When BASF first made its hostile takeover bid in January, $37 (31 euros) per share or $4.9 billion (four billion euros), the Iselin, New Jersey, company rejected the offer as too low and told its board-advised shareholders not to tender their shares.

Engelhard still views the offer as inadequate, describing it in a statement as "not in the best interest of Engelhard shareholders."

But BASF announced Thursday it is extending the offer until April 14, after it signed a confidentiality agreement with the US company which allows it "to review non-public information." That agreement has left BASF upbeat that Engelhard was reconsidering the offer, according to the Financial Times.

If the deal goes through it would be BASF's biggest-ever buy. The German company wants to use some of its recent sky-high profits to buy into the fast-expanding catalyst sector, which is more resistant to the economic cycle as its core chemicals business.