MOSS LANDING, Calif. — It seems like alchemy: a Silicon Valley start-up says it has found a way to capture the carbon dioxide emissions from coal and gas power plants and lock them into cement.

If it works on a mass scale, the company, Calera, could turn that carbon into gold.

Cement production is a large source of carbon emissions in the United States, and coal-fired electricity plants are the biggest source. As nations around the world press companies to curb their greenhouse-gas emissions, a technology that makes it profitable to do so could be very popular. Indeed, Calera’s marketing materials may be one of the rare places where glowing quotes from a coal company and the Sierra Club appear together.

“With this technology, coal can be cleaner than solar and wind, because they can only be carbon-neutral,” said Vinod Khosla, the Silicon Valley billionaire. His venture capital firm, Khosla Ventures, has invested about $50 million in Calera. On Monday, Calera is set to announce that Peabody Energy, the world’s biggest coal company, has invested $15 million.

Although Calera has a pilot project up and running, it is still not clear that the process can be used on a large scale or that anyone will buy the cement it makes.