# Analysis of the Sugarane Biomass Use to Produce Green Hydrogen: Brazilian Case Study
## 1 Introduction
This global distribution underscores the collaborative nature of biohydrogen research, with diverse nations contributing according to their unique resources and priorities. Together, these efforts support the ongoing global transition to clean and sustainable energy sources. The keyword co-occurrence network in Figure 3 illustrates the relationships among the most significant keywords and their frequencies, based on articles analyzed from Scopus and Clarivate Analytics WoS. The data from these two databases were merged using the R programming language. The network, created with VOSviewer software, version 1.6.20, includes 50 selected keywords grouped into six clusters, with a minimum co-occurrence threshold of four. Keyword variability is represented by font size, where larger fonts indicate higher frequencies. This approach provides a clear representation of the connections and relevance of terms related to biohydrogen production, supporting the identification of optimal keyword combinations for literature reviews. Figure 2: Top 10 countries: Article frequency and per capita proportion analysis. Data were sourced from the World Bank. Based on the visualization in Figure 3, the most prominent keyword is \"biohydrogen\", reflecting its central importance in the field of biohydrogen production. Other significant terms include \"lignocellulosic biomass\", \"pretreatment\", \"fermentation\", and \"biomass\", which highlight the focus on feedstock preparation, biological processes, and the conversion of organic materials for hydrogen production. Keywords such as \"anaerobic digestion\", \"biorefinery\", and \"enzymatic hydrolysis\" emphasize the role of advanced biological and chemical processes in this area of research. Furthermore, terms like \"sugarcane bagasse\", \"cellulose\", and \"lignin\" underscore the use of specific biomass feedstocks, and the challenges associated with breaking down complex materials. \"Renewable energy\" and \"biochar\" reflect the broader integration of biohydrogen within sustainable energy systems, while keywords such as \"dark fermentation\", \"gasification\", and \"ionic liquid\" point to various methodologies being explored to enhance production efficiency. In conclusion, these keywords demonstrate a clear emphasis on sustainable and biological methods for hydrogen production. The interconnectedness of terms reflects a multidisciplinary approach, integrating concepts from biochemistry, renewable energy, and waste-to-energy processes. This highlights the ongoing efforts to improve efficiency, optimize processes, and utilize diverse organic feedstocks, contributing to advancements in clean and sustainable energy solutions. The integration of biohydrogen with other renewable energy sectors, such as bioethanol and methane production, illustrates a holistic approach to advancing clean energy solutions. Table 1 further emphasizes this multidisciplinary approach by associating these main keywords with the corresponding relevant articles, reflecting a strong emphasis on sustainability and environmental responsibility in biohydrogen technologies. Figure 3: Keyword co-occurrence network, 2019–2023 (Scopus and Clarivate Analytics WoS). The studies reviewed point to a variety of pretreatment strategies, including acid, thermal, enzymatic, and hydrothermal treatments, that improve the conversion of lignocellulosic sugars into fermentable substrates. [PERSON] et al. (2020) focused on acidic and thermal pretreatments for enhancing the anaerobic digestion process and improving hydrogen and volatile fatty acid production from xylose, demonstrating the relevance of such approaches for lignocellulosic biomass, including sugarcane (16). Likewise, [PERSON] et al. (2021) reviewed the sequential production of hydrogen and methane through the