Impacts of Combined Cooling, Heating and Power Systems, and Rainwater Harvesting on Water Demand, Carbon Dioxide, and NOx Emissions for Atlanta

Combined Heat and Power May Conflict with Decarbonization Goals-Air Emissions of Natural Gas Combined Cycle Power versus Combined Heat and Power Systems for Commercial Buildings

This study compares the environmental impacts of a centralized natural gas combined cycle (NGCC) and a distributed natural gas-fired combined heat and power (CHP) energy system in the United States. We develop an energy-balance model in which each energy system supplies the electric, heating, and cooling demands of 16 commercial building types in 16 climate zones of the United States. We assume a best-case scenario where all the CHP's heat and power are allocated toward building demands to ensure robust results. We quantify the greenhouse gas (GHG) emissions, conventional air pollutants (CAPs), and natural gas (NG) consumption. In most cases, the decentralized CHP system increases GHG emissions, decreases CAP emissions, and decreases NG consumption relative to the centralized NGCC system. Only fuel-cell CHPs were able to simultaneously reduce GHG, CAP, and NG consumption relative to the NGCC-based system. The results suggest that despite their energy efficiency benefits, standard distributed CHP-based systems typically do not have enough benefits compared to an NGCC-based system to justify a reorganization of existing infrastructure systems. Because fuel-cell CHPs can also use hydrogen as a fuel source, they are compatible with decarbonized energy systems and may aid in the transition toward a cleaner energy economy.

Highly Active CO2 Fixation into Cyclic Carbonates Catalyzed by Tetranuclear Aluminum Benzodiimidazole-Diylidene Adducts

A set of tetranuclear alkyl aluminum adducts 1 and 2 supported by benzodiimidazole-diylidene ligands L1, N,N’-(1,5-diisopropylbenzodiimidazole-2,6-diylidene)bis(propan-2-amine), and L2, N,N’-(1,5-dicyclohexyl-benzodiimidazole-2,6-diylidene)dicyclohexanamine were synthetized in exceptional yields and characterized by spectroscopic methods. These compounds were studied as catalysts for cyclic carbonate formation (3a–o) from their corresponding terminal epoxides (2a–o) and carbon dioxide utilizing tetrabutylammonium iodide as a nucleophile in the absence of a solvent. The experiments were carried out at 70 °C and 1 bar CO2 pressure for 24 h and adduct 1 was the most efficient catalyst for the synthesis of a large variety of monosubstituted cyclic carbonates with excellent conversions and yields.

Alkali-Resistant NOx Reduction over SCR Catalysts via Boosting NH3 Adsorption Rates by In Situ Constructing the Sacrificed Sites

Currently, improving the alkali resistance of vanadium-based catalysts still remains as an intractable issue for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). It is generally believed that the decrease in adsorbed NH_x species deriving from the declined acidic sites is the chief culprit for the deactivation of alkali-poisoned catalysts. Herein, alkali-resistant NO_x reduction over SCR catalysts via boosting NH₃ adsorption rates was originally demonstrated by in situ constructing the sacrificed sites. It is interesting that the adsorbed NH_x species largely decrease while the NH₃ adsorption rate is well kept over the V₂O₅/CeO₂ catalyst by in situ constructing the sacrificed sites. The SCR activity could be maintained after alkali poisoning because in situ constructed SO₄^2- groups would prefer to be combined with K⁺ so that the specific V═O species can endow K-poisoned V₂O₅/CeO₂ with high adsorption rate of NH₃ and high reactivity of NH_x species. This work provides a new viewpoint that NH₃ adsorption rate plays more decisive roles in the performance of alkali-poisoned catalysts than the amount of NH₃ adsorption and enlightens an alternative strategy to improve the alkali-resistance of catalysts, which is significant to both the academic and industrial fields.

SO2-Tolerant Selective Catalytic Reduction of NO x over Meso-TiO2@Fe2O3@Al2O3 Metal-Based Monolith Catalysts

It is an intractable issue to improve the low-temperature SO₂-tolerant selective catalytic reduction (SCR) of NO _x with NH₃ because deposited sulfates are difficult to decompose below 300 °C. Herein, we established a low-temperature self-prevention mechanism of mesoporous-TiO₂@Fe₂O₃ core-shell composites against sulfate deposition using experiments and density functional theory. The mesoporous TiO₂-shell effectively restrained the deposition of FeSO₄ and NH₄HSO₄ because of weak SO₂ adsorption and promoted NH₄HSO₄ decomposition on the mesoporous-TiO₂. The electron transfer at the Fe₂O₃ (core)-TiO₂ (shell) interface accelerated the redox cycle, launching the "Fast SCR" reaction, which broadened the low-temperature window. Engineered from the nano- to macro-scale, we achieved one-pot self-installation of mesoporous-TiO₂@Fe₂O₃ composites on the self-tailored AlOOH@Al-mesh monoliths. After the thermal treatment, the mesoporous-TiO₂@Fe₂O₃@Al₂O₃ monolith catalyst delivered a broad window of 220-420 °C with NO conversion above 90% and had superior SO₂ tolerance at 260 °C. The effective heat removal of Al-mesh monolithcatalysts restrained NH₃ oxidation to NO and N₂O while suppressing the decomposition of NH₄NO₃ to N₂O, and this led to much better high-temperature activity and N₂ selectivity. This work supplies a new point for the development of low-temperature SO₂-tolerant monolithic SCR catalysts with high N₂ selectivity, which is of great significance for both academic interests and practical applications.

Fe2O3-CeO2@Al2O3 Nanoarrays on Al-Mesh as SO2-Tolerant Monolith Catalysts for NO x Reduction by NH3

Currently, selective catalytic reduction of NO _x with NH₃ in the presence of SO₂ is still challenging at low temperatures (<300 °C). In this study, enhanced NO _x reduction was achieved over a SO₂-tolerant Fe-based monolith catalyst, which was originally developed through in situ construction of Al₂O₃ nanoarrays (na-Al₂O₃) on the monolithic Al-mesh by a steam oxidation method followed by anchoring Fe₂O₃ and CeO₂ onto the na-Al₂O₃@Al-mesh composite by an impregnation method. The optimum catalyst delivered more than 90% NO conversion and N₂ selectivity above 98% within 250-430 °C as well as excellent SO₂ tolerance at 270 °C. The strong interaction between Fe₂O₃ and CeO₂ enabled favorable electron transfers from Fe₂O₃ to CeO₂ while generating more oxygen vacancies and active oxygen species, consequently accelerating the redox cycle. The improved reactivity of NH₄⁺ with nitrates following the Langmuir-Hinshelwood mechanism and active NH₂ species that directly reacted with gaseous NO following the Eley-Rideal mechanism enhanced the NO _x reduction efficiency at low temperatures. The preferential sulfation of CeO₂ alleviated the sulfation of Fe₂O₃ while maintaining the high reactivities of NH₄⁺ and NH₂ species. Especially, the SCR reaction following the Eley-Rideal mechanism largely improved the SO₂ tolerance because NO does not need to compete with sulfates to adsorb on the catalyst surface as nitrates or nitrites. This work paves a way for the development of high-performance SO₂-tolerant SCR monolith catalysts.

Improved NO x Reduction in the Presence of SO2 by Using Fe2O3-Promoted Halloysite-Supported CeO2-WO3 Catalysts

Currently, selective catalytic reduction (SCR) of NO _x with NH₃ in the presence of SO₂ by using vanadium-free catalysts is still an important issue for the removal of NO _x for stationary sources. Developing high-performance catalysts for NO _x reduction in the presence of SO₂ is a significant challenge. In this work, a series of Fe₂O₃-promoted halloysite-supported CeO₂-WO₃ catalysts were synthesized by a molten salt treatment followed by the impregnation method and demonstrated improved NO _x reduction in the presence of SO₂. The obtained catalyst exhibits superior catalytic activity, high N₂ selectivity over a wide temperature range from 270 to 420 °C, and excellent sulfur-poisoning resistance. It has been demonstrated that the Fe₂O₃-promoted halloysite-supported CeO₂-WO₃ catalyst increased the ratio of Ce³⁺ and the amount of surface oxygen vacancies and enhanced the interaction between active components. Moreover, the SCR reaction mechanism of the obtained catalyst was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy. It can be inferred that the number of Brønsted acid sites is significantly increased, and more active species could be produced by Fe₂O₃ promotion. Furthermore, in the presence of SO₂, the Fe₂O₃-promoted halloysite-supported CeO₂-WO₃ catalyst can effectively prevent the irreversible bonding of SO₂ with the active components, making the catalyst exhibit desirable sulfur resistance. The work paves the way for the development of high-performance SCR catalysts with improved NO _x reduction in the presence of SO₂.