Cleaner Chemical Engineering is a platform to analyse and debate the role of chemical engineering in the period of energy transition and environmental protection. In this light, achieving CLEANER chemical engineering is a significant challenge as most of the energy today is still being extracted by chemical conversion of fossil fuels, releasing a vast amount of environmentally dangerous and harmful gases. Both Energy Transition and Environmental Protection require the utilization of new technologies and energy sources. There are opportunities and barriers to a clean energy and environment transition in the resource (land, water and air), power, transportation, and industry sectors. The most prominent approach to mid-term emission reduction is the improvement of existing fuel processing technologies, which also contribute to environmental protection addressing climate change. In the advancement of industry, transport and energy production sectors, there are still technical challenges to be solved, and most are related to physical and chemical phenomena accruing in the thermo-chemical reactors and chambers. At the same time, adopting renewable energies and novel remediation technologies would further secure a clean environment.