANE FOR THE PRODUCTION OF SYNTHESIS GAS Authors: Pandey, Akansha Abstract: The conversion of the two most problematic gases, i.e., CO2 and CH4, to the valuable synthesis gas via the tri-reforming (TRM) is a very promising route. The TRM with CO2, H2O, and O2 to produce synthesis gas (syngas) with an H2/CO molal ratio of 1.5-2 is highly desirable for the production of important chemicals and fuel additives, including methanol, dimethyl ether (DME), and substitute natural gas (SNG), etc., via the Fischer-Tropsch (F-T) process. In this thesis, a novel nano-nickel metal catalyst dispersed on mesoporous-zirconia is developed for the controlled production of the synthesis gas with an H2/CO mol ratio of 1.5-2 via the TRM. The catalysts were tested in a downflow-fixedbed reactor at 600-850 oC and 1 atm. At the optimum feed (CH4:CO2:O2:H2O:N2) ratio of 1: 0.5: 0.1: 0.0125:1, the maximum CO2 and CH4 conversion was ~28% and ~86%, respectively, over the 5 wt.% Ni/ZrO2. At this condition, the syngas with an H2/CO ratio of ~1.5 was obtained at a lower reaction temperature of 700 oC. The superior activity of this catalyst was due to the presence of highly dispersed and reduced nickel particles over the combined tetragonal and monoclinic phases of mesoporous ZrO2. The basic strength of the catalyst, the nickel particle size, and metal dispersion played a important role in controlling the TRM activity as well as the H2/CO mole ratio. The time-on-stream (TOS) study and the used catalyst characterization results established that the nanosized nickel metal particles dispersed on mesoporous-zirconia were thermally stable and coke-resistant. Further, a series of Zr-MOF were synthesized via the solvothermal method, and an impregnation technique was used to synthesize the nickel impregnated on a MOF-derived ZrO2 catalyst. The catalyst was characterized by various methods, including N2-porosimetry, X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), temperature programmed reduction (TPR), H2-chemisorption, CO2-temperature programmed desorption (CO2-TPD), high-resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy (FE SEM), etc. Characterization results supported the formation of the Zr-MOF and nickel metal dispersed on MOF-derived ZrO2. Further, the TRM activity of the catalyst developed were tested in a downflow-fixed bed reactor. The various catalysts were screened for TRM activity at different temperatures (600-850 oC). Results demonstrated that TRM was highly favorable over the NZ-1000 catalyst due to its desirable physicochemical properties, including nickel metal surface area (2.3 i m2.gcat-1), metal dispersion (7.1%), and nickel metal reducibility (45%), respectively. Over the NZ 1000 catalyst, an optimum H2/CO ratio of ~1.6-2 was achieved at 750 °C, and it was stable for a longer period of time. To understand the kinetic behavior of TRM reaction, the kinetic study was performed over 5 wt.% Ni/ZrO2 catalyst under steady-state condition. The reaction temperature and W/FAo were varied from 650-800 oC and 0.61-3.06 g.min.mol-1 at 1 atm. pressure. The Power law model and Langmuir Hinshelwood-Hougen-Watson (LHHW) model for heterogeneous reaction was proposed. The model equations were solved by using MATLAB. For the Power law model, the calculated activation energy with respect to CH4 and CO2 was 42.31 and 83.31 kJ.mol-1, respectively. For the LHHW model, the POM reaction was not considered due to the complete consumption of O2 during the reaction. Therefore, DRM, SRM, and WGS reaction were used for kinetic study. For deriving the rate expression, the surface reaction was considered as the rate-controlling and irreversible in nature. The rate expressions were solved by an ode23 solver in MATLAB in combination with the genetic algorithm optimization tools for the estimation of kinetic parameters. The obtained activation energy for DRM, SRM, and WGS reaction were 76.29, 117.16, and 67.33 kJ.mol-1, respectively.

2024-07-01T00:00:00Z