Gases

This review examines the emerging concepts of hydrogen production and storage directly within hydrocarbon reservoirs (in situ), evaluating their technical feasibility, infrastructure requirements, challenges, and potential role in net-zero strategies. The in situ hydrogen production involves injecting substances, like water or gases, into the reservoir where they react with the natural materials underground. Heat and catalysts can also help speed up chemical reactions. Techniques such as methane reforming, steam gasification, and aquathermolysis show promise for producing hydrogen efficiently while keeping carbon emissions low. There are several benefits when producing and storing hydrogen underground, including lower costs, less need for surface equipment, and reduced gas emissions. However, there are still certain challenges to this process, such as finding the optimal reaction conditions and keeping the reservoir stable over time. This review outlines key technological breakthroughs, real-world applications, and future research directions for in situ hydrogen generation and storage initiatives to help meet net-zero emission goals by 2050.

This study examines the determinants of U.S. CO₂ emissions and provides evidence to inform more effective carbon-reduction policies. Using Autoregressive Distributed Lag (ARDL) and Nonlinear ARDL (NARDL) models, the analysis covers January 1997 to February 2022 across four end-use sectors: Residential, Commercial, Industrial, and Transportation. The models capture both long-run equilibria and short-run adjustments between emissions and key drivers, including industrial production, interest rates, climate policy uncertainty (CPU), and energy prices. Results indicate a long-run asymmetric relationship in which economic growth and interest rates differentially affect total emissions, while CPU exerts a significant negative influence only in the transportation sector. Methodologically, the combined ARDL–NARDL approach offers robust evidence of nonlinear and asymmetric effects of macroeconomic and policy variables on emissions. These findings underscore the need to integrate economic and financial conditions into climate policy design and suggest that sector-specific measures—particularly targeting transportation—may substantially improve the effectiveness of carbon-mitigation strategies.

Anaerobic digestion (AD) of ensiled orange peel waste (OPW) offers a promising pathway for the valorisation of citrus-processing residues and the generation of renewable energy. This study evaluated the impact of two carbon-based materials, biochar and granular activated carbon (GAC), on methane yield and process stability using Biochemical Methane Potential (BMP) tests. The experimental setup consisted of two consecutive cycles, the second of which was designed to examine microbial acclimation by reusing both the digestate (as the inoculum) and the previously added carbon materials. Ensiled OPW exhibited a methane yield of 578 ± 59 mL_CH4/g_VS during the initial cycle, confirming its high biodegradability. The addition of biochar and GAC resulted in comparable yields (approximately 520–560 mL_CH4/g_VS) and did not enhance the ultimate methane potential; however, both additives proved fully compatible with the process. In the subsequent cycle, a marked increase in methane production was observed, with OPW reaching approximately 730 mL_CH4/g_VS, primarily attributed to improved microbial adaptation. Kinetic analysis revealed moderate enhancements in degradation rates, which were more pronounced when higher biochar dosages were used. Overall, ensiled OPW emerges as a highly suitable substrate for AD. At the same time, biochar and GAC did not adversely affect the AD process under the tested conditions; however, their potential benefits have yet to be fully demonstrated and warrant further investigation, particularly under continuous reactor operating conditions.