Hydrogen has a potential to be a clean energy carrier that emits only water after combustion and can be produced from diverse feedstocks. Hydrogen has much better combustion characteristics in conventional combustion systems and higher energy efficiency when used with fuel cells. More than 75 million tons of hydrogen are currently produced primarily using fossil fuels as feedstock via steam methane reforming processes. Steam methane reforming is the mature technology for producing hydrogen and when coupled with CO2 capture can help address climate challenges. Inorganic palladium (Pd) membranes have demonstrated great potential to separate hydrogen due to their stability and high selectivity for hydrogen. In this review, several methods of fabricating Pd-alloy membranes are discussed and compared in terms of membrane stability and selectivity of hydrogen. Such methods include electroless plating (ELP), chemical vapor deposition (CVD), physical vapor deposition (PVD), and electroplating deposition (EPD). The permeability of hydrogen in different Pd-based alloy membranes are presented and compared. Focus has been made, in this review, on Pd–Ag, Pd–Cu, Pd–Au, and Pd–Ru alloys. The effects of impurities (H2S, CO, O2, and CO2) on performance of different Pd-based alloy membranes are also investigated. Moreover, the subject of using Pd-membrane reactors for fuel reforming and H2 production is investigated in detail based on numerous experimental and numerical studies in the literature, considering different membrane reactor designs: axial-flow tubular, radial-flow tubular, axial-flow spherical, packed-bed, fluidized bed, and slurry bubble column. The performance of Pd-membranes in such reactors for hydrogen production is compared, and the effects of temperature, pressure, H2O/CH4 ratio, and residence time on reformer performance are also investigated. Finally, the use of computational methods, particularly, density functional theory (DFT), to complement well-established experimental methods for studying the diffusion of H and its isotopes in different metals is reviewed. The review concludes with some insights into future work to bring Pd-membrane reactors to the level required for hydrogen production at the commercial level.

Developing a bio‐inspired catalyst with the efficiency of homogeneous catalysts and recyclability similar to heterogeneous catalysts is quite desirable but challenging. Incorporation of metal nanoparticles (<10 nm) on abundant, low‐cost supports from agricultural waste can yield highly active and product‐selective pseudo‐homogeneous catalysts, with attributes such as ease of retrieval for next use, reusability, etc. In this work, the fabrication of an efficient and reusable ‘dip‐catalyst’ by anchoring platinum nanoparticles on white jute plant (Corchorus capsularis) stems (JPS) and its use for the hydrogenation of N‐heteroarenes, unfunctionalized olefins, and imines are described. The catalyst was characterized using XRD, SEM, EDS, TEM, HRTEM, FTIR, and XPS, and TEM shows spherical (average diameter 4–5 nm) non‐agglomerated metal nanoparticles. Catalyst was used for the chemoselective (>99 % selectivity) hydrogenation of quinoline with a quantitative (>99 %) conversion to 1,2,3,4‐tetrahydroquinoline (py‐THQ) under hydrogen at a pressure <30 bar. Also, functional group tolerance is indicated by the quantitative hydrogenation of 6‐chloroquinoline to 6‐chloro‐1,2,3,4‐tetrahydroquinoline, which is a longstanding challenge owing to C−Cl bond cleavage. In the hydrogenation of structurally‐challenging trisubstituted trans‐2‐methyl‐3‐phenyl‐2‐propen‐1‐ol olefins, 64 % conversion and >99 % selectivity was achieved. A series of imines with different chain lengths was also hydrogenated selectively in methanol with >99 % conversion. Density functional theory (DFT) calculations reveal the efficient adsorption of 6‐chloroquinoline on the surface of Pt nanoparticles on Pt@JPS strips in a tilted orientation placing the C−Cl bond away from the metal and allowing facile desorption of 6‐chloro‐1,2,3,4‐tetrahydroquinoline leading to higher chemoselectivity. The spent catalyst can be reused for 12 consecutive cycles without significant damage to the cellulosic surface.

Strict emission control regulations call for continuous advancement in existing combustion and carbon-capture technologies to mitigate the rise in pollutants and greenhouse gases from fossil fuel combustion. Concurrently, improvements in combustion systems would also yield lower fuel consumption and operational cost with greater efficiency. This review addresses these concerns and presents the overview of different combustion technologies and burner designs for cleaner power generation in gas turbines. Emission characteristics are discussed and compared for different combustion concepts, including lean premixed air combustion and oxy-combustion. Various gas turbine burner technologies, including dry low NO x , enhanced-vortex, perforated-plate, and micromixer burners, are discussed extensively, in terms of their operating principle, fuel flexibility, and potential for superior performance under oxy-combustion conditions. Enhanced-vortex and micromixer burners show remarkable flame stability and fuel flexibility and are thus recommended for implementation with hydrogen enrichment in future oxy-fuel gas turbines. The fuel-flexibility approaches for clean energy production, such as hydrogen combustion, hydrogen-enriched combustion, syngas combustion, ammonia combustion, and fuel blending, are explored as well. With the vast recent advances in the techniques of hydrogen production and storage, hydrogen-fueled gas turbines seem to be the perfect choice for clean energy production. The adiabatic flame temperature is identified as a key controlling parameter for the design of oxidizer-flexible combustors in clean gas turbines.

This review overviews combustion technologies for reduced emissions and better fuel economy in industrial gas turbine. Lean premixed combustion (LPM) technology is introduced as a low-temperature combustion technique to control NOx emissions. The Dry Low NOx (DLN) is one of the most promising LPM-based combustors for controlling NOx emissions. However, DLN combustors suffer from limited flame stability, especially under low load (near blowout) operating conditions, in addition to the difficulty of separating CO2 from the exhaust stream for reducing the gas-turbine carbon footprint. Trying to overcome such difficulties, the gas turbine manufacturers developed enhanced-design burners for higher turndown and lower NOx emissions, including the Dual Annular Counter Rotating Swirl (DACRS) and environmental-Vortex (EV) burners. The volume of the DACRS combustors is almost twice the conventional burners, which provide ample residence time for complete combustion. The mixing effectiveness is improved in EV-burners resulting in higher flame stability at low load or startup conditions. To widen the operability, control the emissions, and improve the turndown ratio of gas turbine combustors, the concept of flame stratification, i.e., heterogenization of the overall equivalence ratio, was introduced. This technique can widen the stability range of existing LPM flames for industrial applications. Integrating stratified combustion technique with oxy-fuel combustion technology is a way forward that may result in complete control of gas turbine emissions with higher operability turndown ratio. The recent developments and challenges towards the application of hydrogen gas turbine are introduced.

Premixed oxy-combustion flames of methane, syngas (CH 4 :CO:H 2 with the molar ratio of 2:1:1), and propane in CO 2 -diluted environment (for carbon capture) are examined in a swirl-stabilized combustor using large eddy simulations (LES) in three-dimensional (3-D) domain. The flame and emission characteristics are examined for the different fuels over a range of equivalence ratios (Φ: 0.34, 0.39, and 0.42), at 60% oxygen fraction (OF), and 2.5 m/s bulk inlet velocity under atmospheric conditions. The results indicate increments in several characteristic parameters that are of special importance for gas turbine combustion applications, including adiabatic flame temperature (T ad ), laminar flame speed (LFS), power density (PD), product formation rate (PFR), Damköhler number (Da), and CO emission, with the increase of Φ whatever the type of fuel. Alternatively, flame thickness (δ) decreases with the increase in Φ for the three fuels. Characteristic "V" shape with almost identical outer recirculation zone (ORZ) is also observed for the three fuels. Among the studied fuels, oxy-methane flames demonstrate highest flame thicknesses, least uniform temperature distribution (highest pattern factor) at combustor outlet, and lowest CO emission level. Oxy-syngas flames show more uniform temperature distribution (lowest pattern factor) at combustor outlet and highest CO emission as compared with the oxy-methane and oxy-propane flames. The oxy-propane flames have higher values of T ad , LFS, PD, PFR, Da, and thermal power (TP) along with lowest flame thickness compared with methane and syngas counterparts. Highlights• Increasing equivalence ratio improves the flame characteristics but increases CO emission.• Fuel type has insignificant effects on shape/size of the outer recirculation zone (ORZ).• Oxy-methane flames showed highest flame thicknesses and pattern factor and lowest CO.