The Promethean Particles Family
Meet Our Team
PROMETHEAN PARTICLES’ LEADERSHIP TEAM
James
Stephenson
Chief Executive
Officer
James Stephenson
With an extensive background in chemical manufacturing and processing, James’ career spans both sides of the Atlantic. He worked for Dow Corning (now Dow) for more than 16 years in the UK and United States, where he became global product manager for its electronics and advanced materials business.
He also led an internal start-up for the development of silicon nanoparticle-based inks for printed electronics. Since then, he was the general manager/managing director for Polyone Corporation (now Avient) and the vice president, Global Business Development, at Carlisle Fluid Technologies.
In 2020, he joined Promethean Particles as CEO. He holds an M. Eng in chemical engineering from Swansea University, an MBA from Manchester Business School, and is a Fellow of the Chartered Institute of Marketing.
Paul
Denney
Chief Financial
Officer
Paul Denney
Paul joined Promethean Particles as Chief Financial Officer in September 2025. He established his career in financial management with the IT outsourcing business, Electronic Data Systems Inc. (now part of Hewlett Packard), working in the UK, Spain and Latin America. He subsequently broadened his international career in the data and analytics sector, managing in-house M&A teams at both Experian plc and at Callcredit Information Group. Most recently, Paul was CFO for 6 years at Xeros Technology Group plc, an AIM-listed greentech business and at an early-stage life sciences spin-out from Newcastle University.
Paul is a CIMA-qualified accountant and has an MBA from the London Business School.
Steve
Williams
Commercial
Director
Steve Williams
Steve is a seasoned global commercial leader with extensive international experience across the energy, industrial, and defence sectors. His career spans five continents and includes leadership roles in both Fortune 500 organisations and start-ups, where he has successfully expanded engineering & technology businesses into new markets, diversified service portfolios, and developed high-value strategic partnerships.
Prior to joining Promethean Particles in 2026, Steve held senior commercial and operational leadership roles with organisations including Schlumberger, Newpark, and Alfa Laval, working across the UK, Europe, Africa, Middle East, Asia-Pacific, and North America.
Selina
Ambrose
Product
Manager
Selina Ambrose
Selina has more than 14 years of experience in the development and commercialisation of advanced material technologies. After being promoted into her current role in 2022,
Selina now leads the product management function at Promethean, acting as the critical interface between external needs of customers and collaboration partners, and the internal capabilities to deliver them. Prior to this, Selina held the position of Promethean’s technical manager, where she played a key role in successfully winning over £3.5 million in non-dilutive, grant funding for the company to deliver a range of innovative R&D projects.
Selina holds a PhD in Chemical Engineering from the University of Nottingham, where her thesis focused on the continuous-flow hydrothermal synthesis of functional nanomaterials. She is currently an advisory board member of the University of Nottingham Sustainable Chemistry CDT.
Owen
Cartmell
Operations
Manager
Owen Cartmell
Owen joined Promethean Particles in 2023 to lead the engineering and production functions and accelerate the delivery of our products to our customers. Owen has more than 10 years experience in the chemical industry, previously working in the FMCG and Fine & Specialty Chemical sectors for Reckitt Benckiser and Thermo Fisher Scientific.
He holds an MSc in Chemical Engineering from the University of Leeds, and a BSc in Chemistry also from the University of Leeds. He is an Associate Member of the IChemE, working towards Chartership.
Leah
Matsinha
Research & Development
Manager
Leah Matsinha
Leah joined Promethean’s R&D team as a Senior Technical Scientist in 2024. She is an experienced MOF synthetic chemist who has led projects in both academia and industry, with applications including catalysis, CO2 activation, and CO2 capture & sequestration. Before Promethean, she worked as part of the R&D team at Concrete4Change, and also held research and academic positions at the University of South Wales and the University of Johannesburg, respectively.
Leah holds a PhD in Chemistry from University of Cape Town. She is also a fellow of the Royal Society’s Future Leaders: African Independent Researcher (FLAIR) programme.
Ed
Lester
Founder & Chief Scientific
Officer
Ed Lester
Ed is part of the Advanced Materials Research Group and the Lady Trent Professor of Chemical Engineering, Faculty of Engineering, at the University of Nottingham. He has a PhD in chemical engineering.
For more than 20 years, Ed has researched many topics, including power generation and fuel combustion. But one area of research — on continuous supercritical fluid reactors — led to the launch of Promethean Particles, where he is the chief scientific officer.
He also works on projects where his research interests overlap: chemicals and energy from biomass waste, through gasification, supercritical water oxidation, hydrothermal extraction or thermal upgrading.
Interested in joining Promethean Particles? Contact our Careers team to apply for a specific role or make a speculative enquiry.
