Johnson Matthey, the world's largest maker of catalysts to control car emissions, posted a 13% rise in first-half profit, helped by increased global production of cars and trucks and demand for its specialty catalysts.

The British specialty chemicals firm - which also refines and recycles platinum group metals - said underlying profit before tax totaled £212.9 million ($344.3 million) for the six months to the end of September, in line with analyst expectations and up from a restated £187.9 million a year ago.

It forecast a second half performance broadly in line with the first six months of its financial year. That excludes the impact of the end of long-standing platinum buying and other arrangements with Anglo American Platinum in the new year, which ended a key discount.

The group's key Emission Control Technologies division, which manufactures auto catalysts, posted a 16% rise in underlying operating profit thanks to growth in sales across regions. That includes long-depressed Europe, where demand for catalysts for trucks and other heavy duty vehicles rose ahead of new legislation - Euro VI - coming into force in January.

Finance Director Robert MacLeod said the group had seen customers for smaller trucks buying up cheaper Euro V trucks ahead of the deadline, and buyers of larger vehicles coming in early for Euro VI trucks to benefit from fuel efficiency.

He said the impact of the "pre-buying" on sales in the second half of the group's financial year was unclear.

"We have had a pull forward of orders into this half, or this calendar year, ahead of the new legislation," MacLeod said.

"No one really knows what is going to happen (in 2014). The truck fleet in Europe is pretty old too - are some of these orders just getting the fleet back up to the right age?"

Process Technologies, the division which makes specialty catalysts, said sales climbed 15% and underlying operating profit rise 17%, helped by the acquisition of formaldehyde producer Formox in March.

It forecast a second-half performance for the unit "slightly ahead" of the first half.