Catalytic Reforming and Hydrogen Production: From the Past to the Future, 2nd Edition

The continuously increasing global energy demand, combined with the urgent need to mitigate climate change and reduce greenhouse gas emissions, has intensified research efforts for developing sustainable energy technologies [1,2]. Among the various alternative energy carriers, hydrogen (H₂) has emerged as one of the most promising options due to its high energy density, clean combustion, and potential integration with renewable energy systems [3,4]. Consequently, the development of efficient catalytic processes for producing H₂ has recently attracted considerable attention.

Catalytic reforming technologies are among the most widely studied pathways for generating H₂. Conventional processes such as dry reforming, steam reforming, and partial oxidation of methane (CH₄) convert CH₄ into synthesis gas (H₂ and CO) or H₂ [5,6]. Moreover, emerging technologies focusing on renewable feedstocks, such as photocatalytic H₂ production and the use of H₂ carriers, have expanded the pathways for catalytic H₂ generation beyond the conventional fossil-based pathways [7,8].

The Special Issue, entitled “Catalytic Reforming and Hydrogen Production: From the Past to the Future, 2nd Edition”, aims to highlight recent advances in catalytic systems, reaction mechanisms, and process optimization strategies for producing H₂. The first Special Issue [9] focused on advances in methane/methanol reforming and photocatalytic H₂ production processes as well as important developments in catalytic materials for sustainable H₂ generation. Additional contributions are presented in this Special Issue that expand the scientific scope of the first Special Issue [9], covering catalytic reforming of hydrocarbons and renewable feedstocks, photocatalytic H₂ evolution, and H₂ generation from chemical carriers.

The contributions included in this Special Issue can be categorized into four main thematic groups, reflecting the diversity of the catalytic approaches currently being explored for producing H₂. These categories include (i) CH₄ reforming catalysts, (ii) reforming of renewable feedstocks, (iii) photocatalytic H₂ production, and (iv) H₂ generation from chemical carriers (Figure 1).

Methane reforming processes are the most studied catalytic routes for producing H₂ and syngas. Several contributions in this Special Issue focus on the development of advanced catalytic systems designed to increase their activity, stability, and resistance to carbon deposition.

Wang et al. (Contribution 1) prepared tourmaline-supported Ni-NiAl₂O₄ nanocomposite catalysts via a microwave hydrothermal reduction method for the dry reforming of the CH₄ (DRM) reaction. The results demonstrate that the tourmaline support effectively enhanced the dispersion of Ni species and improved catalytic performance, particularly under relatively low temperatures (500–600 °C). The increased catalytic activity highlights the potential of using natural mineral supports as cost-effective alternatives for stabilizing Ni-based catalysts.

Bong et al. (Contribution 2) studied the influence of surface basicity in mixed Ni/ZrO₂-based oxide catalysts for the oxythermal reforming of CH₄ with CO₂. The authors found that incorporating alkaline earth promoters (e.g., Ca and Ba) into a Ni/ZrO₂ catalyst increased catalytic activity and stability during long-term operation. The enhanced performance of Ni-Ba-Ca/ZrO₂ was attributed to its increased surface basicity compared with that of Ni/ZrO₂, which facilitated the gasification of carbon species and suppressed coke formation.

Methane reforming reactions are also closely related to electrochemical energy conversion technologies such as solid oxide fuel cells (SOFCs). Ioannidou et al. (Contribution 3) investigated internal DRM in SOFC systems using modified Ni/GDC fuel electrodes. Adding Fe and Au dopants significantly enhanced the electrocatalytic activity and operational stability of the electrodes. Long-term experiments revealed extended operational lifetime and reduced degradation rates, thus highlighting the beneficial effect of Fe-Au co-doping on SOFC fuel electrode performance.

Converting renewable feedstocks into H₂ represents an important pathway toward the development of sustainable energy systems. Two contributions in this Special Issue address catalytic processes involving biomass-derived and bio-based feedstocks.

Qiu et al. (Contribution 4) produced H₂ through a two-stage pyrolysis-steam reforming process using municipal solid waste (MSW) and biomass feedstocks. Self-derived char-based catalysts prepared via pyrolysis residues were employed to enhance the reforming reactions. The catalysts effectively cracked tar and produced H₂ at reforming temperatures between 850 and 900 °C. Notably, the catalytic activity of the MSW-derived char catalysts was higher due to their higher active metal species contents, highlighting the potential of waste-derived catalysts for waste valorization and H₂ generation.

Ali et al. (Contribution 5) examined high-pressure ethanol steam reforming (ESR) using commercial nickel-based catalysts. This study demonstrates that high-pressure operation can increase H₂ purification efficiency and reduce downstream processing requirements. Ethanol was completely converted under optimized conditions (30 bar and temperatures up to 850 °C), with H₂ yields reaching 5.2 mol H₂ per mol of ethanol. These results highlight the potential of high-pressure reforming technologies for increasing the efficiency and scalability of producing H₂ from renewable alcohols.

Photocatalytic H₂ production has emerged as an attractive approach for utilizing solar energy to generate clean fuels. In this Special Issue, Ahmad and Oh provide a comprehensive review (Contribution 6) focusing on photocatalytic H₂ evolution using two-dimensional MoS₂-based materials. The review summarizes recent advances in the synthesis and application of MoS₂ composites with semiconductor materials such as metal oxides, graphene, carbon nanotubes and metal–organic frameworks (MOFs). These hybrid materials enhance charge separation efficiency and provide additional active sites, leading to increased H₂ evolution under visible light irradiation.

Another promising approach for producing H₂ involves the use of chemical H₂ carriers that allow safe storage and on-demand H₂ release. Wang et al. (Contribution 7) developed Pd nanoparticles supported on nitrogen-doped porous carbon cages derived from zeolitic imidazolate frameworks (ZIFs) for producing H₂ via formic acid dehydrogenation. The synthesized Pd/PNCC nanocatalysts (PNCC denotes porous nitrogen-doped carbon cages) exhibited excellent catalytic performance, with a turnover frequency of 3174 h⁻¹ under mild reaction conditions. The enhanced catalytic activity was attributed to strong metal–support interactions that optimized the electronic properties of the Pd active sites and facilitated efficient H₂ evolution.

The contributions included in this Special Issue highlight the continuous progress in catalytic technologies for producing H₂ production through conventional and emerging pathways. Several challenges remain to be addressed for achieving the large-scale implementation of catalytic H₂ production technologies.

One of the main challenges facing H₂ production is developing highly stable catalysts that operate under harsh reaction conditions while maintaining high activity and resistance to deactivation phenomena such as carbon deposition, metal particle sintering, or catalyst poisoning. For example, coke formation and catalyst deactivation in CH₄ reforming processes require further investigation through improved catalyst design and the optimization of reaction conditions.

Another important research direction involves the efficient use of renewable feedstocks such as biomass, municipal waste, and bio-derived alcohols. The integration of catalytic reforming processes with waste valorization strategies can significantly contribute to circular economy approaches while reducing the environmental impacts of the process. Additionally, further advancements in photocatalytic H₂ production and H₂ carrier technologies could offer complementary solutions for sustainably generating and storing H₂.

Future research efforts should focus on the development of advanced catalytic materials with increased activity, stability, and cost-effectiveness, as well as elucidating the reaction mechanisms. The integration of catalytic H₂ production processes with renewable energy sources and emerging energy technologies will also play a crucial role in the transition toward a sustainable H₂ economy.

The studies presented in this Special Issue provide valuable insights into these challenges and demonstrate the broad range of catalytic strategies currently being explored to advance H₂ production technologies. Continued research in this field will be essential for developing efficient and sustainable catalytic systems capable of supporting the global transition toward clean energy solutions.