Measurements of Particulate (PM2.5), BC and Trace Gases Over the Northwestern Himalayan Region of India

Ambient trace gases (NH₃, NO, NO₂ and SO₂) and black carbon (BC) were measured along with particulate matter (PM_2.5) over the northwestern Himalayan region (Palampur, Kullu, Shimla, Solan and Nahan) of Himachal Pradesh (HP), India in a campaign mode during 12–22 March 2013 to evaluate the ambient air quality of the region. The average mixing ratio of ambient NH₃, NO, NO₂ and SO₂ were recorded as 7.1 ± 2.6, 3.1 ± 1.3, 3.9 ± 1.4 and 1.7 ± 0.7 ppb respectively over the northwestern Himalayan region. The average concentration of BC was estimated as 2.2 ± 0.5 µg m^?3 over the region whereas average concentration of PM_2.5 mass was estimated as 41.8 ± 7.9 µg m^?3. The spatial variation of ambient trace gases (NH₃, NO, NO₂ and SO₂), BC and PM_2.5 over the northwestern Himalayan region, India reveals that the region is mainly influenced by local activities, i.e., tourism activities, agricultural activities, biomass burning and vehicular emission. A significant positive linear correlation of NH₃ and NH₄ ⁺ with SO₄ ^2?, NO₃ ^? and Cl^? (NH₄ ⁺ vs. SO₄ ^2? , r ² = 0.652; NH₄ ⁺ vs. NO₃ ^?, r ² = 0.701; and NH₄ ⁺ vs. Cl^?, r ² = 0.627) of the PM_2.5 indicates the possible formation of (NH₄)₂SO₄, NH₄NO₃ and NH₄Cl aerosols over the region.     

Economic and environmental evaluation of coal-and-biomass-to-liquids-and-electricity plants equipped with carbon capture and storage

Among various clean energy technologies, one innovative option for reducing the emission of greenhouse gases (GHGs) and criteria pollutants involves pairing carbon capture and storage (CCS) with the production of synthetic fuels and electricity from a combination of coal and sustainably sourced biomass. With a relatively pure CO₂ stream as an inherent byproduct of the process, most of the resulting GHG emissions can be eliminated by simply compressing the CO₂ for pipeline transport. Subsequent storage of the CO₂ output in underground reservoirs can result in very low—perhaps even near-zero—net GHG emissions, depending on the fraction of biomass as input and its CO₂ signature. To examine the potential market penetration and environmental impact of coal-and-biomass-to-liquids-and-electricity (CBtLE), a system-wide sensitivity analysis was performed using the MARKet ALlocation energy model. CBtLE was found to be most competitive in scenarios with a combination of high oil prices, low CCS costs, and, unexpectedly, non-stringent carbon policies. In the scheme considered here (30 % biomass input on an energy basis and 85 % carbon capture), CBtLE fails to achieve significant market share in deep decarbonization scenarios, regardless of oil prices and CCS costs. Such facilities would likely require higher fractions of biomass feedstock and captured CO₂ to successfully compete in a carbon-constrained energy system.     

Combustion of agro-waste with coal in a fluidized bed

In this study, a review of the studies done on the co-combustion of some agro-waste in a bubbling fluidized bed combustor (BFBC) having an inside diameter of 102 mm and a height of 900 mm is given. The agro-waste used to investigate the co-combustion characteristics were peach and apricot stones produced as a waste from the fruit juice industry, and olive cake produced as a waste from the olive oil industry. These are typical wastes for a Mediterranean country. A lignite coal was used for co-combustion. On-line concentrations of O₂, CO, CO₂, SO₂, NO _x and total hydrocarbons (C _m H _n ) were measured in the flue gas during combustion experiments. Variations of emissions of various pollutants were studied by changing the operating parameters (excess air ratio, fluidization velocity and fuel feed rate). Temperature distribution along the bed was measured with thermocouples. Emissions were also monitored from the exhaust. Various combinations of coal and biomass mixtures were tested. During the combustion tests, it was observed that the volatile matter from the biomass quickly volatilizes and mostly burns in the freeboard. The temperature profiles along the bed and the freeboard also confirmed this phenomenon. It was found that as the volatile matter of the biomass increases, combustion takes place more in the freeboard region. Better combustion conditions occur at higher excess air ratios. The results showed that co-combustion with these three proposed biomasses lowers the SO₂ and NO _x emissions considerably. CO and hydrocarbon emissions are lower at the higher excess air ratios.     

Characterization of atmospheric corrosion products of zinc exposed to SO<Subscript>2</Subscript> and NO<Subscript>2</Subscript> using XPS and GIXD

A complete characterization of corrosion products formed on zinc plates after exposure in a climatic chamber was conducted in this study. The dry deposition of NO₂, SO₂, and SO₂ + NO₂, at 25 °C and 35 °C, and relative humidity (RH) of 90% was simulated. Pollutant concentrations evaluated were selected to represent highly polluted industrial atmospheric levels. Analysis techniques included X-ray Photoelectron Spectroscopy (XPS) and Grazing Incidence X-ray Diffraction (GIXD). For tests conducted at 25 °C, the relative amount of sulfate was determined to be higher in the SO₂ + NO₂ atmosphere than in the SO₂ atmosphere, and was associated with greater corrosivity in the former atmosphere. NO₂ had an indirect role as a catalyst for SO₂ reduction to sulfate, as evidenced by the greater proportion of sulfate ions detected and the lack of nitrogen compounds in corrosion products. At 35 °C, effect of NO₂ was reduced, and was complicated by a greater tendency for drying so that it was more difficult to maintain the humidity layer. Therefore, no accelerating effect of exposure temperature was observed.     

High performance magnetically recoverable g-C3N4/Fe3O4/Ag/Ag2SO3 plasmonic photocatalyst for enhanced photocatalytic degradation of water pollutants

The g-C₃N₄/Fe₃O₄/Ag/Ag₂SO₃ nanocomposites have been successfully fabricated by facile refluxing method. The as-obtained products were characterized by XRD, EDX, SEM, TEM, UV–vis DRS, FT–IR, TGA, PL, and VSM techniques. The results suggest that the Ag/Ag₂SO₃ nanoparticles have anchored on the surface of g-C₃N₄/Fe₃O₄ nanocomposite, showing strong absorption in the visible region. The evaluation of photocatalytic activity indicates that for the g-C₃N₄/Fe₃O₄/Ag/Ag₂SO₃ (40%) nanocomposite, the degradation rate constant was 188 × 10^?4 min^?1 for rhodamine B, exceeding those of the g-C₃N₄ (16.0 × 10^?4 min^?1) and g-C₃N₄/Fe₃O₄ (20.2 × 10^?4 min^?1) by factors of 11.7 and 9.3, respectively. The results showed that the nanocomposite prepared by refluxing for 120 min has the superior photocatalytic activity and its activity decreased with rising the calcination temperature. The trapping experiments confirmed that superoxide ion radical was the main active species in the photocatalytic degradation process. Also, it was demonstrated that the magnetic photocatalyst has considerable activity in degradation of one more dye pollutant. Finally, the reusability of the photocatalyst was evaluated by five consecutive catalytic runs. This work may open up new insights into the utilization of magnetically separable nanocomposites and provide new opportunities for facile fabrication of g-C₃N₄-based plasmonic photocatalysts.     

Fabrication and characterization of nanostructured (Sn–Ti)O<Subscript>2</Subscript> pellets and films for liquefied petroleum gas sensing

Present paper reports the synthesis of nanostructured (Sn–Ti)O₂ via physicochemical method, its characterization and performance as liquefied petroleum gas (LPG) sensor. The synthesized material was characterized using XRD that confirmed the formation of (Sn–Ti)O₂ nanocomposite. Minimum crystallite size was found as 7 nm. The material was also investigated through SEM, DSC, FTIR, PL and UV–Vis spectrophotometer. Further, the pellet, thick and thin films were fabricated for the sensing analysis. Pellets (9 mm diameter, 4 mm thickness) of (Sn–Ti)O₂ nanocomposite were made by hydraulic pressing machine by applying uniaxial pressure of 616 MPa, thick films (thickness ~2 µm) were made by screen printing technique and thin films were prepared using a Photo resist spinner unit. Further at room temperature, the pellet and films were exposed to LPG in a gas chamber under controlled conditions at room temperature and variations in resistance with the concentrations of LPG were observed. The maximum value of sensitivity of solid state pellet, thick and thin films based sensors were found 7, 9 and 39 for 5 vol% of LPG, respectively. Sensing characteristics were found to be reproducible, after 6 months of their fabrication, indicating the stability of the sensors.     

Cement and carbon emissions

Because of its low cost, its ease of use and relative robustness to misuse, its versatility, and its local availability, concrete is by far the most widely used building material in the world today. Intrinsically, concrete has a very low energy and carbon footprint compared to most other materials. However, the volume of Portland cement required for concrete construction makes the cement industry a large emitter of CO₂. The International Energy Agency recently proposed a global CO₂ reduction plan. This plan has three main elements: long term CO₂ targets, a sectorial approach based on the lowest cost to society, and technology roadmaps that demonstrate the means to achieve the CO₂ reductions. For the cement industry, this plan calls for a reduction in CO₂ emissions from 2 Gt in 2007 to 1.55 Gt in 2050, while over the same period cement production is projected to increase by about 50 %. The authors of the cement industry roadmap point out that the extrapolation of existing technologies (fuel efficiency, alternative fuels and biomass, and clinker substitution) will only take us half the way towards these goals. According to the roadmap, the industry will have to rely on costly and unproven carbon capture and storage technologies for the other half of the required reduction. This will result in significant additional costs for society. Most of the CO₂ footprint of cement is due to the decarbonation of limestone during the clinkering process. Designing new clinkers that require less limestone is one means to significantly reduce the CO₂ footprint of cement and concrete. A new class of clinkers described in this paper can reduce CO₂ emissions by 20 to 30 % when compared to the manufacture of traditional PC Clinker.     

An assessment of hydrothermal treatment of dairy waste as a tool for a sustainable phosphorus supply chain in comparison with commercial phosphatic fertilizers

Hydrothermal treatment has been proven efficient in immobilizing phosphorus and other macronutrients from animal waste; however, there are still gaps in understanding the best end-use applications for nutrient-dense biochars. In this research, aqueous phase phosphorus availability (P _aq) of biochars produced at various temperatures and residence times was determined in pH 5.5 citric acid for 8 weeks. Further, P _aq of commercially available composted manure and fertilizers was also determined for comparison. P _aq was found to plateau after 4 weeks in aqueous phase. Hydrothermal treatment temperature and residence time were found to improve nutrient immobilization efficiency, while conversely lowering P _aq. Comparing to commercially available fertilizers, biochars produced from hydrothermal treatment are low in P _aq, despite high P₂O₅% found in the solids. A preliminary process study evaluating energy consumption and CO₂ emissions associated with recycled P₂O₅ recovered from the process operating at 200 °C was conducted, indicating CO₂ emissions with respect to soluble phosphorus are significantly higher in comparison with commercial phosphatic fertilizers. Further recommendations regarding life cycle analysis of the phosphorus supply chain are also discussed.     

Particle size effects in Rh/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts as viewed from a structural,functional, and reactive perspective: the case of the reactive adsorption of NO

The structural-dynamic behaviour of γ-Al₂O₃ supported Rh nanoparticles under He, H₂/He, and NO/He has been investigated using a newly developed methodology that permits dispersive EXAFS (EDE), diffuse reflectance infra red spectroscopy (DRIFTS), and mass spectrometry (MS) to be applied simultaneously to the study of gas-solid interactions. This reveals a considerably variability in nanoparticle habit (for 11 Å diameter nanoparticles as a function of temperature), and between 8 Å and 11 Å particles in their response to NO. The selectivity (N₂/(N₂ + N₂O)) of the reactive interaction between NO and the supported Rh shows essentially no particle size dependence above 473 K: it is apparent, however, that considerable differences in some aspects of the structural behaviour of the 8 Å and 11 Å Rh particles do nonetheless, exist. At 373 < T < 473 K a clear divergence in structural, functional, and reactive response of the different sized supported Rh nanoparticles toward NO is observed. These observations are discussed in terms of the ability of different sized Rh particles to change structure in response to the reactive environment, the subsequent effect this has on the nitrosyl functionality that different phases may support, and the reactive pathways for NO conversion that may therefore arise.     

A scheme for solving strongly coupled chemical reaction equations appearing in the removal of SO2 and NOx from flue gases

The removal of NO_x from mixtures of NO-NO₂-N₂ and NO-NO₂-O₂-H₂O is discussed theoretically in this study, and the removal of ₂SO and xNO is further discussed when a gas system of NO_x-N₂-O₂-H₂O contains CO₂ and SO₂. The involved chemical reaction rate equations in the process of SO₂/NO_x removal are solved numerically using Treanor's method, in which a scheme separating chemical reactions into fast and slow groups has been proposed for improving the numerical stability. Numerical results show that the contribution of ion reactions to xNO removal is negligible, and that high temperature is not beneficial for the NO oxidation. However, high concentration of O₂ is conducive to the NO oxidation. Addition of water facilitates the NO_x removal, and increasing water vapor concentration enhances the NO_x removal efficiency; inclusion of CO₂ and SO₂ into the system favors the NO removal.     

Semiconducting behaviour of RuGa2

RuGa₂ with TiSi₂-type structure was prepared by inductively heating ruthenium and gallium in a water-cooled copper boat under argon atmosphere. The electrical conductivity of a polycrystalline sample of nearly rectangular shape (7 × 5 × 4 mm³) was measured in the temperature range from 20 °C to 400 °C by the four-point technique. RuGa₂ is a semiconductor with an electrical resistivity of 0.2 ohm · cm at room temperature and a bandgap of ～ 0.42 eV. Semiconducting properties have been qualitatively demonstrated for RuAl₂ (TiSi₂-type structure) and for Os₂Si₃ (Ru₂Si₃-type structure, defect TiSi₂-structure).     

Impedance spectroscopy studies of bulk electrical conduction in A-site acceptor (K)-doped BaTiO3

BaTiO₃ ceramics with different acceptor concentrations of potassium at A-site Ba_1?x K _x TiO_3?x/2 (BKT) were prepared by solid-state processes. The solution limit of potassium in BKT is determined to be 1 mol%. Furthermore, electrical conduction behaviours were investigated in the temperature range of 300–800 °C by analysing impedance spectra and were found extremely depending on processing and measurement conditions. When annealed at 800 °C and measured in an atmosphere of dry N₂, BKT is a mixed oxide ion/electron conductor and its ionic transference number decreases with increasing temperature. But when annealed at 800 °C and measured in an atmosphere of dry air and O₂, BKT is a p-type semiconductor with a transition from a trapped holes’ conduction to activated holes’ conduction as temperature increases. On exposure of BKT to an atmosphere of wet N₂, BKT is a proton conductor in the temperature of 300–550 °C; however, it reverts to a p-type semiconductor above 550 °C as water is lost from the sample.     

Simultaneous reduction of NO–smoke–CO<Subscript>2</Subscript> emission in a biodiesel engine using low-carbon biofuel and exhaust after-treatment system

The present work focuses on the simultaneous reduction of NO–smoke–CO₂ emission in a Karanja oil methyl ester (KOME)-fueled single-cylinder compression ignition engine by using low-carbon biofuel with exhaust after-treatment system. Replacement of KOME for diesel reduced smoke emission by 3% but resulted in increase of NO emission and CO₂ emission by 13 and 35% at 100% load condition. In order to reduce CO₂ emission, tests were conducted with a blend of KOME and orange seed oil (OSO), a low-carbon fuel on equal volume basis (50–50). At the same operating conditions, compared to KOME, 27% reduction in CO₂ emission and 5% reduction in smoke emission were observed. However, a slight increase in NO emission was observed. To achieve simultaneous reduction of NO–smoke–CO₂ emissions, three catalysts, namely monoethanolamine, zeolite and activated carbon, were selected for exhaust after-treatment system and tested with optimum KOME–OSO blend. KOME–OSO + zeolite showed a great potential in simultaneous reduction of NO–smoke–CO₂ emissions. NO, smoke and CO₂ emissions were simultaneously reduced by about 15% for each emission compared to diesel at 100% load condition. The effect of exhaust after-treatment system with KOME–OSO blend on combustion, performance and other emission parameters is discussed in detail in this study. Fourier transform infrared spectrometry analysis and testing were done to identify the absorbance characteristics of zeolite material.     

Measurement of Ambient NH<Subscript>3</Subscript>, NO and NO<Subscript>2</Subscript> at an Urban Area of Kolkata,India

Mixing ratios of ambient NH₃, NO and NO₂ were measured in campaign mode at Kolkata a megacity of Indo-Gangetic plain of India to study the diurnal variation and mixing ratios of NH₃, NO and NO₂ during 24–27 February 2012. The present study has been carried out on campaign based measurement of mixing ratios of NH₃, NO and NO₂ for short period of time at Kolkata represent the indicative values over the region. The average mixing ratios of ambient NH₃, NO and NO₂ were recorded as 43.4 ± 7.0 ppb, 46.0 ± 8.7 ppb and 31.9 ± 5.5 ppb at Kolkata. In the present case, significant diurnal variation of NH₃, NO and NO₂ were recorded at Kolkata during study. Mixing ratio of ambient NH₃ reaches its maxima (78.9 ppb) at night and minimum during daytime. Result reveals that the ambient NH₃ mixing ratio is positively correlated with ambient NO (r ² = 0.395) and NO₂ (r ² = 0.404) mixing ratio and significant negatively correlated with ambient temperature (r ² = –0.669). Surface wind direction and wind speed analysis indicates that the local acitivities (livestock, drainage, agriculture, vehicles etc.,) may be the possible sources of ambient NH₃ at the observational site of Kolkata.     

Phase evolution and reaction mechanism during reduction–nitridation process of titanium dioxide with ammonia

Titanium nitride powders were synthesized from titanium dioxide at 1173–1373 K in ammonia atmosphere. The reduction–nitridation products with various fractions obtained at various temperatures were analyzed by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The reaction sequence from TiO₂ to TiN in ammonia atmosphere was changed by increasing the reaction temperature. The reaction sequence at 1173 K was found as TiO₂ → TiN_1?xO_x → TiN. When the reaction temperature was above 1273 K, the reaction sequence changed to as follows: TiO₂ → Ti₉O₁₇ → TiN_1?xO_x → TiN. Ti₃O₅ was not found as an intermediate phase on account of its instability in NH₃ atmosphere. The morphology of the synthesized TiN is closely related to that of the raw materials.     

Thermal conductivity and strength of foamed gypsum formulated using aluminum sulfate and sodium bicarbonate as gas-producing additives

The present work aimed to explore the potential of using Al₂(SO₄)₃ and NaHCO₃ as gas-producing additives for the formation of foamed gypsum. Three systems of additives, namely Al₂(SO₄)₃ + CaCO₃, Al₂(SO₄)₃ + citric acid, and NaHCO₃, were investigated for their foam-forming ability in order to lower the thermal conductivity while preserving the compressive strength of the foamed gypsum. Emphasis was given to the setting time such that it would lie within 20–25 min, for the formulation to be practically useful. The results showed that, within the desired setting time, NaHCO₃ provided the lowest thermal conductivity (~0.22 W/mK) and the highest efficiency (i.e., the highest rate of the thermal conductivity reduction for each percent of additives) among the three systems studied. It was also the system that best preserved the compressive strength for every unit reduction in the thermal conductivity. However, the corresponding compressive strength of 0.72 MPa was still very low, about three times lower than that of the other systems. The Al₂(SO₄)₃ + CaCO₃ system yielded a lower thermal conductivity (~0.24 W/mK) than the Al₂(SO₄)₃ + citric system (~0.31 W/mK), although their corresponding compressive strengths (~2.4 MPa) were quite similar. Therefore, given the desired setting time, the Al₂(SO₄)₃ + CaCO₃ system produced the best combination of thermal conductivity and compressive strength.     

Sulfur dioxide initiates global climate change in four ways

Global climate change, prior to the 20th century, appears to have been initiated primarily by major changes in volcanic activity. Sulfur dioxide (SO²) is the most voluminous chemically active gas emitted by volcanoes and is readily oxidized to sulfuric acid normally within weeks. But trace amounts of SO₂ exert significant influence on climate. All major historic volcanic eruptions have formed sulfuric acid aerosols in the lower stratosphere that cooled the earth's surface ~ 0.5 °C for typically three years. While such events are currently happening once every 80 years, there are times in geologic history when they occurred every few to a dozen years. These were times when the earth was cooled incrementally into major ice ages. There have also been two dozen times during the past 46,000 years when major volcanic eruptions occurred every year or two or even several times per year for decades. Each of these times was contemporaneous with very rapid global warming. Large volumes of SO₂ erupted frequently appear to overdrive the oxidizing capacity of the atmosphere resulting in very rapid warming. Such warming and associated acid rain becomes extreme when millions of cubic kilometers of basalt are erupted in much less than one million years. These are the times of the greatest mass extinctions. When major volcanic eruptions do not occur for decades to hundreds of years, the atmosphere can oxidize all pollutants, leading to a very thin atmosphere, global cooling and decadal drought. Prior to the 20th century, increases in atmospheric carbon dioxide (CO₂) followed increases in temperature initiated by changes in SO₂.By 1962, man burning fossil fuels was adding SO₂ to the atmosphere at a rate equivalent to one “large” volcanic eruption each 1.7 years. Global temperatures increased slowly from 1890 to 1950 as anthropogenic sulfur increased slowly. Global temperatures increased more rapidly after 1950 as the rate of anthropogenic sulfur emissions increased. By 1980 anthropogenic sulfur emissions peaked and began to decrease because of major efforts especially in Japan, Europe, and the United States to reduce acid rain. Atmospheric concentrations of methane began decreasing in 1990 and have remained nearly constant since 2000, demonstrating an increase in oxidizing capacity. Global temperatures became roughly constant around 2000 and even decreased beginning in late 2007. Meanwhile atmospheric concentrations of carbon dioxide have continued to increase at the same rate that they have increased since 1970. Thus SO₂ is playing a far more active role in initiating and controlling global warming than recognized by the Intergovernmental Panel on Climate Change. Massive reduction of SO₂ should be a top priority in order to reduce both global warming and acid rain. But man is also adding two to three orders of magnitude more CO₂ per year to the climate than one “large” volcanic eruption added in the past. Thus CO₂, a greenhouse gas, is contributing to global warming and should be reduced. We have already significantly reduced SO₂ emissions in order to reduce acid rain. We know how to do it both technically and politically.In the past, sudden climate change was typically triggered by sudden increases in volcanic activity. Slow increases in greenhouse gases, therefore, do not appear as likely as currently thought to trigger tipping points where the climate suddenly changes. However we do need to start planning an appropriate human response to future major increases in volcanic activity.     

The influence of annealing atmosphere on the phase formation of Cu–Sn–S ternary compound by SILAR method

The influence of annealing atmosphere on the phase formation of Cu–Sn–S ternary compound by SILAR method was studied. Structural, optical and electrical properties of the compound were studied for the samples annealed at 420 °C for 1 h in different atmosphere. X-ray diffraction and Raman spectra showed that Cu₂SnS₃ cubic phase was obtained in an atmosphere of nitrogen and sulfur vapor mixture, while Cu₄SnS₄ orthorhombic phase was obtained in H₂S atmosphere. An optical band-gap of 0.98 eV was obtained for Cu₂SnS₃ and 0.93 eV for Cu₄SnS₄ phase. The activation energies are about 0.1 eV for Cu₂SnS₃ phase and 0.06 eV for the Cu₄SnS₄ phase in high temperature region, but those are about 0.007 and 0.009 eV for them in low temperature region respectively.     

Synthesis and characterisation of a porous Al scaffold sintered from NaAlH<Subscript>4</Subscript>

A simple and cost-effective method for the synthesis of a porous Al scaffold has been optimised using only NaAlH₄ and TiCl₃. The starting materials were compacted into a pellet and sintered under dynamic vacuum to remove the Na and H₂. The sintering conditions, such as vacuum level, temperature, and time, were the key factors that influenced both the extraction of Na and H₂ from the pellet and the overall porosity. Quantitative phase analysis by X-ray diffraction revealed that after the sintering process, the as-prepared porous Al scaffold consisted primarily of Al. Morphological observations conducted by scanning electron microscopy showed that the scaffold exhibited an open network of pores with a small number of mesopores and no formation of micropores. The specific surface area of the scaffold was determined to be 7.9 ± 0.1 and 6.0 ± 0.5 m²/g by the Brunauer–Emmet–Teller method and from small-angle X-ray scattering measurements, respectively. The total porosity of the Al scaffold was 44.6%.     

Photocatalytic CO<Subscript>2</Subscript> conversion over Au/TiO<Subscript>2</Subscript> nanostructures for dynamic production of clean fuels in a monolith photoreactor

Global economic development intensifies the consumption of fossil fuels which results in increase of carbon dioxide (CO₂) concentration in the atmosphere. The technologies for carbon capture and utilization to produce cleaner fuels are of great significance. However, phototechnology provides one perspective for economical CO₂ conversion to cleaner fuels. In this study, CO₂ conversion with H₂ to selective fuels over Au/TiO₂ nanostructures using environment friendly continuous monolith photoreactor has been investigated. Crystalline nanoparticles of anatase TiO₂ were obtained in the Au-doped TiO₂ samples. The Au deposited over TiO₂ in metal state produced plasmonic resonance. CO₂ was efficiently converted to CO as the main product over Au/TiO₂ with a maximum yield rate of 4144 µmol g-catal.^?1 h^?1, 345 fold-higher than using un-doped TiO₂ catalyst. The significantly enhanced photoactivity of Au/TiO₂ catalyst was due to hindered charges recombination rate and Au metallic-interband transition. The photon energy in the UV range was high enough to excite the d-band electronic transition in the Au to produce CO, CH₄, and C₂H₆. The quantum efficiency over Au/TiO₂ catalyst for CO was considerably improved in the continuous monolith photoreactor. At higher space velocity, the yield rates of CO gradually reduced, but the initial rates of hydrocarbon yields increased. The stability of the recycled Au/TiO₂ catalyst was sustained in cyclic runs. Thus, Au-doped TiO₂ supported over monolith channels is promising for enhanced CO₂ photoreduction to high energy products. This provides pathway that phototechnology to be explored further for cleaner and economical fuels production.